CH. X AXLE FRICTION 1 59 



to Morin, of from 0.05 to 0.065. Later experi- 

 ments with machine shafting bring this to a lower 

 figure, but for coach axles 0.065 * s a ^ air value. 

 This friction is much diminished by thorough oil- 

 ing, and with a constant supply, or bath, of oil it is 

 sometimes not over 0.005, or one-tenth of the value 

 given above. When the bearing is thus flooded 

 with oil, the surfaces do not touch each other at all, 

 and the friction is that of a fluid. 



This condition cannot be fully maintained in a 

 wheel, but the distribution of the oil by means of 

 shallow grooves in the axle-arm, or in the box, and 

 a large supply of oil in the wheel-cap, approach 

 it and form an important feature of the Collinge 

 axle. Heating the oil, even to a moderate de- 

 gree, increases the friction, and great heating, as 

 we all know, by the expansion of the arm, soon 

 brings the wheel to a stop. 



As is now well exemplified in the bicycle, the 

 ball-bearing, by converting the sliding axle friction 

 into rolling friction between very hard and smooth 

 surfaces, diminishes greatly the resistance to the 

 turning of the wheel. The rolline friction between 

 perfectly spherical, highly polished, hard, steel balls 

 and a hard, steel surface is so small that it may be 

 said to be nothing. In the bicycle, this has been 

 successfully turned to account, and there is no 

 reason why the ball-bearing should not be adopted 

 in a coach wheel, except for the comparative com- 

 plication of such arrangements, and from the fact 



