512 



REPORT — 1879. 



f to p in diagram 4, with a speed of eleven miles per hour, is much larger than 

 that of F to p in diagram 5, with a speed of fifty-five miles per hour. 



N°5. 



1 ' I ' I ' i * I ' I ' I ' I ' I ' I ■' ' ' I ' I ' ' ■ !"• I ' I • I ' I ' I I I — | i | ' I I I' I ■ | ' I i | 

 Seamdso 12 343618910 11 1213 -U IS 1617 13 13 20 21 22 23 21 2S2& 27 28 2339 



The following table shows the coefficient of friction obtained from these ex- 

 periments at vai'ying speeds between cast-iron brake-blocks and steel tyres : — 



If the position of the brake-blocks were always the same at the same speed, 

 some simple rule might be deduced which would give the pressure required at 

 each speed for obtaining a certain amount of retardation ; but when the speed of 

 the van was kept nearly uniform by the effort of the engine, the friction of the 

 blocks decreased ; and this occurred, notwithstanding a continued increase of the 



