INSTANTANEOUS PHOTOGEAPHY. 29 



the arm B and at the same time throwing it into gear with the 

 rotating shaft. The brush is thus carried around over the ring S^ 

 and as it makes contact with each segment, a current passes through 

 the three exposor magnets of the same number and through the 

 chronograph magnet, and exposures are made synchronously from 

 the three points of view. With the brush in the positions shown 

 by full lines in the diagram we can follow the course of the 

 current ; from the negative pole of the battery C to the binding- 

 post U, thence to the stationary brush K in contact with B^ 

 through B and the rotating brush to segment No. 2, from tliere 

 through E, to binding-post P 2, where it separates into two parts, 

 one passing through exposor magnet L 2, and back to P, R, the 

 other to double binding-post D 2, where it subdivides into two 

 parts, passing through exposor magnets E 2, and F 2, respectively^ 

 and back through D, R, to P, R ; from P, R, the entire current 

 returns to the positive pole of the battery C, after passing through 

 the chronograph magnet e, m, and thereby making a record of that 

 exposure on the drum J. 



The way in wiiich the contact-brush is automatically thrown 

 into gear with the revolving shaft can be seen by reference to the 

 diagram of " mechanism for starting contact-brush" (Fig. 2), where 

 some of the revolving parts are drawn in vertical section to show 

 the internal construction. The shaft / is bored hollow for a part 

 of its length, the internal diameter being smaller near the bottom 

 of the bore than it is towards the end of the shaft. Into the 

 bore fits a spindle, S, whose external diameters correspond to the 

 internal diameters of the shaft. To the spindle S is keyed a 

 collar, O, in whose outer face radial teeth are cut. The key V 

 passes through a slot in the shaft F, so that the spindle S, with 

 the collar O, can be moved in or out for a short distance, limited 

 by the length of the slot, while at the same time it will be noticed 

 S and O will be carried around with / when it revolves. Loose 

 upon / is a second collar, n, which carries the double arm d with 

 the contact-brush, and has on its inner face radial teeth to gear 

 into those in o. In the space inside the shaft, between the shoul- 

 ders in / and that in s, a coil spring is fitted, which pushes the 

 spindle outward, throwing o into gear with n, unless prevented 

 by resistance at the conical extremity of s. Such resistance is 

 offered by the upper arm of a bent lever, I, whose lower arm fits 



