76 PHOTO-TELEGRAPHY 



any other paper is, in fact, obvious. During the 

 great trial of Madame Steinheil photographs that 

 had been taken in court late in the afternoon were 

 telegraphed to London soon after 7 o'clock. The 

 time of preparation of the photographs is, of course, 

 a factor of importance ; in the earlier days it was 

 customary for an artist to draw a line sketch of the 

 photograph to be telegraphed, and this sketch was 

 then copied in the camera, and a fish-glue print 

 made from the negative on copper foil. But 

 various improvements in the apparatus have gradu- 

 ally rendered possible the transmission of half-tone 

 photographs, and thus the work of the artist is 

 done away with, together with his time. 



The preparation of these half-tone photographs 

 will be more fully considered in the chapter dealing 

 with the telectrograph, but mention may here be 

 made of the work done by M. Chatenet, which has 

 helped considerably in determining the best means 

 of producing them. 



The progress in transmission has been due, as 

 stated above, to continual small improvements in 

 the apparatus. The galvanometer is the most 

 delicate, as well as the most vital, part of the instru- 

 ment, and it is the greater perfection of the moving 

 part of the galvanometer that has contributed to 

 the improved nature of the results. 



A very small period is necessary in the " string/' 

 and its weight must be very small and its strength 



