518 



EEPOET — 1879. 



applied to every wheel of the train. The shaded area below CD shows the extra 

 retardation consumed to overcome the momentum of the braked wheels. 



The diagonal line AE shows the stop with the same retardation applied to half 

 the wheels and half the weight of the train, as indicated by the line FG. The 

 shaded portion below the line FG shows the extra retardation caused in overcoming 

 the momentum of the braked wheels, and the shade below AE shows the extra 

 distance run by the train owing to the momentum of the unbraked wheels. 



The diagonal AH shows the stop with the same retardation of -20 applied to 

 ^-wheels and ^-weight of train as indicated by JK. The thickness of line JK 

 and diagonal area shaded below AH show respectively the extra retardation con- 

 sumed in overcoming the momentum of the braked wheels, and the extra distance 

 run by the train in consequence of the momentum of the unbraked wheels. 



From the experiments it was found that the best results were obtained in cases 

 where the pressure applied at first was from about If to twice the weight on the 

 wheels, and where the reduction of the pressure was effected with sufficient 

 rapidity towards the end of the stop to prevent the friction increasing at a sufficient 

 rate to skid the wheels. 



The necessity for the instantaneous application of the maximum brake-block 

 pressure throughout the train is evident from the fact that, at a speed which is 

 frequently obtained, namely, sixty miles per hour, a train passes over 88 feet each 

 second ; therefore the loss of two or three seconds in applying the brakes means 

 often the difference between safety and danger, and the rapidity of a stop largely 

 depends upon the rapidity with which all the brake-blocks can be brought to act 

 against the wheels of a train. 



This points to the advantage of being able to move the brake-blocks with great 

 rapidity from their position of inaction to that of contact with the wheels ; because 

 it is essential to provide that the brake-blocks, when out of use, shall be removed 

 to a distance from the wheels sufficient to prevent the possibility of their dragging 

 against the wheels, and thus retard the progress of the train. The question of the 

 rapidity with which brakes can be applied in practice is thus one of much 

 importance. 



Some experiments were made in October 1878, upon the North Eastern 

 Railway, on a train fitted with the vacuum brake, and one fitted with the Westing- 

 house brake, to ascertain the time which was required after moving the brake- 

 handle to set the brakes with various degrees of force in different parts of the train. 

 The following table shows the result arrived at : — 



A long interval of time between brakes coming on at the front and rear of a 

 train may become a source of danger ; and improvements have been introduced in 

 both the vacuum and Westinghouse apparatus since that date to reduce the interval 

 as shown by the experiments. 



In the Westinghouse brake a simplified triple valve has been adopted, the 

 friction has been reduced by the use of an enlarged pipe and by the removal of 

 bends in the connections between the carriages ; by these alterations the interval 

 of time required to put on the brakes, as shown in the above table, has since been 

 reduced by nearly one-half, and an experiment recently made on the application of 

 the brake in rear of a train of twenty-four vehicles on the Western Railway of 



