The Pendulum Accelerometer 



261 



tractive effort on the whole vehicle can be ascertained if that 

 acting on any portion of its mass be measured. 



It is evident that the actual measurement on a known mass 

 carried on the vehicle could be made by means of a spring- 

 balance, the mass being mounted so as to permit of its hori- 

 zontal motion only ; but it is also possible and it is easier to 

 arrive at the same result by arranging the mass as the bob of 

 a pendulum and reading the coefficient of traction directly in 

 the tangent of the angle of its deflexion. 



It will be recognized at once that the quantity being 

 measured in this manner is the acceleration of the vehicle : 

 hence the instrument is in reality an accelerometer, the 

 measurement of gross tractive efforts and resistances requiring 

 in many instances the instrument to be used indirectly, the 

 direct reading giving the net difference between the pro- 

 pelling and resisting forces. 



The first pendulum accelerometer was made by the writer 

 as far back as 1889 ; this somewhat rough model is still in 

 existence (fig. 1) , and many of the diagrams taken on the 



Fiff. 2. 



railway in 1889 have been preserved (fig. 9). This instru- 

 ment was not fitted with clockwork, so that the time-scale is 

 irregular. 



Fig. 2 shows in diagram form the essential working parts 



