CH. IX 



CONTROL 



207 



of 300, 400, 500, and 600 feet, we get the results shown in 

 the following table : 



We see that when the distance is greater than 300 

 feet, the difference in time between the 100 and the 50 

 ampere arrangement is constant, and equal to seven 

 seconds. The actual difference in the energy increases 

 slightly with the distance, the smaller current involving 

 a greater expenditure of energy; but the percentage 

 difference remains very nearly the same at all distances. 



Since the difference in time for a given distance 

 becomes constant, it follows that the difference in energy 

 must also become constant. This would be clearer if the 

 current curves were continued to the point at which they 

 coincide ; we should then see that the difference in the 

 shape of these curves was only at the beginning, and that 

 an increase in the distance travelled simply means adding 

 an equal area to each. 



We may think of two cars on parallel lines started up 

 at the same moment, one taking 100 and the other 50 

 amperes. The former will start off quicker, but in time 

 they will both attain the same speed, and the former will 

 then keep seven seconds ahead of the latter. The difference 

 in the energy for any given distance is evidently the 

 difference occasioned during the period of starting. 



