44G Report on the Trials of Implements at Oxford. 
Jously deep coal-pit, so that a rope could be let down the pit, the rope having 
a given weight at the end of it, and could be wound up round a pulley in a 
given time. Then one should be able to say, such a weight has been raised 
through such a distance in a minute of time, and that represents so many 
horse-power. But as deep coal-pits are luxuries not to be found in the neigh- 
bourhood of all trial-yards, it becomes necessary to devise an apparatus which 
shall have the same elfect in putting work upon the engine as if it were lifting 
a weight, but without ever lifting a weight at all. That which is called a 
" Friction Break" is an apparatus of this description. 
As an elementary illustration of the principles and construction of a 
" Friction Break," imagine a smooth wheel inside a smooth ring (a break-ring), 
capable of being tightened, round about which ring was wound a rope with the 
required weight at the end of it. If on turning this wheel, say by an engine, 
the brealt-band were tightened sufficiently, it is clear it could notwithstanding 
the weight be made to revolve with the wheel. It would then wind up the 
rope and draw up the weight, just as we have supposed might be done by 
drawing tlie weight up the coal-pit ; on the other hand, the band might be 
left so slack, that notwithstanding the wheel continues to revolve, the weight 
might as a sailor would say, overhaul the band and cause it to turn in the 
direction opposite to that of the wheel, and thus let the weight run down. 
But assume that the band could be slackened to just such an extent that it 
■would neither run round with the wheel, to wind up the weight, nor allow it 
to descend contrary to the action of the wheel, then it is clear that although 
the band and the weight would remain stationary, the friction put by that 
band upon the wheel revolving within it must be precisely the same as if the 
wheel were really winding the weight ; because, although it is not winding it, 
it is holding it up, and thus it is in fact subjected to the whole weight. It is 
upon this principle that the breaks used by the (Society are constructed. They 
have in addition to that which has been stated in this mere elementary 
description, an arrangement of levers invented by the late Mr. Appold, .of 
such a nature that if the weight fall a little it immediately tightens the break, 
and if it rise a little it immediately slackens it. 
Now, being provided with such an imi^lement as this, one is able, by causing 
the wheel within the break to be turned round by the engine to be tried, to 
put upon that engine just such an amount of resistance as it is intended to 
overcome. Thus, if an engine be a 10-horse engine, it should lift 330,000 lbs. 
one foot high in a minute ; or, if the break were running at the rate of 2000 
feet per minute, it should lift, or, what is the same thing, uphold suspended 
165 lbs. If this be done, then the engine is really delivering to the break 
10-horse-powcr ; and if, instead of working this useless break, it were work- 
ing a thrashing-machine or a corn-mill, it would imder similar circumstances 
do work equal to ten-horses'-power. The break being thus adjusted, the 
next thing is to find what is the amount of coals that will be consumed to 
drive tlie engine during a given time. It might be thought that nothing was 
more easy than to give out a certain weight of coals, to allow them to be put 
upon the fire and burnt, to note the time during which they were burning, and 
then say that such a weight of coals worked the engine for so many hours, and 
that the weight of coals divided by the horse-power, multiplied into the 
number of hours would give the coal consumed per hour per horse ; but a 
little reflection will show that this apparently simple and fair proceeding 
would not be a true test. The water in the boiler would be cold, the boiler 
itself would be cold, and a large amount of fuel would be consumed in the 
mere getting-up of steam, which would be a loss that would tell most seriously 
upon a short trial. To obviate these sources of error the Society pursues the 
following course : — There is issued to each exhibitor sufficient wood and coals 
to get up steam, and to run his engine for a short time, at the stiijulated pace. 
