8. On the Discovery of Electromagnetism, Chapter 4, Faraday, Barlow and others devised experimental apparatus for producing rotary motion from the electric current, and in 1831 Joseph Henry, the famous American electrician, invented a small electromagnetic engine or motor. These early machines were actuated by the current from a voltaic battery, but in the middle of the century Jacobi found that a dynamo-electric generator can also work as a motor, and that by coupling two dynamos in circuit, one as a generator, the other as a motor, it was possible to transmit mechanical power to any distance by means of electricity. Figure 76 is a diagram of a simple circuit for the transmission of power, where d is the technical symbol for a dynamo as a generator, having its poles plus and minus connected by wire to the poles of m, the distant dynamo, as a motor. The generator d is driven by mechanical energy from any convenient source, and transforms it into electric energy, which flows through the circuit in the direction of the arrows, and in traversing the motor m, is re-transformed into mechanical energy. There is, of course, a certain waste of energy in the process, but with good machines and conductors it is not more than 10 to 25 percent, or the efficiency of the installation is from 75 to 90 percent. That is to say, for every 100 horsepower put into the generator, from 75 to 90 horsepower are given out again by the motor. It was not until 1870, when Graham had improved the dynamo, that power was practically transmitted in this way, and applied to pumping water and other work. Since then great progress has been made, and electricity is now recognized not only as a rival of steam, but as the best means of distributing steam, wind, water or any other power to a distance, and bringing it to bear on the proper point. The first electric railway, or rather tramway, was built by Dr. Werner von Siemens at Berlin in 1879, and was soon followed by many others. The wheels of the car were driven by an electric motor, drawing its electricity from the rails, which were insulated from the ground, and being connected to the generator served as conductors. It was found very difficult to insulate the rails and keep the electricity from leaking to the ground, however, and at the Paris Electrical Exhibition of 1881, von Siemens made a short tramway in which the current was drawn from a bare copper conductor, running on poles like a telegraph wire along the line. The system will be understood from figure 77, where L is the overhead conductor joined to the positive pole of the dynamo or generator in the powerhouse, and C is a rolling contact or trolleywheel travelling with the car, and connected by the wire W to an electric motor M under the car, and geared to the axles. After passing through the motor, the current escapes to the rail R by a brush or sliding contact C1, and so returns to the negative pole of the generator. A very general way is to allow the return current to escape to the rails through the wheels. Many tramways covering thousands of miles are now worked on this plan in the United States. At Bangor, Maine, a modification of it is in use whereby the conductor is divided into sections, alternately connected to the positive and negative poles of two generators, coupled together as in the three-wire system of electric lighting, Page 119, their middle poles being joined to the earth, that is to say the rails. It enables two cars to be run on the same line at once, and with a considerable saving of copper. To make the car independent of the conductor L for a short time, as in switching, a battery of accumulators B may be added and charged from the conductor, so that when the motor is disconnected from the conductor, the discharge from the accumulator may still work it and drive the wheels. Attempts have been made to run tram cars with the electricity supplied by accumulators alone, but the system is not economical owing to the dead weight of the cells and the periodical trouble of recharging them at the generating station. On heavy railroads worked by electricity, the overhead conductor is replaced by a third rail along the middle of the track, and insulated from the ground. In another system the middle conductor is buried underground, and the current is tapped at intervals by the motor connecting with it for a moment by means of spring contacts as the car travels. In each case however the outer rails serve as the return conductors. Another system puts one or both the conductors in a conduit underground, the trolley pole entering through a narrow slot similar to that used on cable roads. The first electric carriages for ordinary roads were constructed in 1889 by Mr. Magnus Vogue of Brighton. Figure 78 represents one of these made for the Sultan of Turkey, and propelled by a one-horsepower, image electric motor, geared to one of the hind wheels by means of a chain. The current for the motor was supplied by 30 EPS accumulators stowed in the body of the vehicle, and of sufficient power to give a speed of ten miles an hour. The driver steers with a hand lever, as shown, and controls the speed by a switch in front of him. Vans, bath-chairs and tricycles are also driven by electric motors, but the weight of the battery is a drawback to their use. In or about the year 1839, Jacobi sailed an electric boat on the Neva, with the help of an electromagnetic engine of one horsepower, fed by the current from a battery of growth cells, and in 1882 a screw launch carrying several passengers and propelled by an electric motor of three horsepower, worked by 45 accumulators, was tried on the Thames. Being silent and smokeless in its action, the electric boat soon came into favour, and there is now quite a flotilla on the river, with power stations for charging the accumulators at various points along the banks. Figure 79 illustrates the interior of a handsome electric launch, the Lady Cooper, built for the EPS, or Electric Power Storage Company. An electric motor in the after-part of the hull is coupled directly to the shaft of the screw propeller, and fed by EPS accumulators in teak boxes lodged under the deck amid ships. The screw is controlled by a switch and the rudder by an ordinary helm. The cabin is seven feet long and lighted by electric lamps. Some signals are given by an electric gong, and a search light can be brought into operation whenever it is desirable. The speed attained by the Lady Cooper is from 10 to 15 knots.  It can travel entirely underwater, below the agitation of the waves, where sea-sickness is impossible, and the inventor hopes that vessels of the kind will yet carry passengers across the channel. The screw propeller of the Edison and Sims torpedo is also driven by an electric motor. In this case, the current is conveyed from the ship or fort which discharges the torpedo by an insulated conductor running off a reel carried by the torpedo, the earth or return half of the circuit being the sea-water. All sorts of machinery are now worked by the electric motor, for instance cranes, elevators, capstones, riveters, lathes, pumps, chaff-cutters and sores. Of domestic appliances, Figure 80 shows an air propeller or ventilation fan, where F is a screw-like fan attached to the spindle of the motor M and revolving with its armature. Figure 81 represents a Truvet motor working a sewing machine, where N is the motor which gears with P the driving axle of the machine. Figure 82 represents a fine drill actuated by a Griscum motor. The motor M is suspended from a bracket ABC by the tackle DE, and transmits the rotation of its armature by a flexible shaft ST to the terminal drill O, which can be applied at any point and is useful in boring teeth. Now that electricity is manufactured and distributed in towns and villages for the electric light, it is more and more employed for driving the lighter machinery. Steam, however, is more economical on a large scale, and still continues to be used in great factories for the heavier machinery. Nevertheless, a day is coming when coal, instead of being carried by rail to distant works and cities, will be burned at the pit mouth, and its heat transformed by means of engines and dynamos into electricity for distribution to the surrounding country. I have shown elsewhere that peat can be utilised in a similar manner, and how the great Borg of Allen is virtually a neglected goldfield in the heart of Ireland. The sunshine of deserts, and perhaps the electricity of the atmosphere, but at all events the power of winds, waves and waterfalls are also destined to whirl the dynamo and yield as light, heat or motion. Much has already been done in this direction. In 1891 the power of turbines driven by the falls of Necker at Loughan was transformed into electricity, and transmitted by a small wire to the electrical exhibition of Frankfurt on the mine a hundred and seventeen miles away. The city of Rome is now lighted from the falls of Tivoli, sixteen miles distant. The finest cataract in Great Britain, the falls of Foyers in the Highlands, which persons of taste and culture wish to preserve for the nation, is being sacrificed to the spirit of trade, and deprived of its waters for the purpose of generating electricity to reduce aluminium from its oars. The great scheme recently completed for utilising the power of Niagara Falls by means of electricity is a triumph of human enterprise which outrivals some of the bold creations of Jules Verne. When in 1678 the French missionaries La Salle and Enepin discovered the stupendous cataract on the Niagara River between Lake Ontario and Lake Erie, the science of electricity was in its early infancy, and little more was known about the mysterious force, which is performing miracles in our day, than its manifestation on rubbed amber, ceiling wax, glass and other bodies. Nearly a hundred years had still to pass ere Franklin should demonstrate the identity of the electric fire with lightning, and nearly another hundred before Faraday should reveal a mode of generating it from mechanical power. Assuredly neither La Salle nor his contemporaries ever dreamed of a time when the water power of the falls would be distributed by means of electricity to produce light or heat and serve all manner of industries in the surrounding district. The awestruck Iroquois Indians had named the cataract Onyagara, or Thunder of the Waters, and believed it the dwelling-place of the spirit of thunder. This poetical name is nonetheless appropriate, now that the modern electrician is preparing to draw his lightnings from its waters and compel the genius loci to become his willing bondsman. The falls of Niagara are situated about twenty-one miles from Lake Erie, and fourteen miles from Lake Ontario. At this point the Niagara River, nearly a mile broad, flowing between level banks and parted by several islands, is suddenly shot over a precipice a hundred and seventy feet high, and making a sharp bend to the north pursues its course through a narrow gorge towards Lake Ontario. The falls are divided at the brink by Goat Island, whose primeval woods are still thriving in their spray. The horseshoe fall on the Canadian side is eight hundred and twelve yards, and the American falls on the south side are three hundred and twenty-five yards wide. For a considerable distance both above and below the falls, the river is turbulent with rapids. The water power of the cataract has been employed from olden times. The French fur traders placed a mill beside the upper rapids, and the early British settlers built another to saw the timber used in their stockades. By and by the Steadman and Porter mills were established below the falls, and subsequently others, which derived their water supply from the lower rapids by means of raceways or leads. Eventually an open hydraulic canal, three-fourths of a mile long, was cut across the elbow of land on the American side, through the town of Niagara Falls, between the rapids above and the verge of the chasm below the falls, where since 1874 a cluster of factories has arisen, which discharged their spent water over the cliff in a series of cascades almost rivalling Niagara itself. This canal, which only taps a mere drop from the ocean of power that is running to waste, has been utilised to the full, and the decrease of water privileges in the New England states owing to the clearing of the forests and settlement of the country, together with the growth of the electrical industries, have led to a further demand on the resources of Niagara. With the example of Minneapolis, which draws the power for its many mills from the falls of St. Anthony in the Mississippi River before them, a group of far-seeing and enterprising citizens of Niagara Falls resolved to satisfy this requirement by the foundation of an industrial city in the neighbourhood of the Falls. They perceived that a better site could nowhere be found on the American continent. Apart from its healthy air and attractive scenery, Niagara is a kind of halfway house between the East and West, the consuming and the producing states. By the Erie Canal at Turner Wanda, it commands the great waterway of the lakes in the St. Lawrence. A system of trunk railways from different parts of the states and Canada are focused there, and cross the river by the cantilever and suspension bridges below the falls. The New York Central and Hudson River, the Lehigh Valley, the Buffalo, Rochester and Pittsburgh, the Michigan Central and the Grand Trunk of Canada are some of these lines. Jaining as it does the great lakes of the interior, which have a total area of 92,000 square miles, with an aggregate basin of 290,000 square miles, the volume of water in the Niagara River passing over the cataract every second is something like 300,000 cubic feet, and this, with a fall of 276 feet from the head of the upper rapids to the whirlpool rapids below, is equivalent to about nine million, or allowing for waste in the turbines, say seven million horsepower. Moreover the great lakes discharging into each other form a chain of immense reservoirs, and the level of the river being little affected by flood or drought, the supply of pure water is practically constant all the year round. Mr. R. C. Reed has shown that a rainfall of three inches in twenty-four hours over the basin of Lake Superior would take ninety days to run off into Lake Huron, which with Lake Michigan would take as long to overflow into Lake Erie, and therefore six months would elapse before the full effect of the flood was expended at the falls. The first outcome of the movement was the Niagara River Hydraulic Power and Sewer Company, incorporated in 1886, and succeeded by the Niagara Falls Power Company. The old plan of utilizing the water by means of an open canal was unsuited to the circumstances, and the company adopted that of the lake Mr. Thomas Evershed, divisional engineer of the New York State canals. Like the other it consists in tapping the river above the falls, and using the pressure of the water to drive the number of turbines, then restoring the water to the river below the falls. But instead of a surface canal the tail-race is a hydraulic tunnel or underground conduit. To this end some fifteen hundred acres of spare land, having a frontage just above the upper rapids, was quietly secured at the low price of three hundred dollars an acre. And we believe its rise in value owing to the progress of the works is such that a yearly rental of two hundred dollars an acre can even now be got for it. This land has been laid out as an industrial city, with a residential quarter for the operatives, wharves along the river, and sidings or short lines to connect with the trunk railways. In carrying out their purpose the company has budded and branched into other companies, one for the purchase of the land, another for making the railways, and a third, the Cataract Construction Company, which is charged with the carrying out of the engineering works for the utilization of the water power, and is therefore the most important of all. A subsidiary company has also been formed to transmit by electricity a portion of the available power to the city of Buffalo at the head of the Niagara River on Lake Erie, from twenty miles distant. All these affiliated bodies are, however, under the directorate of the Cataract Construction Company, and amongst those who have taken the most active part in the work, we may mention the President, Mr. E. D. Adams, Professor Coleman Sellers, the Consulting Engineer, and Professor George Forbes, FRS, the Consulting Electrical Engineer, a son of the late Principal Forbes of Edinburgh. In securing the necessary right of way for the hydraulic tunnel, or in the acquisition of land, the company has shown consummate tact. A few proprietors declined to accept its terms, and the company selected a parallel route. Having obtained the right of way for the latter, it informed the refractory owners on the first line of their success, and intimated that the company could now dispense with that. On this the sticklers professed their willingness to accept the original terms, and the bargain was concluded, thus leaving the company in possession of the rights of way for two tunnels, both of which they propose to utilise. The liberal policy of the directors is deserving of the highest commendation. They have risen above mere chauvinism, and instead of narrowly confining the work to American engineers, they have availed themselves of the best scientific counsel which the entire world could afford. The great question as to the best means of distributing and applying the power of their command had to be settled, and in 1890, after Mr. Adams and Dr. Sellers had made a visit of inspection to Europe, an international commission was appointed to consider the various methods submitted to them, and award prizes to the successful competitors. Lord Kelvin, then Sir William Thomson, was the President, and Professor W. C. Unwin, the well-known expert in hydraulic engineering, the Secretary, while other members were Professor Mascar of the Institute, a leading French electrician, Colonel Turretini of Geneva, and Dr. Sellers. A large number of schemes were sent in, and many distinguished engineers gave evidence before the commission. The relative merits of compressed air and electricity, as a means of distributing the power, were discussed, and on the whole the balance of opinion was in favour of electricity. Prizes of two hundred and two hundred and fifty pounds were awarded to a number of firms who had submitted plans, but none of these were taken up by the company. The impulse turbines of Messers Fesh and Picard of Geneva, who gained a prize of two hundred and fifty pounds, have, however, been adopted since. It is another proof of the determination of the company to procure the best information on the subject, regardless of cost, that Professor Forbes had carte blanche to go to any part of the world and make a report on any system of electrical distribution which he might think fit. With the selection of electricity another question arose as to the expediency of employing continuous or alternating currents. At that time continuous currents were chiefly in vogue, and it speaks well for the sagacity and prescience of Professor Forbes that he boldly advocated the adoption of alternating currents, more especially for the transmission of power to Buffalo. His proposals encountered strong opposition, even in the highest quarters, but since then partly owing to the striking success of the Lauff and to Frankfurt experiment in transmitting power by alternating currents over a bare wire on poles a distance of more than a hundred miles, the directors and engineers have come round to his view of the matter, and alternating currents have been employed at all events for the Buffalo Line, and also for the chief supply of the industrial city. Continuous currents flowing always in the same direction, like the current of a battery, can, it is true, be stored in accumulators, but they cannot be converted to higher or lower pressure in a transformer. Alternating currents on the other hand, which seesaw in direction many times a second, cannot be stored in accumulators, but they can be sent at high pressure along a very fine wire, and then converted to higher or lower pressures where they are wanted, and even to continuous currents. Each kind therefore has its peculiar advantages, and both will be employed to some extent. With regard to the engineering works, the hydraulic tunnel starts from the bank of the river where it is navigable, at a point a mile and a half above the falls, and after keeping by the shore it cuts across the bend beneath the city of Niagara Falls, and terminates below the suspension bridge under the falls at the level of the water. It is 6,700 yards long, and of a horseshoe section, 19 feet wide, by 21 feet high. It has been cut 160 feet below the surface through the limestone and shale, but is arched with brick, having rubble above, and at the outfall is lined on the invert or underside with iron. The gradient is 36 feet in the mile, and the total fall is 205 feet, of which 140 feet are available for use. The capacity of the tunnel is 100,000 horsepower. In the lands of the company it is 400 feet from the margin of the river to which it is connected by a canal, which is over 1,500 feet long, 500 feet wide at the mouth, and 12 feet deep. Out of this canal, headraces fitted with sluices conduct the water to a number of wheel pits, 160 feet deep, which have been dug near the edge of the canal, and communicate below with the tunnel. At the bottom of each wheel pit a 5,000 horsepower Girard double turbine is mounted on a vertical shaft, which drives a propeller shaft rising to the surface of the ground. A dynamo of 5,000 horsepower is fixed on the top of this shaft, and so driven by it. The upward pressure of the water is ingeniously contrived to relieve the foundation of the weight of the turbine shaft and dynamo. Twenty of these turbines, which are made by the IP Morris Company of Philadelphia from the designs of Messers Fesh and Picard, will be required to utilise the full capacity of the tunnel. The company possesses a strip of land extending two miles along the shore, and in excavating the tunnel a coffer dam was made with the extracted rock to keep the river from flooding the works. This dam now forms part of a system by which a tract of land has been reclaimed from the river. Part of it has already been acquired by the Niagara Paper Pulp Company, which is building gigantic factories and will employ the tail-race or tunnel of the cataract construction company. Warfs for the use of ships and canal boats will also be constructed on this frontage. By land and water the raw materials of the West will be conveyed to the industrial town, which is now coming into existence. Grain from the prairies of Illinois and Dakota, timber from the forests of Michigan and Wisconsin, coal and copper from the mines of Lake Superior, and whatnot. It is expected that one industry having a seat there will attract others. Thus the pulp mills will bring the makers of paper wheels and barrels. The smelting of iron will draw foundries and engine works. The electrical refining of copper will lead to the establishment of wireworks, cable factories, dynamo shops, and so on. Aluminium too promises to create an important industry in the future. In the meantime the cataract construction company is about to start an electrical factory of its own, which will give employment to a large number of men. It has also undertaken the water supply of the adjacent city of Niagara Falls. The cataract electric company of Buffalo has obtained the exclusive right to use the electricity transmitted to that city, and the line will be running a subway. This underground line will be more expensive to make than an overhead line, but it will not require to be renewed every eight to fifteen years, and it will not be liable to interruption from the heavy gales that sweep across the lakes, or the weight of frozen sleet. Moreover it will be more easily inspected and quite safe for the public. We should also add that in addition to the contemplated duplicate tunnel of a hundred thousand horsepower, the cataract construction company owns a concession for utilizing two hundred and fifty thousand horsepower from the horseshoe falls on the Canadian side in the same manner. It has thus a virtual monopoly of the available water power of Niagara, and the promoters have not the least doubt that the enterprise will be a great financial success. Already the Pittsburgh Reduction Company have begun to use the electricity in reducing aluminium from the mineral known as bauxite, an oxide of the metal, by means of the electric furnace. Another portion of the power is to be used to produce carbide of calcium for the manufacture of acetylene gas. At a recent electrical exhibition held in New York City a model of the Niagara plant was operated by an electric current brought from Niagara, four hundred and fifty miles distant, and a collection of telephones were so connected that the spectator could hear the roar of the real cataract. Thanks to the foresight of New York State and Canada the scenery of the falls has been preserved by the institution of public parks, and the works in question will do nothing to spoil it, especially as they will be free from smoke. Mr. Bogart's state engineer of New York estimates that the water drawn from the river will only lower the mean depths of the falls about two inches, and will therefore make no appreciable difference in the view. All together the enterprise is something new in the history of the world. It is not only the grandest application of electrical power, but one of the most remarkable feats, in an age when romance has become science, and science has become romance. End of Chapter 8 Chapter 9 of The Story of Electricity This LibriVox recording is in the public domain, recording by Ruth Golding. The Story of Electricity by John Monroe. Chapter 9 Minor Uses of Electricity The electric, trembling bell now in common use was first invented by John Mirand in 1850. Figure 83 shows the scheme of the circuit, where B is a small battery, say two or three dry or laclange cells joined by insulated wire to P, a pressed button or contact key, and G, an electromagnetic gong or bell. On pressing the button P, a spring contact is made, and the current flowing through the circuit strikes the bell. The action of the contact key will be understood from Figure 84, where P is the pressed button removed to show the underlying mechanism, which is merely a metal spring, A, over a metal plate, B. The spring is connected by wire to a pole of the battery, and the plate to a terminal or binding screw of the bell, or vice versa. When the button P is pressed by the finger, the spring is forced against the plate, the circuit is made, and the bell rings. On releasing the button it springs back, the circuit is broken, and the bell stops. Figure 85 shows the inner mechanism of the bell, which consists of a double-polled electromagnet M having a soft iron armature A hinged on a straight spring or tongue S, with one end fixed and the other resting against a screw contact T. The hammer H projects from the armature beside the edge of the gong E. In passing through the instrument the current proceeds from one terminal, say that on the right, by the wire W to the screw contact T, dense by the spring S through the bobbins of the electromagnet to the other terminal. The electromagnet attracts the armature A, and the hammer H strikes the gong. But in the act the spring S is drawn from the contact T, and the circuit is broken. Consequently the electromagnet, no longer excited, lets the armature go, and the spring leaps back against the contact T, withdrawing the hammer from the gong. But the instrument is now as it was at first, the current again flows, and the hammer strikes the gong only to fly back a second time. In this way as long as the button is pressed by the operator the hammer will continue to tap the bell ringing sound. Press buttons are of various patterns, and either affixed to the wall or inserted in the handle of an ordinary bell-pull, as shown in figure 86. The ordinary electric bell actuated by a battery is liable to get out of order owing to the battery spending its force, or to the contacts becoming dirty. Magneto-electric bells have therefore been introduced of late years. With these no battery or interrupting contacts are required, since the bell-pull or press-button is made in the form of a small dynamo, which generates the current when it is pulled or pushed. Figure 87 illustrates a form of this apparatus where M P is the bell-pull and B the bell, these being connected by a double wire W to convey the current. The bell-pull consists of a horseshoe magnet M having a bobbin of insulated wire between its poles and mounted on a spindle. When the key P is turned round by the hand the bobbin moves in the magnetic field between the poles of the magnet, and the current thus generated circulates in the wires W, and passing through an electromagnet under the bell attracts its armature and strikes the hammer on the bell. Of course the bell may be placed at any distance from the generator. In other types the current is generated and the bell rung by the act of pulling, as in a common house bell. Electric bells in large houses and hotels are usually fitted up with indicators, as shown in Figure 88, which tell the room from which the call proceeds. They are serviceable as instantaneous signals, annunciators and alarms in many different ways. An outbreak of fire can be announced by causing the undue rise of temperature to melt a piece of tallow or fusible metal, and thus release a weight which tails on a press-button and closes the circuit of an electric bell. Or the rising temperature may expand the mercury in a tube like that of a thermometer until it connects two platinum wires fused through the glass and in circuit with a bell. Some employ a curving bimetallic spring to make the necessary contact. The spring is made by soldering strips of brass and iron back to back, and as these metals expand unequally when heated the spring is deformed and touches the contact which is connected in the circuit, thus permitting the current to ring the bell. A still better device, however, is a small box containing a thin metallic diaphragm, which expands with the heat, and sagging in the centre touches a contact screw, thus completing the circuit and allowing the current to pass. These automatic or self-acting fire alarms can, of course, be connected in the circuit of the ordinary street fire alarms, which are usually worked by pulling a handle to make the necessary contact. From what has been said, it will be easy to understand how the stealthy entrance of burglars into a house can be announced by an electric bell or warning lamp. If press buttons or contact keys are placed on the sashes of the windows, the posts of the door, or the treads of the stair, so that when the window or door is opened, or the tread bends under the footstep, an electric circuit is closed, the alarm will be given. Of course the connections need only be arranged when the device is wanted. Shops and offices can be guarded by making the current show a red light from a lamp hung in front of the premises, so that the night watchman can see it on his beat. This can readily be done by adjusting an electromagnet to drop a screen of red glass before the flame of the lamp. Saves and showcases forcibly opened can be made to signal the fact, and recently in the United States a thief was photographed by a flashlight kindled in this way, and afterwards captured through the likeness. The level of water in systems and reservoirs can be told in a similar manner by causing a float to rise with the water and make the required contact. The degree of frost in a conservatory can also be announced by means of the mercury thermostat already described, or some equivalent device. There are indeed many actual or possible applications of a similar kind. The Massey log is an instrument for telling the speed of a ship by the revolutions of a fly as it is towed through the water, and by making the fly complete a circuit as it revolves the number of turns a second can be struck by a bell on board. In one form of the electric log the current is generated by the chemical action of sink and copper plates attached to the log and immersed in the sea water, and in others provided by a battery on the ship. Captain Mivoy has invented an alarm for torpedoes and torpedo boats, which is a veritable watchdog of the sea. It consists of an iron bell jar inverted in the water and moored at a depth below the agitation of the waves. In the upper part of the jar, where the pressure of the air keeps back the water, there is a delicate needle contact in circuit with a battery and an electric bell or lamp, as the case may be, on the shore. Waves of sound passing through the water from the screw propeller of the torpedo, or indeed any ship, make and break the sensitive contact and ring the bell or light the lamp. The apparatus is intended to alarm a fleet lying at anchor or a port in time of war. Electricity has also been employed to register the movements of weathercocks and animometers. A few years ago it was applied successfully to telegraph the course marked by a steering compass to the navigating officer on the bridge. This was done without impeding the motion of the compass card by causing an electric spark to jump from a light pointer on the card to a series of metal plates round the bowl of the compass and actuate an electric alarm. The domestic telegraph, an American device, is a little dial apparatus by which a citizen can signal for a policeman, doctor, messenger, or carriage, as well as a fire engine, by the simple act of setting a hand on the dial. Alexander Bain was the first to drive a clock with electricity instead of weights, by employing a pendulum having an iron bob which was attracted to one side and the other by an electromagnet. But as its rate depends on the constancy of the current, which is not easy to maintain, the invention has not come into general use. The butterfly clock of Lemoine, which we illustrate in Figure 89, is an improved type, in which the bob of soft iron P swings to and fro over the poles of a double electromagnet M in circuit with a battery and contact key. When the rate is too slow, the key is closed, and a current passing through the electromagnet pulls on the pendulum, thus correcting the clock. This is done by the ingenious device of hip, shown in Figure 90, where M is the electromagnet P, the iron bob, from which projects a wire bearing a light vane B of mica in the shape of a butterfly. As the bob swings, the wire drags over the hump of the metal spring S, and when the bob is going too slowly, the wire thrusts the spring into contact with another spring T below, thus closing the circuit, and sending a current through the magnet M, which attracts the bob and gives a fillip to the pendulum. Local clocks controlled from a standard clock by electricity have been more successful in practice, and are employed in several towns, for example Glasgow. Behind local dials are electromagnets which, by means of an armature, working a frame and ratchet wheel, move the hands forward every minute or half minute as the current is sent from the standard clock. The electrical chronograph is an instrument for measuring minute intervals of time by means of a stylus tracing a line on a band of travelling paper or a revolving barrel of smoked glass. The current, by exciting an electromagnet, jerks the stylus, and the interval between two jerks is found from the lengths of the trace between them and the speed of the paper or smoked surface. Retarded clocks are sometimes employed as electric meters for registering the consumption of electricity. In these the current to be measured flows through a coil beneath the bob of the pendulum, which is a magnet and thus affects the rate. In other meters the current passes through a species of galvanometer, called an ampere meter, and controls the clockwork counter. In a third kind of meter the chemical effect of the current is brought into play, that of Edison, for example, decomposing sulphate of copper or more commonly of zinc. The electric light is now used for signalling and advertising by night in a variety of ways. Incandescent lamps inside a translucent balloon and their light controlled by a current key, as in a telegraph circuit so as to give long and short flashes according to the Morse code, are employed in the army. Signals at sea are also made by a set of red and white glow lamps, which are combined according to the code in use. The powerful arc lamp is extremely useful as a search light, especially on men of war and fortifications, and it has also been tried in signalling by projecting the beam on the clouds by way of a screen and eclipsing it according to a given code. In 1879 Professor Graham Bell, the inventor of the speaking telephone, and Mr. Summer Tamta, brought out an ingenious apparatus called the photophone, by which music and speech were sent along a beam of light for several hundred yards. The action of the photophone is based on the peculiar fact observed in 1873 by Mr. J. E. Mayhew, that the electrical resistance of crystalline selenium diminishes when a ray of light falls upon it. Figure 91 shows how Bell and Tamta utilised this property in the telephone. A beam of sun or electric light, concentrated by a lens, L, is reflected by a thin mirror, M, and after traversing another lens, L, travels to the parabolic reflector, R, in the focus of which there is a selenium resistance in circuit with a battery S and two telephones, T, T1. Now, when a person speaks into the tube at the back of the mirror M, the light is caused to vibrate with the sounds, and a wavering beam falls on the selenium, changing its resistance to the current. The strengths of the current is thus varied with the sonorous waves, and the words spoken by the transmitter are heard in the telephones by the receiver. The photophone is, however, more of a scientific toy than a practical instrument. Becquerel, the French chemist, found that two plates of silver, freshly coated with silver from a solution of chloride of silver and plunged into water, form a voltaic cell which is sensitive to light. This can be seen by connecting the plates through a galvanometer, and allowing a ray of light to fall upon them. Other combinations of the kind have been discovered, and Professor Minchin, the Irish physicist, has used one of these cells to measure the intensity of starlight. The induction balance of Professor Hughes is founded on the well-known fact that a current passing in one wire can induce a sympathetic current in a neighbouring wire. The arrangement will be understood from Figure 92, where P and P1 are two similar coils or bobbins of thick wire in circuit with a battery B and a microphone M, while S and S1 are two similar coils or bobbins of fine wire in circuit with a telephone T. It need hardly be said that when the microphone M is disturbed by a sound, the current in the primary coils P, P1, will induce a corresponding current in the secondary coils S, S1. But the coils S, S1 are so wound that the induction of P on S neutralises the induction of P1 on S1, and no current passes in the secondary circuit, hence no sound is heard in the telephone. When, however, this balance of induction is upset by bringing a piece of metal, say a coin, near one or other of the coils S, S1, a sound will be heard in the telephone. The induction balance has been used as a sonometer for measuring the sense of hearing, and also for telling base coins. The writer devised a form of it for divining the presence of gold and metallic ores which has been applied by Captain Mervoy in his submarine detector, for exploring the sea-bottom for lost anchors and sunken treasure. When President Garfield was shot, the position of the bullet was ascertained by a similar arrangement. The microphone is a means of magnifying feeble sounds has been employed for localising the leaks in water pipes and in medical examinations. Some years ago it saved a Russian lady from premature burial by rendering the faint beating of her heart audible. Edison's electric pen is useful in copying letters. It works by puncturing a row of minute holes along the lines of the writing, and thus producing a stencil plate, which, when placed over a clean sheet of paper and brushed with ink, gives a duplicate of the writing by the ink penetrating the holes to the paper below. It is illustrated in Figure 93, where P is the pen consisting of a hollow stem in which a fine needle, actuated by the armature of a small electromagnet, plies rapidly up and down and pierces the paper. The current is derived from a small battery B, and an inking roller like that used in printing serves to apply the ink. In 1878 Mr. Edison announced his invention of a machine for the storage and reproduction of speech, and the announcement was received with a good deal of incredulity, notwithstanding the partial success of Faber and others in devising mechanical articulators. The simplicity of Edison's invention, when it was seen and heard, elicited much admiration, and although his first instrument was obviously imperfect, it was nevertheless regarded as the germ of something better. If the words spoken into the instrument were heard in the first place, the likeness of the reproduction was found to be unmistakable. Indeed, so faithful was the replica that a member of the Academy of Sciences, Paris, stoutly maintained that it was due to ventriloquism or some other trickery. It was evident, however, that before the phonograph could become a practical instrument, further improvements in the nicety of its articulation were required. The introduction of the electric light diverted Mr. Edison from the task of improving it, although he does not seem to have lost faith in his pet invention. During the next ten years he accumulated a large fortune, and was the principal means of introducing both electric light and power to the world at large. This done, however, he returned to his earlier love, and has at length succeeded in perfecting it, so as to redeem his past promises and fulfil his hopes regarding it. The old instrument consisted, as is well known, of a vibrating tympan or drum, from the centre of which projected a steel point or stylus, in such a manner that on speaking to the tympan its vibrations would urge the stylus to dig into a sheet of tinfoil moving past its point. The foil was supported on a grooved barrel, so that the hollow of the groove behind it permitted the foil to give under the point of the stylus, and take a corrugated or wavy surface corresponding to the vibrations of the speech. Thus recorded on a yielding but somewhat stiff material, these undulations could be preserved, and at a future time made to deflect the point of a similar stylus, and set a corresponding diaphragm or tympan into vibration, so as to give out the original sounds, or an imitation of them. Tinfoil, however, is not a very satisfactory material on which to receive the vibrations in the first place. It does not precisely respond to the movements of the marking stylus in taking the impression, and does not guide the receiving stylus sufficiently well in reproducing sounds. Mr. Edison has therefore adopted wax in preference to it, and instead of tinfoil spread on a grooved support, he now employs a cylinder of wax to take the print of the vibrations. Moreover, he no longer uses the same kind of diaphragm to print and receive the sounds, but employs a more delicate one for receiving them. The marking cylinder is now kept in motion by an electric motor, instead of by hand turning, as in the earlier instrument. The new phonograph which we illustrate in figure ninety-four is about the size of an ordinary sewing machine, and is of exquisite workmanship, the performance depending to a great extent on the perfection and fitness of the mechanism. It consists of a horizontal spindle S, carrying at one end the wax cylinder C on which the sonorous vibrations are to be imprinted. Over the cylinder is supported a diaphragm, or tympan, T, provided with a conical mouthpiece M for speaking into. Under the tympan there is a delicate needle or stylus, with its point projecting from the centre of the tympan downwards towards the surface of the wax cylinder, so that when a person speaks into the mouthpiece the voice vibrates the tympan and drives the point of the stylus down into the wax, making an imprint more or less deep in accordance with the vibrations of the voice. The cylinder is kept revolving in a spiral path at a uniform speed, by means of an electric motor E, fitted with a sensitive regulator and situated at the base of the machine. The result is that a delicate and rigid trace is cut in the surface of wax along a spiral line. This is the sound record, and by substituting a finer tympan for the one used in producing it the ridges and inequalities of the trace can be made to agitate a light stylus resting on them, and cause it to set the delicate tympan into vibrations corresponding very accurately to those of the original sounds. The tympan employed for receiving is made of gold beater's skin, having a stud at its centre and a springy stylus of steel wire. The sounds emitted by this device are almost a whisper, as compared to the original ones, but they are faithful in articulation, which is the main object, and they are conveyed to the ear by means of flexible hearing tubes. These tympans are interchangeable at will, and the arm which carries them is also provided with a turning tool for smoothing the wax cylinder prior to its receiving the print. The cylinders are made of different sizes, from one to eight inches long and four inches in diameter. The former has a storage capacity of two hundred words. The next in size has twice that, or four hundred words, and so on. Mr. Edison states that four of the large eight-inch cylinders can record all nickel-less nickel bit, which could therefore be automatically read to a private invalid or to a number of patients in a hospital simultaneously, by means of a bunch of hearing tubes. The cylinders can be readily posted like letters, and made to deliver their contents by the voce in a duplicate phonograph, every tone and expression of the writer being rendered with more or less fidelity. The phonograph has proved serviceable in recording the languages and dialects of vanishing races, as well as in teaching pronunciation. The dimensions, form, and consequent appearance of the present commercial American phonograph are quite different from that above described, but the underlying principles and operations are identical. A device for lighting gas by the electric spark is shown in figure ninety-five, where A is a flat vulcanite box containing the apparatus which generates the electricity, and a stem, or pointer, L, which applies the spark to the gas jet. The generator consists of a small influence machine, which is started by pressing the thumb key C on the side of the box. The rotation of a disc inside the box produces a supply of static electricity, which passes in a stream of sparks between two contact points in the open end of the stem, D. The latter is tubular, and contains a wire insulated from the metal of the tube, and forming with the tube the circuit for the electric discharge. The handle enables the contrivance to be readily applied. The apparatus is one of the few successful practical applications of static electricity. Other electric gas lighters consist of metal points placed on the burner, so that the electric spark from a small induction coil or dynamo kindles the jet. A platinum wire made white hot by the passage of a current is sometimes used to light lamps, as shown in Figure 96, where W is a small spiral of platinum connected in circuit with a generator by the terminals T.T. When the lamp L is pressed against the button B, the wire glows and lights it. Explosives, such as gunpowder and gun-cotton, are also ignited by the electric spark from an induction coil or the incandescence of a wire. Figure 97 shows the interior of an ordinary electric fuse for blasting or exploding underground mines. It consists of a box of wood or metal primed with gunpowder or other explosive, and a platinum wire P, soldered to a pair of stout copper wires W, insulated with gutter percha. When the current is sent along these wires, the platinum glows and ignites the explosive. Detonating fuses are primed with fulminative mercury. Springs for watches and other purposes are tempered by heating them with the current and quenching them in a bath of oil. Electrical quartery is performed with an incandescent platinum wire in lieu of the knife, especially for such operations as the removal of the tongue or a tumour. It was known to the ancients that a fish, called a torpedo, existed in the Mediterranean, which was capable of administering a shock to persons and benumbing them. The torpedo, or electric ray, is found in the Atlantic as well as the Mediterranean, and is allied to the skate. It has an electric organ composed of eight hundred or a thousand polygonal cells in its head, and the discharge, which appears to be a vibratory current, passes from the back, or positive pole, to the belly, or negative pole through the water. The gymnotus, or Surinameal, which attains a length of five or six feet, has an electric organ from head to tail, and can give a shock sufficient to kill a man. Humboldt has left a vivid picture of the frantic struggles of wild horses, driven by the Indians of Venezuela, into the ponds of the savannas infested by these eels, in order to make them discharge their thunderbolts and be readily caught. Other fishes, the Silurus, Melatururus, and so on, are likewise endowed with electric batteries that stunning and capturing their prey. The action of the organs is still a mystery, as indeed is the whole subject of animal electricity. Nobili and Mateiuchi discovered that feeble currents are generated by the excitation of the nerves and the contraction of the muscles in the human subject. Electricity promises to become a valuable remedy, and currents, continuous, intermittent, or alternating, are applied to the body in nervous and muscular affections with good effect. But this should only be done under medical advice and with proper apparatus. In many cases of severe electric shock or lightning stroke, death is merely apparent, and the person may be brought back to life by the method of artificial respiration and rhythmic traction of the tongue as applied to the victims of drowning or dead faint. A good lightning conductor should not have a higher electrical resistance than ten ohms from the point to the ground, including the earth contact. Exceptionally good conductors have only about five ohms. A high resistance in the rod is due either to a flaw in the conductor or a bad earth connection, and in such a case the rod may be a source of danger instead of security, since the discharge is apt to find its way through some part of the building to the ground rather than entirely by the rod. It is, therefore, important to test lightning conductors from time to time, and the magneto-electric tester of Siemens, which we illustrate in figures 98 and 99, is very serviceable for the purpose, and requires no battery. The apparatus consists of a magneto-electric machine A.T., which generates the testing current by turning a handle, and a Wheatstone bridge. The latter comprises a ring of German silver wire forming two branches. A contact lever P. moves over the ring and is used as a battery key. A small galvanometer G. shows the indications of the testing current. A brass sliding piece S. puts the galvanometer needle in and out of action. There are also several connecting terminals B, B1, L, etc., and a comparison resistance R, figure 98. A small key K is fixed to the terminal L, figure 99, and used to put the current on the lightning rod or take it off at will. A leather bag A at one side of the wooden case, figure 99, holds a double conductor leading wire, which is used for connecting the magneto-electric machine to the bridge. On turning the handle of M the current is generated, and on closing the key K it circulates from the terminals of the machine through the bridge and the lightning rod joined with the latter. The needle of the galvanometer is deflected by it until the resistance in the box R is adjusted to balance that in the rod. When this is so, the galvanometer needle remains at rest. In this way the resistance of the rod is told and any change in it noted. In order to effect the test, it is necessary to have two earth plates E1 and E2, one E1 that of the rod and the other E2, that for connecting to the testing apparatus by the terminal B1, figure 99. The whole instrument only weighs about nine pounds. In order to test the earth alone a copper wire should be soldered to the rod at a convenient height above the ground, and terminals screws fitted to it as shown at T, figure 99, so that instead of joining the whole rod in circuit with the apparatus only that part from T downwards is connected. The honourable R Abercrombie has recently drawn attention to the fact that there are three types of thunderstorm in Great Britain. The first, or squall, thunderstorms are squalls associated with thunder and lightning. They form on the sides of primary cyclones. The second, or communist, thunderstorms are associated with secondary cyclones and are rarely accompanied by squalls. The third, or lion, thunderstorms take the form of narrow bands of rain and thunder, for example a hundred miles long by five to ten miles broad. They cross the country rapidly and nearly broadside on. These are usually preceded by a violent squall, like that which capsized the euridice. The gloom of January 1896, with its war and rumours of war, was at all events relieved by a single bright spot. Electricity has surprised the world with a new marvel, which confirms her title to be regarded as the most miraculous of all the sciences. Within the past twenty years she has given us the telephone of Bell, enabling London to speak with Paris, and Chicago with New York. The microphone of Hughes, which makes the tread of a fly sound like the tramp of an elephant, as Lord Kelvin has said. The phonograph of Edison, in which we can hear again the voices of the dead. The electric light which glows without air and underwater, electric heat without fire, electric power without fuel, and a great deal more beside. To these triumphs we must now add a means of photographing unseen objects, such as the bony skeletons in the living body, and so revealing the invisible. Whether it be that the press and general public are growing more enlightened in matters of science, or that Professor Röntgen's discovery appeals in a peculiar way to the popular imagination, it has certainly evoked a livelier and more sudden interest than either the telephone, microphone or phonograph. I was present when Lord Kelvin first announced the invention of the telephone to a British audience, and showed the instrument itself, but the intelligence was received so apathetically that I suspect its importance was hardly realised. It fell to my own lot a few years afterwards to publish the first account of the phonograph in this country, and I remember that between incredulity on the one hand, and perhaps lack of scientific interest on the other, a considerable time elapsed before the public at large were really impressed by the invention. Perhaps the uncanny and mysterious results of Röntgen's discovery, which seemed to link it with the black arts, have something to do with the quickness of its reception by all manner of people. Like most, if not all, discoveries and inventions, it is the outcome of work already done by other men. In the early days of electricity, it was found that when an electric spark from a frictional machine was sent through a glass bulb from which the air had been sucked by an air pump, a cloudy light filled the bulb, which was therefore called an electric egg. Hit-off and others improved on this effect by employing the spark from an induction coil, and large tubes highly exhausted of air or containing a rare infusion of other gases such as hydrogen. By this means, beautiful glows of various colours resembling the tender hues of the tropical sky or the fleeting tints of the aurora borealis were produced, and have become familiar to us in the well-known Geisler tubes. Crooks, the celebrated English chemist, went still further, and by exhausting the bulbs with an improved spyingle air pump, obtained an extremely high vacuum which gave remarkable effects, page 120. The diffused glow or cloudy light of the tube now shrank into a single stream, which joined the sparkling points inserted through the ends of the tube as with a luminous thread. A magnet held near the tube bent the streamer from its course, and there was a dark space or gap in it near the negative point or cathode from which proceeded invisible rays, having the property of impressing a photographic plate, and of rendering matter in general on which they impinged, phosphorescent, and in course of time red-hot. Where they strike on the glass of the tube it is seen to glow with a green or bluish phosphorescence, and it will ultimately soften with heat. These are the famous cathode rays of which we have recently heard so much. Apparently they cannot be produced except in a very high vacuum, where the pressure of the air is about one one-hundredth millionth of an atmosphere, or that which it is some ninety or a hundred miles above the earth. Mr. Crookes regards them as a stream of airy particles electrified by contact with the cathode or negative discharging point, and repelled from it in straight lines. The rarity of the air in the tube enables these particles to keep their line without being jostled by the other particles of air in the tube. A molecular bombardment from the cathode is, in his opinion, going on, and when the shots, that is to say the molecules of air, strike the wall of the tube or any other body within the tube, the shock gives rise to phosphorescence or fluorescence, and to heat. This, in brief, is the celebrated hypothesis of radiant matter, which has been supported in the United Kingdom by champions such as Lord Kelvin, Sir Gabriel Stokes, and Professor Fitzgerald, but questioned abroad by Goldstern, Yalman, Wiedemann, Abert, and others. Leonard, a young Hungarian pupil of the illustrious Heinrich Hertz, was the first to inflict a serious blow on the hypothesis by showing that the cathode rays could exist outside the tube in air at ordinary pressure. Hertz had found that a thin foil of aluminium was penetrated by the rays, and Leonard made a tube having a window of aluminium through which the rays darted into the open air. Their path could be traced by the bluish phosphorescence which they excited in the air, and he succeeded in getting them to penetrate a thin metal box and to take a photograph inside it. But if the rays are a stream of radiant matter which can only exist in a high vacuum, how can they survive in air at ordinary pressure? Leonard's experiments certainly favour the hypothesis of their being waves in the luminiferous ether. Professor Röntgen of Vietzburg, profiting by Leonard's results, accidentally discovered that the rays coming from a crook's tube through the glass itself could photograph the bones in the living hand, coins inside a purse, and other objects covered up or hid in the dark. Some bodies such as flesh, paper, wood, ebonite or vulcanised fibre, thin sheets of metal and so on, are more or less transparent, and others such as bones, carbon, quartz, thick plates of metal are more or less opaque to the rays. The human hand, for example, consisting of flesh and bones, allows the rays to pass easily through the flesh, but not through the bones. Consequently, when it is interposed between the rays and a photographic plate, the skeleton inside is photographed on the plate. A lead pencil photographed in this way shows only the black lead, and a razor with a horn handle, only the blade. Thanks to the courtesy of Mr. A. A. Campbell Swinton, of the firm of Swinton and Stanton, the well-known electrical engineers of Victoria Street Westminster, a skillful experimentalist who was the first to turn to the subject in England, I have witnessed the taking of these shadow photographs, as they are called, somewhat erroneously, for radiographs or cryptographs would be a better word, and shall briefly describe his method. Röntgen employs an induction coil insulated in oil to excite the crook's tube and yield the rays. But Mr. Swinton uses a high-frequency current obtained from apparatus similar to that of Tesla, and shown in Figure 100, namely a high-frequency induction coil insulated by means of oil and excited by the continuous discharge of 12 half-gallon Leiden jars, charged by an alternating current at a pressure of 20,000 volts, produced by an ordinary large induction coil sparking across its high-pressure terminals. A vacuum bulb connected between the discharge terminals of the high-frequency coil, as shown in Figure 101, was illuminated with a pink glow, which streamed from the negative to the positive pole, that is to say the cathode to the anode, and the glass became luminous with bluish phosphorescence and greenish fluorescence. Immediately under the bulb was placed my naked hand, resting on a photographic slide containing a sensitive bromide plate covered with a plate of vulcanized fibre. An exposure of 5 or 10 minutes is sufficient to give a good picture of the bones, as will be seen from the frontispiece. The term shadow photograph requires a word of explanation. The bones do not appear as flat shadows, but rounded like solid bodies, as though the active rays passed through their substance. According to Röntgen, these X-rays, as he calls them, are not true cathode rays, partly because they are not deflected by a magnet, but cathode rays transformed by the glass of the tube, and they are probably not ultraviolet rays, because they are not refracted by water or reflected from surfaces. He thinks they are the missing longitudinal rays of light whose existence has been conjectured by Lord Kelvin and others, that is to say, waves in which the ether sways to and fro along the direction of the ray, as in the case of sound vibrations, and not from side to side across it as in ordinary light. Be this as it may, his discovery has opened up a new field of research and invention. It has been found that the immediate source of the rays is the fluorescence and phosphorescence of the glass, and they are more effective when the fluorescence is greenish-yellow or canary colour. Certain salts, for example the sulfates of zinc and of calcium, baryum platinocyanide, tongue state of calcium, and the double sulfate of urinal and potassium, are more active than glass, and even emit the rays after exposure to ordinary light, if not also in the dark. Sauvioni of Ferruccia has invented a cryptoscope, which enables us to see the hidden object without the aid of photography by allowing the rays to fall on a plate coated with one of these phosphorescent substances. Already the new method has been applied by doctors in examining malformations and diseases of the bones or internal organs, and in localizing and extracting bullets, needles, or other foreign matters in the body. There is little doubt that it will be very useful as an adjunct to hospitals, especially in warfare, and if the apparatus can be reduced in size it will be employed by ordinary practitioners. It has also been used to photograph the skeleton of a mummy, and to detect true from artificial gems. However one cannot now easily predict its future value, and applications will be found out one after another as time goes on. CHAPTER X Magnetic waves generated in the aether, see pages 53 to 95, by an electric current flowing in a conductor, are not the only waves which can be set up in it by aid of electricity. A merely stationary or static charge of electricity on a body, say a brass ball, can also disturb the aether, and if the strength of the charge is varied either oscillations or waves are excited. A simple way of producing these electric waves in the aether is to vary the strength of charge by drawing sparks from the charged body. Of course this can be done according to the Morse code, and as the waves after travelling through the aether with the speed of light are capable of influencing conductors at a distance, it is easy to see that signals can be sent in this way. The first to do so in a practical manner was Signor Marconi, a young Italian hitherto unknown to fame. In carrying out his invention Marconi made use of facts well known to theoretical electricians, one of whom Dr. Oliver J. Lodge had even sent signals with them in 1894. But it often happens in science as in literature that the recognized professors, the men who seem to have everything in their favour, knowledge, even talent, the men who most people would expect to give us an original discovery or invention, are beaten by an outsider whom nobody heard of, who had neither learning, leisure nor apparatus but what he could pick up for himself. Marconi produces his waves in the aether by electric sparks passing between four brass balls, a device of Professor Riege following the classical experiments of Heinrich Hertz. The balls are electrified by connecting them to the well-known instrument called an induction coil, sometimes used by physicians to administer gentle shocks to invalids. And as the working of the coil is started and stopped by an ordinary telegraph key for interrupting the electric current, the sparking can be controlled according to the Morse code. In our diagram which explains the apparatus, the four balls are seen at D, the inner and larger pair being partly immersed in Vaseline oil, the outer and smaller pair being connected to the secondary or induced circuit of the induction coil C, which is represented by a wavy line. The primary or inducing circuit of the coil is connected to a battery B through a telegraph signalling key K, so that when this key is opened and closed by the telegraphist according to the Morse code, the induction coil is excited for a longer or shorter time by the current from the battery, in agreement with the longer and shorter signals of the message. At the same time, longer or shorter series of sparks corresponding to these signals pass across the gaps between the four balls and give rise to longer or shorter series of aetheric waves represented by the dotted line. So much for the transmitter, but how does Marconi transform these invisible waves into visible or audible signals at the distant place? He does this by virtue of a property discovered by Mr. S. A. Varley as far back as 1866 and investigated by Mr. E. Branley in 1889. They found that powder of metals, carbon and other conductors, while offering a great resistance to the passage of an electric current when in a loose state, coheres together when electric waves act upon it and opposes much less resistance to the electric current. It follows that if a Morse telegraph instrument at the distant place be connected in circuit with a battery and some loose metal dust, it can be adjusted to work when the aetheric waves pass through the dust and only then. In the diagram R is this Morse receiver joined in circuit with a battery B1 and a thin layer of nickel and silver dust mixed with a trace of mercury is placed between two cylindrical knobs or electrodes of silver fused into the glass tube D, which is exhausted of air like an electric glow lamp. Now, when the aetheric waves proceeding from the transmitting station traverse the glass of the tube and act upon the metal dust, the current of the battery B1 works the Morse receiver and marks the signals in ink on a strip of travelling paper. In as much as the dust tends to stick together after a wave passes through it, however, it requires to be shaken loose after each signal and this is done by a small round hammerhead seen on the right which gives a slight tap to the tube. The hammer is worked by a small electromagnet E connected to the Morse instrument and another battery B in what is called a relay circuit so that after the Morse instrument marks a signal the hammer makes a tap on the tube. As this tap has a bell-like sound the geographist can also read the signals of the message by his ear. Two self-induction bobbins LL1, a well-known device of electricians for opposing resistance to electric waves, are included in the circuit of the Morse instrument the better to confine the action of the waves to the powder in the tube. Further the tube D is connected to two metal conductors VV1 which may be compared to resonators in music. They can be adjusted or attuned to the electric waves as a string or pipe is to sonorous waves. In this way the receiver can be made to work only when electric waves of a certain rate are passing through the tube just as a tuning fork resounds to a certain note. It being understood that the length of the waves can be regulated by adjusting the balls of the transmitter. As the aetheric waves produced by the sparks like ripples of water caused by dropping a stone into a pool travel in all directions from the balls a single transmitter can work a number of receivers at different stations provided these are tuned by adjusting the conductors VV1 to the lengths of the waves. This indeed was the condition of affairs at the time when the young Italian transmitted messages from France to England in March 1899. And it is a method that since has been found useful over limited distances. But to the inventor there seemed no reason why wireless telegraphy should be limited by any such distances. Accordingly he immediately developed his method and his apparatus having in mind the transmission of signals over considerable intervals. The first question that arose was the effect of the curvature of the earth and whether the waves follow the surface of the earth or were propagated in straight lines which would require the erection of aerial towers and wires of considerable height. Then there was the question of the amount of power involved and whether generators or other devices could be used to furnish waves of sufficient intensity to traverse considerable distances. Little by little progress was made and in January 1901 wireless communication was established between the Isle of Wight and Lizard in Cornwall a distance of 186 miles with towers less than 300 feet in height so that it was demonstrated that the curvature of the earth did not seriously affect the transmission of the waves as towers at least a mile high would have been required in case the waves were so cut off. This was a source of considerable encouragement to Marconi and his apparatus was further improved so that the resonance of the circuit and the variation of the capacity of the primary circuit of the oscillation transformer made for increased efficiency. The co-hera was still retained and by the end of 1900 enough had been accomplished to warrant Marconi in arranging for transatlantic experiments between Poldew, Cornwall and the United States stations being located on Cape Cod and in Newfoundland. The transatlantic transmission of signals was quite a different matter from working over 100 miles or so in Great Britain. The single aerial wire was supplanted by a set of 50 almost vertical wires supported at the top by a horizontal wire stretched between two masts, 157 and a half feet high and 52 and a half feet apart converging together at the lower end in the shape of a large fan. The capacity of the condenser was increased and instead of the battery a small generator was employed so that a spark one and a half inches in length would be discharged between spheres three inches in diameter. At the end of the year 1901 temporary stations at Newfoundland were established and experiments were carried on with aerial wires raised in the air by means of kites. It was here realized that various refinements in the receiving apparatus were necessary and instead of the coherer a telephone was inserted in the secondary circuit of the oscillation transformer and with this device on February 12th the first signals to be transmitted across the Atlantic were heard. These early experiments were seriously affected by the fact that the antennae or aerial wires were constantly varying in height with the movement of the kites and it was found that a permanent arrangement of receiving wires independent of kites or balloons was essential. Yet it was demonstrated at this time that the transmission of electric waves and their detection over distances of 2,000 miles was distinctly possible. A more systematic and thorough test occurred in February 1902 when a receiving station was installed on the steamship Philadelphia proceeding from Southampton to New York. The receiving aerial was rigged to the main mast the top of which was 197 feet above the level of the sea and a symptonic receiver was employed enabling the signals to be recorded on the tape of an ordinary Morse recorder. On this voyage readable messages were received from Poldew up to a distance of 1,551 miles and test letters were received as far as 2,099 miles. It was on this voyage that Marconi made the interesting discovery of the effect of sunlight on the propagation of electric waves over great distances. He found that the waves were absorbed during the daytime much more than at night and he eventually reached the conclusion that the ultraviolet light from the sun ionized the gaseous molecules of the air and ionized air absorbs the energy of the electric waves so that the fact was established that clear sunlight and blue skies though transparent to light serve as a fog to the powerful Herzen waves of wireless telegraphy. For that reason the transmission of messages is carried on with greater facility on the shores of England and Newfoundland across the North Atlantic than in the clearer atmosphere of lower latitudes. But atmospheric conditions do not affect all forms of waves the same and long waves with small amplitudes are far less subject to the effect of daylight than those of large amplitude and short wavelengths and generators and circuits were arranged to produce the former. But the difficulty did not prove insuperable as Marconi found that increasing the energy of the transmitting station during the daytime would more than make up for the loss of range. The experiments begun at Newfoundland were transferred to Nova Scotia and at Glace Bay in 1902 was established a station from which messages were transmitted and experimental work carried on until its work was temporarily interrupted by fire in 1909. Here four wooden lattice towers each 210 feet in height were built at the corner of a square 200 feet on a side and a conical arrangement of 400 copper wires supported on stays between the tops of the towers and connected in the middle at the generating station was built. Additional machinery was installed and at the same time a station at Cape Cod for commercial work was built. In December 1902 regular communication was established between Glace Bay and Poldew and it was only satisfactory from Canada to England as the apparatus at the Poldew station was less powerful and efficient than that installed in Canada. The transmission of a message from President Roosevelt to King Edward marked the practical beginning of transatlantic wireless telegraphy. By this time a new device for the detection of messages was employed as the coherer we have described in its improved forms was found to possess its limitations of sensitiveness and did not respond satisfactorily to long-distance signals. A magnetic detector was devised by Marconi while other inventors had contrived electrolytic, mercurial, thermal and other forms of detector used for the most part with a telephone receiver in order to detect minute variations in the current caused by the reception of the electromagnetic waves. With one of Marconi's magnetic detectors signals from Cape Cod were read at Poldew. In 1903 wireless telegraphy had reached such a development that the transmission of news messages was attempted in March and April of that year. But the service was suspended owing to defects which manifested themselves in the apparatus and in the meantime a news station in Ireland was erected. But there was no cessation of the practical experiments carried on and in 1903 the Cunard steamship Leucania received during her entire voyage across from New York to Liverpool news transmitted direct from shore to shore. In the meantime intercommunication between ships had been developed and the use of wireless in naval operations was recognized as a necessity. Various improvements from time to time were made in the aerial wires and in 1905 a number of horizontal wires were connected to an aerial of the inverted cone type previously used. The directional aerial with the horizontal wires was tried at Glace Bay and adopted for all the long distance stations affording considerable strengthening of the received signals at Poldew stations. Likewise improvements in the apparatus were effected at both transatlantic stations consisting of the adoption of air condensers composed of insulated metallic plate suspended in the air which were found much better than the condensers where glass was previously used to separate the plates. For producing the energy employed for transmitting the signals a high tension continuous current dynamo is used. An oscillatory current of high potential is produced in a circuit which consists of rapidly rotating disks in connection with the dynamo and suitable condensers. The production of electric oscillations can be accomplished in several ways and waves of the desired frequency and amplitude produced. Thus in 1903 it was found by Polson elaborating on a principle first discovered by Dudell that an oscillatory current may be derived from an electric arc maintained under certain conditions and that undamped high frequency waves so produced were suitable for wireless telegraphy. This discovery was of importance as it was found that the waves so generated were undamped that is capable of proceeding to their destination without loss of amplitude. On this account they were especially suitable for wireless telephony where they were early applied as it was found possible so to arrange a circuit with an ordinary microphone transmitter that the amplitude of the waves would be varied in harmony with the vibrations of the human voice. These waves, so modulated, could be received by some form of sensitive wave detector at a distant station and reproduced in the form of sound with an ordinary telephone receiver. With undamped waves from the arc and from special forms of generators wireless telephony over distances as great as 200 miles has been accomplished and over shorter distances especially at sea and for sea to shore communication has found considerable application. It is however an arc that is just at the beginning of its usefulness standing in much the same relation to wireless telegraphy that the ordinary telephone does to the familiar system employing metallic conductors. On the spark and arc systems various methods of wireless telegraphy have been developed and improved so that Marconi no longer has any monopoly of methods or instruments. Various companies and government officials have devised or modified systems so that today wireless is practically universal and is governed by an international convention to which leading nations of the world subscribe. One of the recent features of wireless telegraphy of interest is the success of various directional devices. As we have seen various schemes were tried by Marconi ranging from metallic reflectors used by Hertz in his early experiments with the electric waves to the more successful arrangement of aerial conductors. In Europe Bellini and Tosi have developed a method for obtaining directed aerial waves which promises to be of considerable utility enabling them to be projected in a single direction just as a searchlight beam and thus restrict the number of points at which the signals could be intercepted and read. Likewise an arrangement was perfected which enabled a station to determine the direction in which the waves were being projected and consequently the bearing of another vessel or lighthouse or other station. The fundamental principle was the arrangement of the antennae two triangular systems being provided on the same mast but in one the current is brought down in a perpendicular direction. The action depends upon the difference of the current in the two triangles. Wireless telegraph apparatus is found installed in almost every sea-going passenger vessel of large size engaged in regular traffic and as a means of safety as well as a convenience its usefulness has been demonstrated. Thus on the North Atlantic the largest liners are never out of touch with land on one side of the ocean or the other and news is supplied for daily papers which are published on ship-board. Every ship in this part of the ocean equipped with the Marconi system for example is in communication on an average with four vessels supplied with instruments of the same system every 24 hours. In case of danger or disaster signals going out over the sea speedily can bring sucker as clearly was demonstrated in the case of the collision between the White Star Steamship Republic and the Steamship Florida on January 26, 1909. Here wireless danger messages were sent out as long as the Republic was afloat and its wireless apparatus working. These brought aid from various steamers in the vicinity and the passengers were speedily transferred to the sinking Republic. On April the 15th, 1912 the White Star liner Titanic the largest ship afloat sank off Newfoundland after colliding with an iceberg. Wireless SOS calls for help brought several steamships to the scene and 703 persons from a total of 2,206 were rescued. On October the 9th, 1913 the uranium liner Volterno caught fire in mid-ocean and her wireless calls brought ten steamships to her aid which despite a heavy sea rescued 532 persons from a total of 657. Again on November the 14th, 1913 the Spanish steamship Balmers caught fire off Bermuda and at her wireless call the Cunard liner Pannonia saved all of her passengers 103. The Titanic horror led the principal maritime nations to take immediate steps to perfect their wireless systems and the installation of apparatus and operators soon became a prime requisite of the equipment of the world shipping. Wireless telegraphy has been developed to great efficiency in all the leading navies and powerful plants are installed on all warships. The United States, Great Britain and Germany most noticeably have established shore stations by which they can talk all around the world from any ship or station. In operation secrecy is most important for in the navy practically all important messages are sent in code or cipher under all conditions while in commercial work the tapping of land wires or the stealing of messages while illegal is physically possible for the evil disposed yet has never proved in practice a serious evil. The problem of interference however seems to have been fairly solved by the large systems though the activity of amateurs is often a serious disturbance for government and other stations. Despite the progress of wireless telegraphy it has not yet supplanted the submarine cable and the land wire and in conservative opinion it will be many years before it will do so. In fact since Marconi's work there has been no diminution in the number or amount of cables laid and the business handled nor is there prospect of such for years to come. While the cable has answered admirably for telegraphic purposes yet for telephony over considerable distances it has failed entirely so that wireless telephony over oceans starts with a more than favourable outlook. But wireless telegraphy to a large extent has made its own field and here its work has been greatly successful. Thus when Peary's message announcing his discovery of the North Pole came out of the frozen North it was by way of the wireless station on the distant Labrador coast that it reached an anxious and interested civilization. It is this same wireless that watches the progress of the fishing fleets at stations where commercial considerations would render impossible the maintenance of a submarine cable. It is the wireless telegraph that maintains communication in the interior of Alaska and between islands in the Pacific and elsewhere where conditions of development do not permit of the more expensive installation of submarine cable or climatic or other conditions render impossible overland lines. At sea its advantages are obvious. Everywhere the ether responds to the impulses of the crackling sparks and even from the airship we soon may expect wireless messages as the few untrodden regions of our globe are explored.