12 THE MECHANISM OF 



A piece of catgut arrests the action of the spring without 

 drawing taut the adjusted strings which pull down the slides. 



The closed circuit was used for the shutter, that no time should 

 be lost by the magnet reaching for the armature and because less 

 battery power would be required. 



In the camera a new precaution was taken against extraneous 

 light, — a moving diaphragm immediately in front of the plate, 

 and connected with a peep-sight above the camera. An assistant 

 having adjusted the diaphragm somewhat larger than the image 

 to be photographed, and having placed his eye to the hind sight, 

 follows the moving object by keeping it between the two front 

 sights, the front sights being at a distance from the hind sight 

 equal to the conjugate focus of the lens. 



The plate itself can also be slid right and left by the frame 

 which carries it, in case successive poses may be executed in one 

 place and their images are desired on one plate. 



To increase the range of the instrument, a second camera was 

 devised for investigating the class of movement in one place, as 

 that of a man throwing a stone, where, in the Marey camera, the 

 images would superimpose. 



In this camera the plate is revolved on a frame at the end of 

 an axle, which pierces the back of the camera. 



Belting and pulleys connect the movement of the disks and 

 of the plate, and a pair of friction-wheels allows such an ad- 

 justment of speed from the disks to the sensitive plate that the 

 images may be made just to clear one another. 



To use this camera the ground glass is set true by adjusting 

 screws and the lens focused. A ten by twelve inch plate or 

 smaller is cut to an octagon and replaces the ground glass, being 

 sprung up against the adjusting screws. The distance of the 

 images apart having been determined upon in degrees when the 

 ground glass was in, the speed of the plate is now adjusted. A 

 style on the armature of an electro-magnet in the exposure- 

 counting circuit dots on a smoked disk, whose rim is graduated, 

 the different exposures as the machine is turned. The sliding- 

 bar carrying one of the friction-wheels is pushed in or out until 

 the dots become the requisite number of degrees apart. 



A moving diaphragm is also attached to this camera, having a 

 slight horizontal movement and governed by a peep-sight. 



