F. Galton—Address before the British Association. 269 
The principal experiments by which the mental faculties ma 
be measured require, unfortunately for us, rather costly and del- 
icate apparatus, and until physiological laboratories are more 
numerous than at present, we can hardly expect that they will 
be pursued by many persons, 
us now suppose that, by one or more of the methods I 
have described or alluded to, we have succeeded in obtaining a 
group of persons resembling one another in some mental qual- 
ity, and that we desire to determine the external physical char- 
acteristics and features most commonly associated with it. I 
have nothing new to say as regards the usual anthropometric 
measurements, but I wish to speak of the great convenience of 
photographs in conveying those subtle but clearly visible pecu- 
liarities of outline which almost elude measurement. It is 
strange that no use is made of photography to obtain careful 
studies of the head and features. No single view can possibly 
exhibit the whole of a solid, but we require for that purpose 
views to be taken from three points at right angles to one an- 
other. Just as the architect requires to know the elevation, 
side view, and plan of a house, so the anthropologist ought to 
have the full face, profile, and view of the head from above of 
the individual whose features he is studying. f 
It might be a great convenience, when numerous portraits 
have to be rapidly and inexpensively taken for the purpose of 
anthropological studies, to arrange a solid framework support- 
ing three mirrors, that shal] afford the views of which I have 
been speaking, by reflection, at the same moment that the di- 
rect picture of the sitter is taken. He would present a three- 
quarter face to the camera for the direct picture, one adjacent 
mirror would reflect his profile towards it, another on the oppo- 
site side would reflect his full face, and a third sloping over 
him would reflect the head as seen from above. All the re- 
flected images would lie at the same optical distance from the 
camera, and would, therefore, be on the same scale, but they 
would be on a somewhat smaller scale than the picture taken 
directly. The result would be an ordinary photographie pic- 
ture of the sitter surrounded by three different views of his 
head. Seales of inches attached to the framework would ap- 
pear in the picture and give the means of exact measurement. 
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 ee occurred both to Mr. 
Herbert Spencer and myself, the principle of which is to super- 
impose optically the various drawings and to accept the aggre- 
gate result. Mr. cer suggested to me in conversation that 
the drawings reduced to the same scale might be traced on sep- 
