STA



Parallel motion, by Watt, lag

theory of, 130-4

of beam engine, 137

of marine engine, 138

application of, 139

in grashopper engines, 142

in compound engines, 146

— — in Richards' indicator, 261
Paul, meaning of term, 150

— action of, 151

Pauls, of unequal length, 153

— application of, 154
Peaucellier's straight line motion, 143
Pendulum, simple, 60

— law of oscillation, 60

— centre of oscillation of rigid, 61

— model to illustrate same, 62

— mechanical action of, 65
Pin wheels, theory of, 179
Pinion, meaning of term, 22

— lantern, 179
Pitch, diametral, 168

— circular, 169

Photometer, Wheatstone's, 177
Planing machine, reversing motion, 89

feed motion, 157

Plimpton's roller skate, 338

Point, motion of a, 4
• — circular motion of, 9

— harmonic motion of, 9

Power, telodynamic transmission of, 29
Ptilley, convex rim of, 26

— single movable, 219
Pulleys, fast and loose, 27

— with inclined axes, 28

— guide, 30

— speed, 196

— theory of same, 197

— applied in lathe, 199

— conical, 200



"D ACK and pinion, forms of teeth, 182

-'-^ teeth derived from involute

of circle, 188
Rack, mangle, 105

— double, 108, 216
Ratchet wheel, 150

for driving in alternate directions,

used in lifting jack, 152

— — vrith click and hook, 162
masked, 163-5

compared with lifting pump, 167

Ratchet brace, 152

Reciprocating into circular motion, 148

— examples, 166
Rectangular bars, 273



Reversing motion, by spur wheels, 85

with quick return, 86, 88

example of, 87

by disc wheels, 90

— ^- by bevel wheels, 91
by clutch, 91

adopted by Sir J. Whitworth, 92

example in rifling machine, 94

by pulleys and belts, 96

by slit bar and crank, 97

theory of same, 97-ior

by double eccentric and link motion,

318^3
Roberts's winding-on motion, 303
Rolling curves, theory of, 324

examples, 325

for quick return, 327

in printing machinery, 32B

Root's blower, 313
Rope, twist of, 24s

— model to illustrate same, 247

— extra twist, apparatus for, 248



SAXTON'S differential pulley, 217
Scraping tool, 269
Screw surface, definition of, 34
Screw, pitch of, 34

— right or left handed, 34, 207

— single or double threaded, 33
Screw threads, 34

mechanical properties of, 34-6

uniform system of, by Sir J. 