196 report — 1877. 



First, by the length of the interval of time which occurs between the moment 

 of performing the operation which has the effect of putting the brake into action, 

 and the moment wheu the brake-blocks begin to place an effective grip upon the 

 wheels, and 



Secondly, by the amount of pressure brought to bear on each wheel, and by the 

 constancy or otherwise of the action after the blocks have come to grip the wheels. 



It would not appear to be a difficult task to arrange the proportions of the parts 

 of the mechanism of any brake in such wise as to ensure that an assigned and 

 definite pressure shall be brought to bear on each block ; and it is doubtless from 

 the want of such suitable adjustment that the pressure in some of the examples of 

 continuous brakes is found to be too feeble for accomplishing a rapid stop. 



The reduction of the interval of time elapsing before the pressure is fairly put 

 on may not so easily be effected, being in a measure incidental, more or less, to each 

 specific form of brake. 



That much room for improvement remained in the way of effecting an equal 

 and constant pressure on the wheels throughout the period of the brake-action was 

 evident from the results brought out by au analysis of the time-records. 



These have been translated into the form of the submitted diagram (Plato IV.), 

 from which it will be observed that the retarding force, in its earlier stage, instead of 

 being uniform and constant, is broken up into a series of impulses more or less violent, 

 but becoming more uniform towards the close of the period of its action, a condi- 

 tion due probably to the increasing number of the wheels which had become skidded. 



The diagram serves to illustrate this effect. It has been prepared from the 

 electrically recorded time-observations. 



The ordinates represent by scale the mean speeds at successive intervals of space 

 traversed. 



The curved lines connecting the extremities of the ordinates thus show approxi- 

 mately the variations of the retarding force. 



It is this intermittent fitful action which produces undue strains on the drawbars 

 and chains, and the unpleasant sensation frequently experienced during quick stops. 



It would seem that after the brakes are first brought to bite the wheels, their 

 hold becomes relaxed, a slip takes place, followed by successive bites and slips, the 

 latter giving rise to sudden accelerations of speed. 



The action of a perfect brake should exactly resemble that which gravity would 

 cause if an ascending incline of uniform gradient could be suddenly presented in 

 front of the train to stop its motion. 



Under such conditions no inconvenience or danger is to be apprehended from 

 accomplishing the stop in even shorter distances than any effected during the course 

 of our experiments. 



Practically no inconvenience was experienced in stopping one of the best 

 appointed trains, 200 tons in weight, running at over 50 miles an hour, in a period 

 of 18 seconds ; and generally the stops were effected without unpleasant sensation, 

 though in some instances the recoil of the buffers at the final moment of stoppage 

 gave rise to a sensible and disagreeable jerk. 



It became obvious, during the course of our experiments, that a valuable addition 

 of brake-power, under the immediate control of the driver, was afforded by the 

 fitting of breaks to the engines ; and it is satisfactory to find that the recommenda- 

 tion of the Royal Commissioners in this respect has met with the prompt attention 

 of Railway Companies. 



"We learn from the Board of Trade return already referred to, that about 250 

 engines have been so fitted, about 100 engines with the Westinghouse, 100 with 

 Smith's Vacuum, 30 with Stroudley's Steam Brake, and the rest with the brakes of 

 Saunders, Barker, and the Steel-M c Irmes, showing how fully the importance of 

 utilizing the heavy weight of the engine is becoming appreciated, and affording 

 proof at the same time that the apprehensions of injury to the engines entertained 

 by some of the locomotive superintendents are virtually without foundation. 



It is believed that far less objection attaches to the application of brakes to thi$ 

 engine-wheels than to the act of reversing by back steam, whilst such reversing waij 

 proved by our experiments to be less effective than brakes. 



