CHAPTER III 



MOVEMENT 



Its Measurement, Graphic Representation, and 

 Analysis by means of Chronophotography 



Summary. — The understanding of a movement implies a double 

 knowledge, namely, that of space as well as that < f time — 

 Graphic representation of a movement — Chart of a tiain travel- 

 ling a ong a line — The curve of a prolonged movement should 

 hi j recorded in sections — How a moving body can record its own 

 movement — Proportional enlargement and reduction of the 

 recorded movement — Odography — Photographic record of move- 

 ment— Photography of the movement of Lippmann's electrometer 

 — Determination by means of chronophotography of the move- 

 ments executed by a fnllin^ body — Construction of the curves 

 of movement from chronophotographic images — Time-curve of 

 the distance traversed — Curve of velocity — Curve of acceleration. 



The Understanding of a Movement implies a Double 

 Knowledge, namely, that of Space as well as that of 

 Time. — We saw in Chapter II. that photography 

 could reproduce the trajectory of a body moving in 

 space ; but the idea there conveyed of the successive 

 changes in position was not sufficient to define the 

 movement. The power to do so presupposes a know- 

 ledge of the relationship existing at any moment 

 between the distance traversed and the time occupied. 

 Now, the object of Chapter I. was to demonstrate that 

 photography would permit the exact measurement of 

 time intervals. It follows that, if the two notions 

 of time and space can be combined in photographic 



