128 
MINUTES OF PROCEEDINGS OF 
Series e. 
This series was undertaken with the view of obtaining coefficients which 
would more strictly compare with one another than do those in the foregoing 
experiments, where the conditions influencing the results were found to be 
not identical, more especially— 
The effect of continued use. 
The variation of rate of motion. 
With respect to the 1st, the experiments were conducted so as to give the 
coefficients for each pressure under the same conditions of use; thus in the 
1st trial the pieces were passed through under a \ ton pressure (the lightest 
pressure) and were not again used under this pressure until the 10 th trial. 
In the 2nd trial they were subjected to a pressure of 2| tons (the heaviest 
pressure), which was repeated in the 9th trial, and so on with the other 
pressures; the mean coefficients arrived at in the summary being the means 
of the two series at the same pressure. 
With regard to the second influence referred to, the rates were varied 
under each pressure; the results given in the tables being in all cases the 
means of several. By this method a tolerable uniformity is arrived at in 
the rates at different pressures; and a juster comparison may be made 
between them. 
The materials used were wrouglit-iron, ground and surfaced, gun metal, 
also ground and surfaced, and teak. 
Erom this series it appears that the resistance of friction increases as the 
surface becomes condensed with use; that varying the pressure has no 
effect on the coefficient, and that when the rate is uniform there is little 
difference in the value of the coefficients of the materials tried. 
The following are the mean coefficients at the lowest and highest common 
rates, viz. 3 ins. and 20 ins. per minute (two sliding surfaces):— 
Common rates. 
Lowest=3". Highest=20". 
Teak through surfaced iron . *369 *552. 
Ground gun-metal, through ground iron. *416 *471. 
Surfaced „ surfaced n . ’429 ’514. 
Ground iron through ground iron . *402 *502. 
The following are the mean coefficients at the lowest and highest common 
rates, viz. 0*25 ins. and 30 ins. per minute, omitting ground iron through 
ground iron, which was incapable of giving the lowest rate :— 
Common rates. 
Lowest= 5 " Highest=30" 
Teak through surfaced iron . *270 ‘655 
Ground gun-metal through ground iron . *352 *525 
Surfaced „ surfaced u . *346 *637 
The results are given in Tables XXXIY. to XXXVIII. 
The mean values of the coefficients of each material at various rates of 
