LINES IN PHOTOGRAPHS 51 



ingly good photograph, eminently suited to 

 the selenium process, and it is a peculiar 

 fact that, as far as an actual face is con- 

 cerned, that photograph still remains the most 

 perfect ever transmitted, putting aside the purely 

 technical peculiarity of the stripes or bands of which 

 it is composed. These lines in the photograph 

 correspond to the threads of the screw axle ion which 

 depends the upward travel of the receiving drums, 

 and they make an angle with a line drawn hori- 

 zontally across the greatest length of the picture of 



approximately sin~ J (-p-l. The lines can be got 



rid of by placing the small lens which concentrates 

 the light from the triangular diaphragm upon the 

 film at a greater distance from the film, but the 

 sharpness of definition of the photograph then at 

 once suffers. This may sometimes be all the better 

 in the case of a portrait where the diffusion renders 

 the result much more " photographic/' But the 

 sharpest definition is necessary where any attempt is 

 made to telegraph a picture with any small detail 

 in it. " Small detail " is in itself a limited term, 

 as only very bold and simple subjects can be trans- 

 mitted with apparatus of this size, and hence its 

 almost exclusive application to the telegraphy of 

 portraits. The lens above referred to should cast 

 an image of the triangular aperture on the film 

 which is almost a point. 



E 2 



