SYNTHESIS OF MOVEMENT 317 



principle, and might be used for their synthetic re- 

 construction. Let us imagine that a strip of film has 

 imprinted on it positive images, and that this strip 

 is placed at the focus of the object-glass, and brightly 

 illuminated from behind. If these figures are then 

 projected on a screen as far removed from the object- 

 glass as were the original objects, the figures will 

 appear to actual scale. 



Every time the objective is exposed by the rotation 

 of the diaphragm an image is thrown on the screen, 

 the outlines of which are perfectly defined, because 

 the film is arrested by compression at the moment 

 of exposure. As a matter of fact, it is better to adopt 

 a special contrivance for projecting moving figures. 



The following are the reasons which induced us to 

 construct a new instrument, to which we have given 

 the name, " Chronophotographic projector." 



The Chronophotographic Projector. — In a projecting 

 apparatus the exposure should be as long as possible, 

 and the transparency should be arrested during the 

 whole period of its projection upon the screen. These 

 conditions must be fulfilled if bright and clear images 

 are required. In the case of the analyzing apparatus, 

 the exposures, on the contrary, should be as brief as 

 the illumination will allow. For an insect's wins:, 

 the exposure should be no more than 25000 P art 

 of a second. Xow, with such a short exposure, an 

 image would be almost invisible if greatly enlarged by 

 projection ; and this would still be the case even 

 were the source of illumination very powerful. The 

 most important point in constructing a projector is 

 to secure as long an exposure as is possible. For 

 instance, if ten images were taken per second, the 

 exposure should be half or a third as long ; that is 

 to say, for ^0 or 30 °f a second, instead of for j-^qq of 

 a second, which is the usual exposure allowed by 

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