Pholoiiraphlc Rfnenrches aiuf Port rait it re 



289 



for all subjects, but the distance from iriterpupillary line to the line of 

 the lips is also made constant'. The general principle of the ap{)anitu8 

 is that of a modified copying-camera, only the alteration in scale and the 

 adjustment in position are not done on the focusing-screen, because it is 

 desirable that the negative which is to be several times exposed should 

 remain fixed in position. By the simple artifice of a mirror let down at 45° 

 across the camera, Galton gets an image on a horizontal screen in the ro<jf 

 of his camera, and upon this screen also are thrown the three fiduciary linens 

 which serve ius register-marks for his adjustments. The details of the 

 apparatus will Ir' sufficiently indicated by the accompanying line engraving 

 and (Talton's description of it ; we may merely remark that gas would 

 now-a-days be prol)ably replaced by electric light. The apparatus is still 

 preservea in the Galton Laboratory. 



Diagram showing thr Essbntial Parts. 



A The body u. .... ^..uiora, whiob is 6xed. 



B Lens on a carriage, which can be moved 

 to and fro. 



C Frame for the transparency, on a oar- 

 riaKe that also supportR^the lantern ; the 

 whole can be moved to and fro. 



r The reflector inside the camera. 



Ill The arm outside the camera attached to 

 the axis of tho reflector; by raovinR it, the 

 reflector can be moved up or down. 



(/ A ground'glas!) screen on the roof, which 

 receives the image when the reflector is 

 turned down, as in the diagram. 



The eye-hole through which the image ia 



viewed on u; a thin piece of glam im- 

 mediately below e reflects the illuminated 

 fiducial lines in the transparency at /, 

 and gives them the appearance of lying 

 upon g — the distances /k and gk being 

 made equal, the angle fkg being made a 

 right angle, and the plane- of the thin 

 piece of glass being made to bisect /kg. 

 Framework, adjustable, holding the trans- 

 parency with the fiducial lines on it. 

 Framework, adjustable, holding the trans- 

 parency of the portrait. 



Diagram ii. 



" For success and spee<l in making composites, the apparatus should be solidly made, 

 chieHy of metal, and all the adjustments ought to work smoothly and accurately. Good com- 

 posites cannot he made without very careful adjustment in scale and position. An oflThand 

 way of working produced nothing but failures." (p. 143.) 



Galton exhibited certain results of very considerable interest tending to 

 meet critici-sms which had been raised. He drew on a square card a circle 

 of about 2 '5 inches diameter with a vertical and a horizontal diameter. 

 Where these diameters met the circle he placed four circular discs of different 

 tints, and in one quadrant he placed a black dot. He then made a composite 



' It would probably be possible by a slight rotation of the frame for the transparency 

 about a central vertical axis to make the interpupillary di.stance (or the external ocular 

 distance) constant without in any way injuring the result. 



P o II 37 



