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Psychological Investigations   229

time was a bold proposal, that all anthropologists should turn for a time from physical anthropology and study prevalent types of human character and temperament. He points out how it has now become possible to inquire by exact measurement into certain fundamental qualities of the mind; the new science of what has been termed Psychophysics shows that the difference in the mental qualities of man and man admits of being gauged by a suitable scale. Galton further suggested that mental qualities such as `personal equation' and its basis in reaction time should be measured with a view of correlating them with temperament and external physical characters. Among other things he suggests the classification of individuals by the time they occupy in forming a judgment. He notes that the interval of time between the perception • of a signal and the recording of it by tapping a key, is modified when there are alternative signals A and B, and the recording of A is to be done by the right and of B by the left band. An interval is required to discriminate between the signals and between the hands. In such a way the individual time in forming a judgment can be to some extent measured. Galton compares the advance of that day in the measurement of mental characters with the numerical measurement by the thermometer of heat and cold in the days of old. As Dr John Beale wrote to Boyle in 1663:

"If we can discourse of heat and cold in their several degrees so as we may signify the same intelligibly ... it is more than our forefathers have taught us to do hitherto."

The pity is that so much psychometric apparatus is far more expensive than thermometers ! If we can, however, obtain a group with differentiated mental characters, how shall we ascertain the external physical features most commonly associated with its members? And here Galton turns, I think for the first time, to photography for assistance.

He suggests, in the first place, a standard form of photography in which by the aid of three mirrors, a direct three-quarter face, and reflected profile, full-face and top of head aspects would be obtained on the same plate at the same time. Unfortunately he does not describe adequately the positions of these mirrors, and I have been unable to determine them. I can get by reflection norma facialis, norma lateralis and norma verticalis (as they are termed in craniometry), but then the direct aspect appears to be a threequarter occipital view ! Galton next makes what I believe is his first announcement as to composite photography; that is the method he proposes of ascertaining whether those with differentiated mental characters have differentiated physical features. He writes:

"Having obtained drawings or photographs of several persons alike in most respects but differing in minor details, what sure method is there of extracting the typical characteristics from them? I may mention a plan which had occurred both to Mr Herbert Spencer and myself,

the principle of which is to superimpose optically the various drawings and to accept the aggregate result. Mr Spencer suggested to me in conversation that the drawings reduced to the same scale might be traced on separate pieces of transparent paper and secured one upon

sweeter my temper is likely to be.-He is such a choice specimen of the Snob scientific." X. is dead now, without leaving his impress on science, but the term Huxley found' in his wrath to characterise the young gentleman is perhaps worthy of preservation.