CHAPTER V 

 THE PROBLEM OF THE GALLOPING HORSE 



UNTIL instantaneous photography was introduced, a 

 little more than twenty-iive years ago (by the dis- 

 covery of the means of increasing the sensitiveness of a 

 photographic plate), and gradually became familiar to 

 everyone in the exhibitions known as the " biograph " or 

 " cinematograph," the actual position of the legs in a 

 galloping horse at any given fraction of a second was 

 unknown. Anyone who has tried to " see " their position 

 wUl agree that it cannot be done. Attempts had been 

 made to make out what the movements and positions of 

 the legs " must " be, by studying the hoof-marks in a soft 

 track laid for the purpose. But the result was not satis- 

 factory. 



As everyone knows, the so-called "biograph" pictures 

 are produced by an enormous series of consecutive 

 instantaneous photographs taken on a continuous trans- 

 parent flexible film or ribbon. The camera has a 

 mechanism attached to it by which the sensitive film 

 is jerked along so as to expose a length of two inches 

 (the size of the picture given by the camera) for, say, one 

 thirtieth of a second without movement. The film is then 

 jerked on and a second bit of two inches is brought into 

 place for' a thirtieth of a second and so on until a ribbon 

 of some thousand pictures is obtained. The interval 

 between each picture is usually also about one thirtieth of 



