ON RAILWAY CONSTANTS. 



Table {continued). 



243 



The principle of compensation will be however more directly tested by 

 taking the mean speed in ascending each gradient, and the mean speed in de- 

 scending them respectively, and comparing together the means of these se- 

 verally with the mean speed on the levels. This is done in the following 

 table : — 



These results render it quite apparent that the gradients do possess the 

 compensating power ascribed to them. The discrepancy existing among 

 the mean values of the speed, is nothing more than what may be ascribed 

 to casual variations in the moving power. This experiment also was made 

 under very favourable circumstances, the day being quite calm. Without 

 going into the details of the principle on which these remarkable results de- 

 pend, it may be stated generally, that since the chief part of the resistance 

 of a railway train depends on the atmosphere, and is proportional to the 

 square of the velocity, a very small diminution in the velocity itself produces 

 a considerable diminution in its square. A train, in ascending a gradienti 



r2 



