the Pendulum- Accelerometer. 



265 



This reasoning obviously extends to partial removal of the 



jrake, and is in fact general. 



Fi»". 5. 



In order to facilitate the accurate setting up of the 

 instrument, it is fitted with a transverse level to ensure getting 

 the knife-edges approximately level, the pendulum itself 

 being relied on to obtain the correct zero position, a separate 

 pencil or datum-line marker being fitted to the instrument, 

 and the setting being correct when the datum-line and record- 

 line correspond when the car is at rest on the level. When 

 setting up on a motor-car, an approximately level place is 

 found on the road, two trials of the setting are made with the 

 car in opposite positions and the error divided. When on 

 the railway a known level is chosen for setting up. 



A few typical diagrams taken on the railway and on motor- 

 cars are given in figs. 6, 7, and 8. 



In fig. 8 we have a group of brake diagrams taken on the 

 original model in 1889 on the Great Western and the 

 Metropolitan Railways. These at once bring out a point of 

 great interest, the sudden change of acceleration that takes 

 place at the exact instant the train comes to rest ; this is a 

 characteristic of nearly all brake diagrams and will be referred 

 to again. The max. negative acceleration recorded in these 

 diagrams is about 4 ft./sec. sec. A starting diagram taken on 

 the same journey is given. The maximum starting acceleration 

 here recorded is about '6. There is unfortunately no record 

 of the type or weight of engine or the number or weight of 

 the coaches. 



