Practical cinematography and its applications (1913)

i8 PRACTICAL CINEMATOGRAPHY advance like automatons. Again, in photograph- ing animals, a complete movement is often lost between successive pictures. A cat in one pic- ture will be seen to the right; in the next picture it is on the left, having sprung from one side to the other during the brief interval the lens was closed. When extremely rapid movements have to be recorded, the photographing speed has to be accelerated to an extreme degree, up to ten thousand pictures or more per second in the case of a bullet leaving the muzzle of a rifle, and up to two thousand pictures per second to catch the move- ments of a dragon-fly's wings. On the other hand, in photographing very slow movements like the growth of a plant, one picture per hour may be adequate. In projection the speed can be adjusted. The ten thousand pictures per second may be de- celerated to sixteen per second to allow the movement to be followed, and although the rifle bullet may appear to crawl through the air, the movement is perfectly correct. Similarly the very slow motions must be accelerated to sixteen pictures per second to obtain evident anima- tion. These two extreme phases of cinemato- graphic investigation are described at length in another part of this volume, but are mentioned here merely to show that the photographing speed is a somewhat elastic factor, to be adapted