FRICTION. 
77 a 
upon rollers, that ate laid between them and 
the ground, with ease and safety, when it 
would be almost impossible to move them 
otherwise. 
The form and disposition of friction-wheels 
is represented by tig. 94, Plate Miscel. which 
exhibits a front view of the axis of a large 
wheel, which moves between the friction-, 
wheels A, B, 0. Here the end of the axis 
(and the same thing must be understood of 
the opposite extremity of the axis) instead of 
moving in a hole, moves between the cir- 
cumferences of three wheels, each or which 
is moveable upon its own axis, and is uncon- 
nected with the others. Now if the end of 
the axis turned in a hole, the surface of the 
hole would stand still, and the surface of the 
axis would rub against it; whereas, when the 
axis moves between the circumferences of 
the wheels A, B, C, its surface does not rub 
against, but is successively applied to the 
circumferences of those wheels ; so that this 
sort of motion lias the same advantage over 
the turning of the axis in a hole, that the 
moving of a heavy body upon rollers has 
over the simple method of dragging it upon 
the ground. In this construction the contact 
of the axis moves the wheels A, B, C, 
round their axis, where indeed some friction 
must unavoidably take place, but that friction 
is very trifling ; for if the circumference of 
the axis be to that of each wheel as 1 to 20, 
the axis must make 20 revolutions whilst the 
friction-wheels will turn round once only. 
A few years ago the same principle was 
applied in a very ingenious manner, by Mr. J. 
Garnett, then of Bristol, to pulleys, and other 
sorts of circular motion round an axis, lor 
which he obtained a patent. Tiie use of this 
application has proved very advantageous, 
especially on board of ships, where it has 
been found, that with a set of Mr. Garnett’s 
pulleys, three men were able to draw as 
much weight as live men were barely able 
to accomplish with a similar set of common 
pulleys. 
One of these pulleys is represented by fig. 
95, Plate Miscel. where the shaded part B B B 
is the pulley, A is the axis, round which 
are the cylindrical rollers, which are situated 
between the axis and the inside cavity of the 
pulley. The ends of the axis A are fixed in 
a block, after the usual manner. Every one 
of the rollers has an axis, the extremities of 
which turn in holes made in two brass or iron 
flat rings. 
After having given a general explanation 
of the action of rollers, the advantage which 
Mr. Garnett’s pulleys must have over those 
of the common sort, needs no farther illus- 
tration. We shall, however, only observe, that 
the friction of the pivots of each roller in the 
holes of the brass rings is very inconsiderable; 
for those holes are made rather large, the use 
of the axes to the rollers being only to pre- 
vent their running one against the other. 
Nor does the addition of weight upon the 
pulley increase that friction, for the addition 
■of weight. upon the pulley will press the rol- 
lers harder upon the axis A, but not upon 
their own axes, as may be easily understood 
bv inspecting the figure. 
Fb.ic.ti ox maybe considered chemically 
as a source of caloric. Fires are often kindled 
by rubbing pieces of dry wood smartly against 
one another. It is well known that heavy 
loaded carts sometimes take lire by the fric- 
tion between the axle-tree and the wheel. 
Now in what manner is the caloric evolved 
or accumulated by friction? Not bv increas- 
ing the density ot the bodies rubbed against 
each other, as happens in cases of percus- 
sion, for heat is produced by rubbing soft 
bodies against each other, the density of 
which therefore cannot be increased by that 
means, as any one may convince himself by 
rubbing bis hand smartly against his coat. It 
is true, indeed, that heat is not produced by j 
the friction of liquids; but then they are too , 
yielding to be subjected to strong friction, j 
it is not owing to the specific caloric of the 
rubbed bodies decreasing; for Count Bum- I 
ford found that there was no sensible de- | 
crease, nor, if there was a decrease, would 
it be sufficient to account for the vast quan- 
tity of heat which is sometimes produced by 
friction. 
Count "Rum ford took a cannon Cast solid 
and rough, as it came from the foundery ; he 
caused its extremity to be cutoff", and form- 
ed, in that part, a solid cylinder attached to 
the cannon inches in diameter, and 9-?— 
inches long. It remained joined to the rest 
of the metal by a small cylindrical neck. In 
this cylinder a hole was bored 3.7 inches in 
diameter and 7.2 inches in length. Into this 
hole was put a burnt steel borer, which by 
means of horses was made to rub against its 
bottom; at the same time a small hole was 
made in the cylinder perpendicular to the 
bore, and ending in the solid part a little be- 
yond tiie end of the bore, 'this was for in- 
troducing a th rmometer to measure the heat 
of the cylinder. The cylinder was wrapt 
round with flannel to keep in the heat. The 
borer pressed against the bottom ot the hole 
with a force equal to about 10,000lbs. avoir- 
dupois, and the cylinder was turned round at 
the rate of 32 times in a minute. At the be- 
ginning of the experiment tiie temperature 
of the cylinder was 60°; at the end of 30 mi- 
nutes, when it had made 960 revolutions, its 
temperature was 130°. The quantity ot me- 
tallic dust or scales produced by this friction 
amounted to 837 grains. Now if we were to 
suppose that ail the caloric was evolved from 
these scales, as they amounted to just 
part of the cylinder, they must Have given 
out 948° to raise the Cylinder 1°, and -conse- 
quently 66300° to raise it 70° or to 130°, 
w hich is certainly incredible. 
Neither is the caloric evolved during fric- 
tion, owing to the combinatiofi of oxygen 
with the bodies themselves, or any part of 
them. By means of a piece of clock-work, 
Mr. Pictet made small cups (fixed on the 
axis of one of the wheels), to move round 
with considerable rapidity, and he made 
various substances rub against the out- 
sides of these cups, while the bulb of a very 
delicate thermometer placed within them 
marked the heat produced. The whole ma- 
chine was of* a size sufficiently small to be in- 
troduced into the receiver of an air-pump. 
By means of this machine a piece of adaman- 
tine spar was made to rub against a steel cup 
in air: Sparks were produced in great abun- 
dance during the whole time, but the ther- 
mometer did not rise. The same experi- 
ment was repeated in the exhausted receiver 
of an air-pump (the manometer standing at 
four lines); no sparks were produced, but a 
kind of phosphoric light was visible in the 
dark. The thermometer did not rise. A 
piece of brass, being made to rub in tiie same 
manner against a much smaller brass cup in 
air, tae thermometer (which almost filled die 
cup) rose 0.3°, but did not begin to rise till 
the friction' was over. This shews us that 
the motion produced in the air carried off 
the caloric as it was ev Ived. In the ex- 
hausted receiver it began to rise ihe moment 
the friction began, and rose in all 1.2°. When 
a bit o; wood was made io rub against the 
brass cup in the aii, the thermometer rose 
0.7°, and on substituting also a wooden cup, 
it rose 2 i°, and in the exhausted receiver 2.4°, 
and in air condensed to 1^ atmospheres it 
rose 0.5°. 
If these experiments should not be thought 
conclusive, there are others, winch will not 
leave a doubt that the heat produced by fric- 
tion is not connected with the decomposition 
of oxygen gas. Co. nt Romford contrived, 
until his usual ingenuity, to inclose the cylin- 
der above described m a wooden box liiied 
with wate , which effectually excluded all 
air, as the cylinder itself and the borer were 
surrounded with water, and at the same time 
did not impede the motion otthe instrument. 
The quantity of water amounted to 18.77 lbs. 
avoirdupois, and at the beginning of the 
experiment was at the temperature of 60°. 
Aker the cylinder had revolved for an hour 
at the rate of 32 times in a minute, the tem- 
perature of the water was 107°; in 30 mi- 
nutes more it was 178°; and in two hours 
and 30 minutes after the experiment began, 
the water actually boiled. According to the 
computation of count Rumtbrd, the caloric 
produced would have been sufficient to heat 
26.58 lbs. avoirdupois of ice-cold w ater boil- 
ing hot; and it would have required n ne wax 
candles of a moderate size, burning with a 
clear liame all the time the experiment last- 
ed, to have produced as much heat. In this 
experiment all access or water into the hole 
in the cylinder where the friction took place 
was prevented. But in another experiment, 
the result of w hich was precisely the same, 
the water was allowed free access. 
Tlje caloric then, which appears in conse- 
quence of friction, is neither produced by an 
increase of the density, nor by an alteration 
in the specific caloric of the substances ex- 
posed to friction, nor is it owing to the de- 
composition of the oxygen of the atmosphere. 
Whence then is it derived? "I his question 
cannot at present be answered: but this is no 
reason for concluding with count Rumford, 
that there is no such substance as caloric at 
all, but that it is merely a peculiar kind of 
motion; because other facts demonstrate the 
existence of caloric as a substance. Was it 
possible to prove that the accumulation of 
caloric by friction is incompatible with its 
being a substance, in that case count Bum- 
ford’s conclusion would be a fair one; but 
this surely has not been done. We are cer- 
tainly not yet sufficiently acquainted with 
the laws of the motion of caloric, to be able 
to affirm with certainty that friction cannot 
cause it to accumulate in the bodies rubbed. 
This we know at least to be the case with 
electricity. Nobody has been hitherto able 
to demonstrate in what manner it is accumu- 
lated by friction ; and yet this has not been. 
