MOVEMENT 



35 



Time in minutes 

 c i" 2- y w 5' 



I, 



between the visible point and the sensitized plate on 

 which from moment to moment its movement is 

 recorded. To fully appreciate the advantages of 

 chronophotography, it will doubtless be best to 

 compare it with other methods already employed in 

 the solution of the same problems. Let us take the 

 most simple case, that of recording the displacement 

 in a straight line of a moving body, and let us 

 approach the question in accordance with the two 

 methods. 



Graphic Representation of Movement. — When a point 

 travels along a straight line, the successive positions 

 can be indicated by means of two straight lines at 

 right angles to one another. 

 These two straight lines, the 

 one horizontal and the other 

 vertical, indicate respectively 

 the time taken and the dis- 

 tance traversed. If the mov- 

 ing body is propelled at a 

 uniform rate of one hecto- 

 metre to the minute, this 

 movement can be expressed 

 by the oblique line which joins 

 the points where the divisions of time and space 

 intersect (Fig. 25). This is the curve of movement. 

 In the case of a uniform movement, this line is 

 always straight : but it will be more or less obliquely 

 inclined according to the speed at which the body 

 travels. Thus, for double speed, that is to say, two 

 hectometres in the minute, the line will pass through 

 the point at which the second division of space and 

 the first division of time intersect. It will thus form 

 the diagonal of a series of rectangles, the sides of 

 which will be formed of two space-divisions and one 

 time-division. This system of representation expresses 



Q 6 



Fig. 25. — Graphic representation 

 of a uniform movement. 



