528 
ON FRICTION BETWEEN SURFACES MOVING AT LOW SPEEDS. 
corresponding to the lowest velocity to which the observations extended. Columns V. 
and VI. show the change in the value of [/, wherever any was observed, Column V. 
giving the changed value of jW«, and Column VI. the velocity at which the change 
appeared to be sensibly complete. Columns V. and VI. are left blank wherever no 
change was detected in the value of p from the least velocity up to the greatest velocity 
observed, which is given in Column VII. 
Table II. 
I. 
II. 
III. 
IV. 
V. 
VI. 
VII. 
Greatest 
VIII. 
p at velo- 
At velo- 
velocity to 
Number. 
Surfaces. 
Condition. 
city 0-0002 
p changes to 
city (ft. 
which ob- 
servation 
extends 
Remarks. 
ft. per sec. 
per sec.). 
(ft. per sec.). 
I. 
Steel on Steel. 
Dry. 
0-351 
0-0089 
II. 
„ „ 
Oiled. 
0-118 
(?) 0-129 
0-005 
0-0065 
f Condition of surfaces 
III. 
„ „ 
Wet with water. 
0-208 
0-0058 
-j rapidly changing, so 
[ as to increase p. 
IV. 
Steel on Brass. 
Dry. 
0-195 
0-0059 
Very irregular. 
V. 
„ ,, 
Oiled. 
0-146 
0-0064 
VI. 
» « 
Wet with water. 
0-105 
0-0048 
f Condition of surfaces 
VII. 
Steel on Agate. 
Dry. 
0-200 
0-0064 
-J rapidly changing, so 
VIII. 
» » 
Oiled. 
0-107 
0-0054 
(_ as to increase p. 
IX. 
Wet with water. 
0-166 
(?) 0-146 
0-006 
0-0069 
X. 
Steel on Greenheart. 
Dry. 
0-215 
0-0064 
XI. 
” 
” 
Oiled. 
0-124 
0-077 
0-096 
0-062 
0-005 
0-004 
0-0064 
0-0055 
f After prolonged ex- 
\ posure to oil. 
XII. 
Wet with water. 
0-275 
0-217 
0-006 
0-0106 
XIII. 
Steel on Beech. 
Dry. 
0-366 
0 0089 
XIV. 
„ „ 
Oiled. 
0-126 
0-101 
0-005 
0-0057 
f Change in p still 
XV. 
” 
Wet with water. 
0-356 
0-279 
0-008 
0-0080 
l going on at greatest 
[ velocity observed. 
