l6o BALL-BEARINGS CH. X 



that the horse, to whom the draught is of prime 

 consequence, is not able to express his opinion as 

 readily as the human cyclist. Some forms of car- 

 riage axles with ball-bearings have been already 

 brought out but are not yet in general use. 



The results of some late experiments, made at 

 the Engineering Department of Yorkshire College, 

 Leeds {Engineering, Sept. 11, 1896), are interesting 

 as showing" the resistance to crushing of hard steel 

 balls. Balls of a quarter-inch diameter stood a 

 pressure of five tons each, before crushing ; those 

 of a half-inch, more than ten tons. These were 

 statical pressures ; the balls would not probably 

 stand so much if they were in rolling motion. 



Taking 0.063 as the coefficient of friction, r the 

 radius of the axle, and R that of the wheel, or of 

 the average of the front and hind wheels, the ex- 

 pression 0.065 p w ^ represent the proportion of 



the weight of the coach without its wheels, which 

 measures the axle friction. It is of course the 

 weight of the coach resting on the axles, that 

 causes the friction on the axles. If, therefore, a 

 coach with its load, and without its wheels, weighs 

 3100 pounds, has axles two inches in diameter, and 

 wheels averaging 46 inches in diameter, the expres- 

 sion will be/" R (W — w) t * or 0.065 -£$ 3100 = 8.77 

 pounds, as the amount of the axle friction, and 

 since experiment gives an average of 70 pounds 



* W being the weight of the whole coach and w that of the wheels. 



