Page:Popular Science Monthly Volume 52.djvu/197

Rh 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 attempted 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 noticeable; 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 intervals 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 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 uniform illumination is essential, it would be necessary to exclude daylight 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"