PROFESSOR OSBORNE REYNOLDS ON ROLLING-FRICTION. 
167 
two plates together with powdered Turkey-stone. In this way the plates were made so 
true that the roller would remain in [any position, and would roll either way with an 
inclination of 1 in 5000, or about 1 foot in a mile. It appeared impossible, however, 
to produce surfaces altogether free from inequalities, which may be seen from the 
results of the experiments. 
The effect of Oiling the Surface. 
In the first experiments the surface on which the roller was to roll was brought into 
a level position, so that the roller when placed on it remained at rest. A line of sights, 
consisting of a mark on the glass and a pin-hole in a plate fixed at some distance, was 
then brought to bear on a mark on the top of the roller, so that the least motion could 
be detected, and the position of the roller could be recovered after it had been allowed 
to roll in one direction. The level was then adjusted to read zero on the staff, and the 
table tipped until the roller rolled off in one direction. The reading of the level was 
then noted, and the same operation repeated in the opposite direction, the roller having- 
in the mean time been brought back into its former position. Sundry observations were 
then taken with different points of the plane and roller in contact. After a considerable 
number of observations had thus been taken oil was poured into the glass until the 
roller was covered, and then the observations were repeated. Table I. shows a series of 
Table I. — Cast-iron Roller on Plate-glass. (The distance of the Staff from the Object- 
glass of the Level =50 feet. The Divisions on the Scale = yq-q foot.) 
Clean. 
Oiled. 
Headings. 
Headings. 
Difference. 
Difference. 
To. 
From. 
To. 
From. 
-5-0 
1-2 
6-2 
-5-0 
3-2 
8-2 
o 
-2-3 
3-5 
5-8 
-3-3 
2 - 5 
5-8 
—2-6 
2-0 
4-6 
-4-0 
2-0 
6-0 
o 
—4-5 
1-4 
5-9 
-4-1 
1-0 
5-1 
-4-7 
2-0 
6-7 
-1-8 
4-0 
5-8 
■B 
-2-8 
3-5 
6-3 
-3-0 
2-0 
5-0 
J 
-3-2 
4-5 
7-7 
-5-8 
0-5 
6-3 
-4-0 
3-4 
7-4 
—5-2 
0-3 
5-5 
Mean 
..6-3 
Mean 
.. 5-9 
-2-6 
-0-7 
1-9 
-3-0 
-0-4 
2-6 
'■Z 
-3-5 
-1-5 
2-0 
-1-8 
+ 1-0 
2-8 
o 
-3-5 
-2-0 
1-5 
— 2-5 
o-o 
2-5 
O ^ 
-4-2 
—2-2 
2-0 
2-5 
+ 0-2 
2-7 
■"> s 
-1*5 
+ 0-6 
2-1 
-3-9 
—1-0 
2-9 
-2-5 
-0-5 
2-0 
-3-0 
-0-8 
2-2 
o g 
.—1-9 
0-0 
1-9 
-4-4 
—2-0 
2-4 
% 
-0-7 
+ 1-5 
2-1 
-1-0 
+ 1-5 
2-5 
3 
Mean 
..1-9 
Mean 
.. 2-6 
