io6 



PHOTO-TELEGRAPHY 



electrical impulses are of far longer duration, and 

 represent small parts of a picture instead of vocal 

 sounds. 



As the function of the transmitting instru- 

 ment is merely that of an interrupter, it is 



clear that the sending bat- 

 tery can be included in the 

 receiving station, hence a 

 portable apparatus is not 

 impossible. Portable instru- 

 ments are now, as a matter 

 of fact, being constructed, 

 in which the motive power is 

 derived from a particular form 

 of clockwork mechanism. 

 The portable machine is the 

 key to general commercial 

 utility, and its developments 

 will be watched with interest. 

 One drawback to the 

 telectrograph, viz., that a 

 negative image had to be 

 used on the transmitting 

 cylinder instead of a positive (the latter being more 

 easily and rapidly prepared), has recently been 

 overcome. A positive print having about fifty lines 

 to the inch is used, and at the receiver a current is 

 passed through the electrolytic paper which con- 

 tinuously discolours it. The currents transmitted 



FIG. 49. M. Riolle, Public 

 Prosecutor in the Stein- 

 heil case ; wired from 

 Paris to London by the 

 Thome - Baker Telec- 

 trograph. 



