168 
PROFESSOR OSBORNE REYNOLDS ON ROLLING-FRICTION. 
such observations for a surface of plate-glass both with and without oil. In these 
particular experiments, however, the surface was simply oiled, it having been found by 
experience that the effect was the same as when the glass was filled with oil. It will 
be seen that in these experiments the advantage is slightly in favour of the oiled glass. 
The results contained in the second part of this Table were obtained by starting the 
roller in one direction against the inclination of the plane with just sufficient velocity to 
carry it up to a certain point, the inclination of the plane being adjusted until it would 
roll back. In this way the advantage is against the oil. This, however, I think is due 
to the surface-tension or fluid-friction arising from the motion of the roller. 
There is a very marked difference between these inclinations and those required to 
start the roller from rest, a difference which appears to exist with all the materials 
tried, and which I think is only in part explained by the roughness of the surface. 
In these experiments with a surface of glass the friction was so small that the 
inequalities of the surface rendered the results very irregular and uncertain. To obviate 
this a surface of box-wood cut across the grain was next tried. This, being softer, 
allowed the roller to indent it more than the glass and gave rise to greater friction, and 
hence the inequalities in the surface are less apparent in the results, which are shown 
in Table II. These observations were made in the same way as those with the glass, 
except that blacMead was substituted for oil. The effect of the blacklead seems to 
Table II. — Cast-iron Holler on Box-wood. 
Clean. 
Blackleaded. 
Readings. 
Difference. 
Readings. 
Difference. 
To. 
Erom. 
To. 
Erom. 
- 3-0 
+ 
5-0 
8-0 
-4-8 
+ 6-0 
10-8 
m 
- 3-0 
+ 
8-0 
11-0 
-3-2 
+ 7-8 
ll-o 
fn 
- 4-0 
+ 
5-8 
9-8 
-7-6 
+ 2-4 
10-0 
a 
p 
- 4-0 
+ 
6-0 
10-0 
-0-5 
+ 8-0 
8-5 
-10-0 
0-0 
10-0 
+ 0-8 
4-10-0 
9-2 
+ 3-4 
+ 12-8 
9-4 ' 
+ 1-0 
+ 8-9 
7-9 
ci 
- 4-0 
+ 
7-0 
11-0 
-9-0 
- 1-2 
7-8 
Zfl 
- 3-2 
+ 
8-0 
11-2 
-9-8 
- 1-0 
8-8 
Mean 
. 10-05 
Mean 
.. 9-25 
+ 7-0 
+ 12-2 
5-2 
—1-0 
+ 1-0 
3-5 
-4-3 
— 5-0 
+ 
0-4 
5-4 
—1-2 
+ 1-2 
4-0 
OQ 
-2-0 
+ 
4-2 
6-2 
0-0 
+2-0 
2-0 
d 
<D ^ 
-2-1 
+ 
3-8 
5-9 
+2-0 
+ 5-0 
3-0 
% .2 
+ 3-2 
+ 
9-0 
5-8 
+ 1-2 
+ 4-0 
2-8 
r*4 2 
+ 1-3 
-f 
7-0 
5-7 
+3-0 
+ 6-2 
3-2 
§ d 
-2-0 
+ 
4-0 
6-0 
-6-4 
-3-0 
3-6 
-Q 
-2-6 
4- 
2-9 
5-5 
-7-6 
-3*0 
4-6 
o 
P3 
Mean. 
.. 5-71 
Mean 
.. 3-34 
