Photographic Researches and Portraiture 317
very little the method of procedure, or changing sometimes its applications. There are a good many negatives or prints also referring to the matter, some intelligible, some needing an interpretation, which I have been unable to supply. To one series of such, clearly involving distant objects, I have already drawn attention (see p. 316) ; a good deal of the matter refers to fairly near objects, and the first experit'`nents-to judge by the photographs-seem to have been made on a series of shelves or racks at the Kew Observatory. Then Galton photographed a bronze horse (Carousel) and determined the three coordinates of eight to eleven points of it in a. variety of ways. It is really wonderful thirty years later to see the amount of labour he put into work of this kind. A reader of Nature might conclude that his communications to it were brilliant suggestions written in a few hours. This, I believe, was never the case; he rarely refers to a tithe of his experimental work, the calculations, trials and failures he had made before preparing his paper; in many cases a paper was written over and over again before it assumed its final form, and if a reader of the latter thinks the result could have been more easily reached by another method, it is extremely probable that that method could be found, experimentally tested and silently rejected, in one or other of Galton's preliminary notebook records. If he tried and condemned a method, he scarcely ever stated that he had done so. He assumed that his readers would suppose him to have surveyed the country before plotting the selected path to his goal.
Galton started with the general problem of studying the perspective of a photograph; he did this by the simple method of photographing with his subject some horizontal reticulation, or if needful both a horizontal and a vertical reticulation, and this served as the basis for analysing the perspective properties of the photograph. Galton shows that photographic measurements of objects may be divided into two classes; those in which we measure lengths parallel to the focal plane of the camera, and those in which we measure other lines, and in this case we may require two photographs of the same object taken simultaneously from different aspects. The mathematics of the latter are by no means complicated, and are provided by Galton, but his dominant passion for the study of heredity soon led him to the measurement of animals, and by proper orientation of the animal the principal measurements Galton was seeking can be obtained from a single standardised photograph, provided it is accompanied by suitable reticulations or fiducial lines.
In one of his many notebooks I find the draft of a paper which starts thus:
"Architectural draughtsmen are familiar with the art of translating objects into their perspective representations, but the converse process of translating perspectives into their objective equivalents has never, I believe, been yet brought-into practice'. So long as pictures had to be
' It was not an uncommon problem before even 1890 to ask engineering students to draw a model in perspective and then take the measurements of parts of the original model from the perspective drawing. It must be confessed, however, that it was done with the view of testing drawing accuracy and possibly suggesting the superiority of plan and elevation drawings. It would certainly have been good experience to have obtained measurements- of the parts of machines by double photographs of them accompanied by suitable reticulations.