524 
MESSES. ELEEMING JENKIN AND J. A. EWING ON EEICTION 
wood during the time that the disk was revolving. To test whether this was the case, 
the experiments were in both cases repeated, the supply of unguent being kept up 
continuously during the revolution of the disk. Precisely the same change in ^ was 
observed under these circumstances as under the circumstances in which the experiments 
were at first made. 
As a further confirmation of the result already stated for Case XII., the following 
determinations of [i were made with a new pair of greenheart bearings, but with the 
same steel axle. 
4. For velocity 0-0002 foot per second ^=0-253 
For velocity 0-007 foot per second |W,=0T81 
Greatest velocity observed 0*007 foot per second. 
5. For velocity 0-0002 foot per second ^=0-262 
For velocity 0-0056 foot per second ^=0-203 
Greatest velocity observed 0-0056 foot per second. 
6. For velocity 0-0002 foot per second . ^=0-262 
For velocity 0-008 foot per second //, = 0-207 
Greatest velocity observed 0-0106 foot per second. 
Mean value of p for velocity 0-0002 foot per second .... 0-259 
Mean value of ^ for higher limit of velocity 0-197 
Here the change is equally marked ; the diminution is rather more than twenty per 
cent, of the higher value. It will be observed that although in each set of determinations 
the separate observations agree well, the values obtained from the second set are 
considerably lower than those obtained from the first, no doubt on account of some 
specific difference in the bearing-surfaces. Taking a general mean from the two sets of 
observations, we have 
Value of (Jj for velocity 0-0002 foot per second 0*275 
Value of (Jj for higher limit of velocity 0-217 
Under this set of conditions p appears to undergo little change when the velocity 
exceeds about 0-006 foot per second. 
XIII. Steel on Beech. Dry. 
1. Friction perfectly uniform from velocity 0-0002 foot per 
second to greatest velocity observed, 0*0088 foot per 
second ^=0-366 
2. Friction perfectly uniform from velocity 0-0002 foot per 
second to greatest velocity observed, 0-0089 foot per 
second ^=0*367 
Mean =0-3665 
This result differs from that of Case X. only in the magnitude of the coefficient. 
