22 



THE MECHANISM OF 



spaces in the front, and by focusing it all of the lenses are 

 focused simultaneously. Three plates, twelve inches long, fill 

 the one plate-holder (Fig. 9) that is used for the whole battery. 

 It can now be understood that there is a great saving of time in 

 the use of these cameras, due to the method of focusing, and to 

 having to fill, empty, and draw the slide of only one plate-holder 

 instead of twelve for each series of photographs. 



Fig. 9. 



nliniwiliiliiiinlninMliinlUiiliniuiiiiu ui u ii nuinmiWimil IllllJillJiJIIIIIIIIII nil M'll 



iiiiiiiipTi nn ii'' m ii m iii T 7 '' ;r ''^ ^ ^ 



f\ I I I |i .! 11 i| ii " 



The dark room at the studio in which the plate-holders Avere 

 filled and emptied was situated at the western end of the camera- 

 house, at V, Fig. 1. It was of necessity absolutely dark, ex- 

 cepting the few colored rays which came through a window of 

 ruby glass covered with dark orange paper; for the dry plates 

 used by Mr. Muybridge were the most rapid he could obtain, — an 

 extra-sensitive emulsion prepared especially for him by Cramer, — 

 and the slightest premature touch of white light w^ould have 

 fogged them. The greatest care was therefore necessary in han- 

 dling the plate-holders outside. They were carried to and from 

 the dark room each one in a thick black cloth bag, which was 

 removed only under the focusing-cloth of the camera. 



Successive exposures were made by sending the electric current 

 through the releasing magnet of each exposor in a series succes- 

 sively, at intervals varying according to the rapidity of the 

 motion photographed. In the California experiments the circuit 

 for each magnet was usually made by the contact of metallic 

 springs, caused by the subject running against and breaking a 

 series of fine threads stretched perpendicularly across the track in 

 front of each camera. But this method, though a very ingenious 

 one, had its disadvantages for the work in Philadelphia. Much 



