CHAP. VII I. 



EXPERIMENTS ON FRICTION. 



135 



OLD K11X1N 



)RTH LOCOMOTIVE, STILL IX USE 



Vivian had intended their first engine. But the accuracy 

 with which he estimated the resistance to which loads were 

 exposed on railways, arising from friction and gravity, 

 led him at a very early stage to reject the idea of ever 

 applying steam power economically to common road 

 travelling. In October. 1818, he made a series off 

 careful experiments in conjunction with Mr. Nicholas! 

 Wood, on the resistance to which carriages were ex- 

 posed on railways, testing the results by means of a 

 dynamometer of his own construction. The series of 

 practical observations made by means of this instru- 

 ment were interesting, as the first systematic attempt 

 to determine the precise amount of resistance to car- 

 riages moving along railways. It was then for the 

 first time ascertained by experiment that the friction 

 was a constant quantity at all velocities. Although 

 this theory had long before been developed by Yince 

 and Coulomb, and was well known to scientific men as an 

 established truth, yet at the time when Mr. Stephenson 

 made his experiments, the deductions of philosophers 



