126 
MINUTES OF PROCEEDINGS OF 
It appears also from these experiments that when the material drawn 
through is the same as that through which it is drawn, the results are much 
more irregular, and the lowest attainable rate, much greater than is the 
case where different materials are used ; the coefficient is also generally 
greater, but this should be considered with reference to its motion in a 
given time to get a true estimate of its value. In the case of gun-metal, 
when drawn through other materials it gave the most uniform results and 
lowest rates—about one inch per minute—but when drawn through gun- 
metal, its motion increased to 30 and 20 inches per minute, and was so 
irregular as to be in one instance only 1J inches per minute. This probably 
arises from cohesion being more readily set up between the surfaces of 
similar, than between those of dissimilar materials. 
It will be seen that there is not much difference in value between the 
coefficients derived from the use of various materials—especially after use, 
as the surfaces appear to rub down to a uniform condition after two or 
three trials. 
Wood through wood:— 
The woods in different combinations, except pine, 
gave a uniformly regular coefficient of . 
Wood through metals :— 
Woods through wrought-iron gave a coefficient of 
„ „ gun-metal ,, „ . 
Metals through woods :— 
Gun-metal, through woods, except teak, gave...... 
Wrought-iron „ „ . 
Metals through metals :— 
Gun-metal, through iron, gave coefficient . 
Iron through gun-metal » « . 
Iron through iron « » .. 
Gun-metal through gun-metal „ . 
For two 
Mean rate, 
inches per 
surfaces. 
minute. 
•350 
30 
•271 
1-6 
•264 
0-9 
•347 
2-8 
•294 
4*0 
•390 
0-33 
•400 
0-33 
•545 
27*0 
•697 
17*0 
Series b. 
TO ASCERTAIN THE EFFECT OF VARYING THE PRESSURE ON THE SAME 
EXTENT OF SURFACE. 
The materials used were the same as in ISeries a, except elm, pine, and 
gun-metal, which were omitted, and ground iron, which was added. 
The bearing surface was in all cases 32 square inches, and the pressure 
varied from 0 # 5 to 2*5 tons. 
The results are given in Tables IX. to XVII. \ Table XVII. being a 
general summary. 
