:]1»J Life antl Litters of Frnncin Galton 



"But neg&tiveM and positives do not wholly obliterate one another. They do ho to all intents 

 and pur|>06eii when the tones are not very far from the middle of the Hcale; an extreme white 

 is not obliterated by its negative." (p. 137.) 



Galton was 78 years of age when the paper was published, and it was 

 hurriedly written (p. 138). He never worked out the technique with the care 

 and elalwration he devot«d to composite portraiture. Yet it seems to me that 

 the niethtxl is capable of Ijeing developed, and if it were the results re^iched 

 by it would be of very great value. The key to the whole position is the 

 production of a perfectly obliterating positive and negative pair. Galton's 

 original suggestion that 



"the only satisfactory experiments now would be those made by two converging lanterns on a 

 screen, one at least of which admits of easy and delicate adjustment in direction and intensity 

 of it« illumination"' 



might still be of aid in the matter. It is possible that the use of homogeneous 

 light in the preparation of both positives and negatives might be of some 

 value. Anyhow I peixonally should be sorry to dismi.ss analytical photo- 

 gi-aphy as idle. From the psychological standpoint it ought to be of first 

 class value in the study of the expression of the emotions. It should indicate 

 what physical or muscular changes accompany such expression. The subject 

 needs to-day an enthusiastic cultivator, who has the patience to develop its 

 technique. 



{D) Measurements by Photography. 



In 1896 Francis Galton started another incjuiry. He appears fii-st to have 

 developed a scheme for taking from the same spot two photographs, one with 

 the camera horizontal and the other with the camera tilted. By aid of two 

 such photographs distances were to be measured photographically. The 

 method of reduction is in some way Jissociated with photographs (positive and 

 negative) of a horizontal ruled square divided up into 20 x 20 small squares. 

 The two chief diagonals are marked and there are posts on the scjuare at the 

 centre and the corners. It was apparently capable of rotation about the centre 

 and there are photographs of it with the optical axis of the camera in one of the 

 diagonal planes, and in a plane bisecting the diagonal planes. There are photo- 

 graphs of streets, roofs and chimneys seen from a high parapet, possibly of 

 a briflge, apparently to be used in testing the method. But the manner in 

 which the reticulation was to be used in these cases is very obscure, and so far 

 I have only foiuid the box of negatives, and no explanatory notes or papers, 

 in the (Jaltoniana. It would be rash to make any dogmatic assertion, but it 

 would appear as if Galton at a fairly early date had been indejjendently 

 working at photographic triangulation. 



Photographic Measurement of Distances and Lengths. No less than 

 eleven notebooks in the Galtoniana deal with this topic. They appear to 

 have Ijeen stalled in 1894-1895. They contain not only expernnental 

 measurements, but a succession of drafts of pa])er8, changing sometimes by 



' Nature, Vol. I.X1I, p. 320. Attempts in this direction would have been made before this 

 in the Ualton Laboratory, but for inadequacy of funds. 



