ANIMATED PICTURES. 183 



another, while the rapid fading of these retinal impressions gives rise 

 to the pulsating effect that is familiar to everybody. 



Now, the well-known optical phenomena which I have here at- 

 tempted to describe are, in fact, closely analogous to those exhibited 

 by the animated pictures.* In the former case we have to deal 

 with a moving body; in the latter, with photographs of such bodies; 

 and since the momentary images in the first-mentioned case are 

 practically changeless, it is evident that a similar general effect must 

 be produced upon the organ of vision. 



We have hitherto been concerned with motion pictures of the 

 ordinary type — those, namely, which reproduce with accuracy the 

 movements of the original scenes. In order to secure this result 

 it is essential that our pictures be " taken " and exhibited at the 

 same rate per unit of time. Where this condition has not been 

 fulfilled, it is manifest that the pictured objects must appear to 

 move either quicker or more slowly than their originals. If 

 the difference in rate be small, its results will hardly be notice- 

 able; if large, a curious but awkward and unnatural effect will be 

 produced. 



Suppose now the mechanism of our camera to be altered in such 

 wise that successive exposures may be made at relatively long inter- 

 vals of time, while the duration of each exposure can be varied at 

 will. With this end in view, the camera should be provided with 

 clockwork capable of running for twenty-four hours continuously. 

 Thus equipped, we should be ready to experiment on objects — such 

 as growing plants — whose changes are of too gradual a nature to be 

 perceived by the eye. 



An ordinary house plant — let us say a geranium, abutilon, or 

 hyacinth — would form an admirable subject for the purpose. The 

 photographs might be taken under the electric light f at intervals 

 of an hour or more, though plants of rapid growth (such as climbers) 

 might well be photographed at much shorter intervals. As a uni- 

 form illumination is essential, it would be necessary to exclude day- 

 light while taking the negatives. At night the light source could 

 be maintained continuously — a condition which tends, as is well 

 known, to stimulate the growth of plants. The experiments might 

 extend over a period of weeks, or even of many months, according 

 to the nature of the plant selected. But the resulting film, when 

 placed in the cinematograph for exhibition, would be " reeled off ' 



* The analogy will be rendered more exact if we assume that one eye only is used by 

 our observer in viewing the moving object. Binocular vision would modify, to a perceptible 

 extent, the appearances presented. 



f An incandescent lamp would probably give the best results, though gas or oil flames 

 could evidently be utilized. 



