510 



EEPORT — 1879. 



upon the rail. The experiments were made with the object of measuring the force 

 thus brought into action. 



The first result of the experiment was to show conclusively that the retarding 

 effect of a wheel sliding upon a rail is much less than when braked with such a 

 force as would just allow it to continue to revolve. 



The annexed copies of two sets of diagrams (No. 1 and No. 2) taken during 

 the experiments, show, more clearly than can be explained, the difference in the 

 retarding force, before the wheels begin to slide upon the rails, and after. These 



yv° 2. 



NOej 

 perTwar 



* 9 ~"s\ ^Ea-penment IP? 18, 



\ I °"~p ~^ Slip Stop with Skidding 

 (rmdieruL level 



ttu 



ran 



z\ 



two experiments were made with a single van slipped from the engine, the brakes 

 going on automatically when separation from the engine took place, s is a line 

 showing the speed of the van at each instant, the scale for which is at the left side. 

 p is the pressure against four blocks acting upon one pair of wheels ; the vertical 

 height of p by the scale on the right hand, multiplied by 240, gives the total pres- 

 sure in pounds on the four blocks. F is the line showing the retarding effect of 

 the four blocks upon the one pair of wheels before the wheels began to slide upon 

 the rails, and/ shows the effect while the wheels were sliding upon the rails. The 



/x... 



fC3 



/ £acpervnentJf? 19^*'^. P 

 S ^*\ Gnadient rising ] in 264 \ 



ts 



Iks 



'20. 



HC 

 SO 

 6C 

 70. 

 SO. 



sc 



r 



Speed of Vaji p' 



%~X—x — x—x — x—x — x—x — x— x-*-*. 



i y i ' " < > * ■ i 



75 



^ T v r» y '" T - 



vertical height of f or/, according to scale b, multiplied by 60, gives the retarda- 

 tion in pounds. It will be seen that the stop was made in half the time with the 

 wheels braked but not skidded of that required when the wheels were skidded. 



The accompanying diagram 3 shows in another way the comparative retarding 

 effect of the brakes when acting on the revolving wheels, and when applied with 

 sufficient force to skid the wheels. 



An experiment was made by keeping the van at a uniform speed on a rising 



