CHAPTER VII 



CHRONOPHOTOGRAPHY ON MOVING PLATES 

 Principles and History of the Method 



Summary. — Janssen's astronomical revolver — Muybridge's experi- 

 ments : luminous background — Photographic cameras arranged 

 in series — Control of the instantaneous shutter by electrical 

 means Photographic gun — Internal structure of the instrument — 

 Method of changing the photographic plates— Principles of 

 chronophotography on moving plates — Employment of chrono- 

 photography — Necessity for arresting the progress of the film at 

 the moment of exposure — Moment to choose for taking the 

 photograph— Form and dimensions of the photographs— Regula- 

 tion of the number and dimensions of the photographs — Repro- 

 duction, enlargement, and reduction of chronophotograjihs. 



Since the invention of photography it has served as 

 a means of comparing the present with the past by the 

 help of authentic reproductions. 



In a series of portraits taken at different periods of 

 life, anybody can see the changes wrought by time 

 upon the features of any particular face ; an engineer 

 can survey from afar the progress in the work of 

 constructing a building, and a farmer the cultivation 

 of his land. 



Mr. Janssen was the first who, for the purposes of 

 science, thought of taking by automatic means a series 

 of photographic images to represent the successive 

 phases of a phenomenon. The honour is clue to him 

 of having inaugurated what is nowadays called chrono- 

 photography on a moving plate. 



It was proposed to take a series of photographs of 



