CHAPTER IV 

 CIIKONOPIIOTOGRAPHY ON FIXED PLATES 



Summary. — Object of chronophotograpliy; principles of the method: 

 measurement of time and space — Influence of the extent of 

 surface covered by the object which is to be photographed; 

 influence of the rate of movement— Geometrical chronophoto- 

 graphy — Stereoscopic chronophotograpliy— Method of multiply- 

 ing the number of images without producing confusion — Alter- 

 n.ting images - Separation of the images on the photographic 

 plate; separation by moving the apparatus — Separation by em- 

 ploying a revolving mirror. 



Since the object of chronophotograpliy is to determine 

 with exactitude the characters of a movement, such a 

 method ought to represent the different positions in 

 space occupied by a moving object, i.e. its trajectory, 

 as well as define the various positions of this body on 

 the trajectory at any particular moment. 



Let us suppose that an ordinary photographic camera 

 is directed towards a dark background, that the lens 

 is uncovered, and that a ball, brightly illuminated by 

 the sun, is thrown across the field of the objective. 

 During its passage this ball leaves an impression on 

 various parts of the sensitized plate, and on examining 

 the plate there is found a continuous curved line which 

 exactly represents the path taken by the luminous 

 ball (upper curve, Fig. 36). 



If we repeat this experiment, but only admit light 

 into the dark chamber in an intermittent fashion, and 



