294 MOVEMENT 



accompanies this light would soon destroy the living 

 creatures which move about in the preparation. The 

 employment of vessels containing a solution of glycerine 

 and alum has been regarded as the best means of 

 arresting caloric rays ; it is, however, altogether in- 

 efficient, and so we have resorted to a special arrange- 

 ment of our own. Instead of allowing the light to 

 shine continuously on the preparation, it was projected 

 in an intermittent fashion, and only allowed to act for 

 a very short duration, generally less than xoVo P ar ^ °f 

 a second. 



By this method, no matter how great the condensa- 

 tion of the heat, it could never inflict an injury on 

 the creatures under observation. 



Chronophotography lends itself most happily to 

 these instantaneous illuminations. 



It is quite sufficient to place the object under 

 examination behind the circular diaphragms. The 

 function of those discs from that time forward is to 

 intercept the luminous rays, which would otherwise 

 reach the preparation, and only to illuminate the 

 latter during the short intervals when the fenestra- 

 tions in the two diaphragms coincide. 



Fig. 200 shows the principal parts of the special 

 apparatus which is adapted to the chronophotographic 

 camera for the analysis of microscopic movements. 



A wooden box with a central aperture slides into 

 the front part of the apparatus like the frame for 

 containing the object-glasses which has already been 

 described. 



This box contains an object-glass, C, in its anterior 

 portion for condensing the light which reaches it from 

 the heliostat. The focus of this condenser is arranged 

 so as to fall upon the plate p, at the same spot at 

 which the preparation is to be placed. During the 

 process of focussing, the position of the plate carrier 



