ABRASION OF THE SURFACES OF SOLIDS. 
169 
In an experiment made on one of the corn mills recently erected for His 
Majesty’s victualling department at Deptford, it required to of the weight ol 
the mass to overcome the inertia and friction of the bearings and tangential 
surfaces. In this instance the pressures of the different parts of the machine 
varied from 28lbs. to 8 cwt. per inch area, and the velocities of the surfaces 
from 50 feet to 120 feet per minute. 
REMARKS. — It has been customary to deduct one fourth of the power expended for friction. This 
allowance may maintain in machines newly set in motion. When the bearings have been equalized 
and the rubbing surfaces extended by the abrasion of the irregularities, the friction will be diminished 
and the movements of the machine be more steady. But w'hen the bearings are properly propor- 
tioned to the weight of the parts of a machine, and their surfaces kept from contact by unguents, 
a much less allowance may be made. 
Several experiments were made by giving motion to a fly wheel and a grindstone of known weights 
and revolutions in a given time, and then counting the revolutions after being detached from the 
power ; but owing to the resistance of the air, and the bearings being too small, the results were unsa- 
tisfactory. 
Table XV. Showing the amount of friction (without unguents) of different 
substances, the insistent weight being 36lbs. and within the limits 
of abrasion of the softest substance. 
Steel on ice 
Parts of the 
whole weight. 
Cast iron on wrought iron 
Parts of the 
whole weight. 
. . 5.87 
Ice on ice 
Brass on brass .... 
. . 5.70 
Hard wood on hard wood 
. . 7.73 
Tin on cast iron 
Brass on wrought iron 
. . 7.38 
Tin on wrought iron . 
. . 5.53 
Brass on cast iron 
. . 7.11 
Soft steel on wrought iron 
. . 5.28 
Brass on steel 
Leather on iron 
Soft steel on soft steel . . 
. . 6.85 
Tin on tin 
. . 3.78 
Cast iron on steel 
. . 6.62 
Granite on granite . 
Wrought iron on wrought iron . 
. . 6.26 
Yellow deal on yellow deal 
. . 2.88 
Cast iron on cast iron . . 
. . 6.12 
Sand-stone on sand-stone 
. . 2.75 
Hard brass on cast iron . . . 
. . 6.00 
Woollen cloth on woollen cloth. 
. . 2.30 
These results are collected from the 
different Tables, but 
the 
comparison 
may be made by selecting other values within the limits of abrasion for a mi- 
nimum. 
General Conclusions. 
From what has been stated hitherto it is obvious, — 
1st. That the laws which govern the retardation of bodies gliding over each 
other are as the nature of those bodies. 
MDCCCXXIX. Z 
