14 



THE MECHANISM OF 



The exposure-counting circuit possesses another device. 



On top of the first camera described, where a peep-sight carrying 

 the diaphragm follows the movement, are two parallel strips of 

 metal on wooden slides. They are so slid past one another that 

 the length of metal opposite may equal the length of the photo- 

 graphic plate used. The peep-sight bar carries a bridge clamped 

 at pleasure, springing its contact points from one to the other 

 slide, so that the circuit passing this bridge may not count images 

 that might occur where there is no plate to receive impressions. 



The battery used was composed of eight Le Clanche cells. 

 Two, three, or four cells in series are thrown by a switch into 

 the fork, or time-circuit. 



Two cells are used for the exposure-counting circuit, and one 

 cell for each shutter-slide, eight in all, and a ninth cell is in re- 

 serve to replace or reinforce any one that might accidentally give 

 out. The lens used was a Ross carte-de-visite lens of six and 

 three-quarter inches equivalent focus. It is to be regretted that 

 Professor Eakins's admirable work is not yet sufficiently com- 

 plete for publication as a whole. 



Fig. 3. 



The reproduction of a boy jumping horizontally, shown above, 

 which Professor Eakins has photographed on a single plate by 



