522 MESSES. ELEEMING JERKIN AND J. A. EWING ON EKICTION 
VIII. Steel on Polished Agate. Oiled. 
1. Friction uniform from velocity 0-0002 foot per second 
to greatest velocity observed, 0-0054 foot per second . ^/,=0T06 
2. Friction uniform from velocity 0-0002 foot per second 
to greatest velocity observed, 0-0041 foot per second . ^=0-107 
3. Friction uniform from velocity 0-0002 foot per second 
to greatest velocity observed, 0-0054 foot per second . ^=0-107 
Mean #<=0*107 
IX. Steel on Polished Agate. Wet with water. 
The determinations here are not perfectly definite, but appear to agree in showing 
that the friction increases slightly at very low velocities. 
Taking the mean of three observations, we have 
For velocity 0-0002 foot per second ^=0*166 
For velocity 0-0060 foot per second ^=0-146 
The greatest velocity observed was 0-0069 foot per second, and it is doubtful whether 
gj was not still sensibly diminishing at that velocity. 
X. Steel on Greenheart. Dry. 
1. Friction uniform from velocity 0-0002 foot per second to 
greatest velocity observed, 0-0058 foot per second . . ^=0-212 
2. Friction uniform from velocity 0-0002 foot per second to 
greatest velocity observed, 0-0047 foot per second . . ^=0*213 
3. Friction uniform from velocity 0-0002 foot per second to 
greatest velocity observed, 0-0064 foot per second . . j a-=0 , 221 
Mean ^=0*215 
XI. Steel on Greenheart. Oiled. 
In this case there was a very marked increase of friction as the velocity diminished. 
From a velocity of 0-0002 to about 0-005 foot per second, the friction gradually dimi- 
nished, and at the latter velocity it appeared to have become nearly constant. 
1. For velocity 0-0002 foot per second ^=0-123 
For velocity 0-005 foot per second ^-0-094 
Greatest velocity observed 0*0064 foot per second. 
2. For velocity 0*0002 foot per second ^=0-126 
For velocity 0-004 foot per second ^=0-098 
Greatest velocity observed 0-0042 foot per second. 
3. For velocity 0-0002 foot per second ^=0-124 
For velocity 0-005 foot per second ^=0*097 
Greatest velocity observed 0-0050 foot per second. 
