170 
PROFESSOR OSBORNE REYNOLDS ON ROLLING-FRICTION. 
position it was placed. By blackleading the surface this tendency was considerably 
reduced, although not altogether destroyed. These oscillations could not have been 
caused by the mere resistance which the one surface offered to the sliding of the other 
over it, unless also this resistance threw the surfaces into constraint from which they 
are constantly endeavouring to free themselves. 
The effect of the Softness of the Materials. 
Having found that oil did not reduce the resistance, the experiments were continued 
with a view to ascertain how far the softness of the material had any thing to do with 
it. As materials of several degrees of softness had already been tried, the only question 
was to settle how far the difference in the results observed was due to their softness 
and how far it might be due to some other difference in their nature. To show this 
cast iron and brass were tried, which are of much the same hardness as glass, and yet 
of an altogether different nature in other respects, the surface of the glass being 
highly polished, while that of the metal was dull as it had been left by the grinding. 
The results of these experiments are contained in Tables IV. and V. 
Table IY. — Cast-iron Boiler on Brass. 
Clean. 
Oiled. 
Readings. 
Readings. 
Difference. 
Difference. 
To. 
From. 
To. 
From. 
-13-2 
— 5-5 
7-7 
-2-0 
4-3-8 
5-8 
-g 
— 5-5 
+ 2-0 
7-5 
—4-5 
+ 1-2 
5-7 
S 
- 3-2 
+ 5-0 
8-2 
-2-8 
4-3-8 
6-6 
3 
— 3-5 
+ 4-5 
8-0 
-2-9 
4-5-2 
8-1 
4h 
- 3-5 
4-3-8 
7-3 
-1-7 
4-5-8 
7-5 
-2 
- 7-0 
4- 1-5 
8-5 
-5-0 
4-1-0 
60 
S 
- 5-0 
4-2-2 
7-2 
-3-0 
+ 3*5 
6-5 
GO 
- 4-6 
4-3-0 
7-6 
-3-0 
+ 2*9 
5-9 
Mean 
. . 7 75 
Mean 
-2-4 
-0-8 
1-6 
-1-5 
4-1-0 
2-5 
'■Z 
-2-4 
-0-4 
2-0 
0-0 
+ 1-8 
1-8 
I 
-1-8 
+ 0-7 
2-5 
-1-2 
4-1-6 
2-8 
§ ■ 
— 2-0 
-0-4 
1-6 
—2-0 
4-0-6 
2-6 
% .§ 
— 2-8 
-1-0 
1-8 
-2-3 
4-0-5 
2-8 
r±4 ~0 
-2-5 
4-0-2 
2-7 
—2-0 
+ 1-0 
3-0 
J s 
— 0-2 
+ 2-0 
2-2 
-1-2 
4-1-5 
2-7 
2'2 1 
0-0 
2-2 
—0-9 
4-1-6 
2-5 
P3 
Mean 
. . 2-07 
1 
Mean 
. . 2-58 
The means of the results for all the materials are contained in Table VI. Comparing 
these we see at once the effect of softness : the cast iron, brass, and glass are very nearly 
the same, and the slight difference is not greater than may be accounted for by a slight 
