316 MOVEMENT 



I doubt whether it is possible to make a more 

 perfect zootrope, and yet there are a few defects that 

 one can mention. Firstly/ the number of images that 

 can be transferred to the disc is necessarily limited, 

 unless the apparatus is of enormous size ; and, secondly, 

 since a good definition of the movements can only be 

 obtained by very brief exposure, it follows that the 

 amount of light given off must be too small to produce 

 with distinctness an enlarged projection, and this is 

 the case even when the source of illumination is of 

 the most powerful description. 



This list of the different forms of apparatuses used 

 in the synthesis of movement is, no doubt, incomplete ; 

 but it may serve to indicate the respective advantages 

 and disadvantages of each system, and to serve as a 

 guide to those who may wish to make fresh researches 

 in the same direction. 



The Points of a Good Apparatus. — In apparatuses in 

 which the figures rotate with a continuous movement 

 the image can only be made to appear motionless by 

 giving such a short exposure that the movement 

 during that time is inappreciable. 



Now, the brevity of the period of illumination 

 entails a considerable loss of light, and hence the 

 image, when projected on a large scale, is hardly 

 visible at all. If, on the other hand, it is necessary 

 to produce a brilliant projection, the duration of the 

 exposure must be as long as possible ; in that case, 

 however, the image which is for the time being under 

 observation must be absolutely motionless. It is 

 obviously impossible to ensure alternate periods of 

 rest and motion with discs or other heavy pieces 

 of revolving apparatus. The solution of this pro- 

 blem is the same as that which we adopted in 

 chronophotogiapliy. The apparatus which is used 

 for the analysis of movement is reversible, at least in 



