52 
Report of the Judges on the 
Oxford in 1870 ; and lastly, in tlieir Report on the traction en- 
gines tried at Wolverhampton in 1871, have had to comment 
on the attempt, or on the absence of an attempt, by the Society, 
to settle that most difficult question, What shall be deemed a 
"horse-power " — not the theoretical horse-power, but the commer- 
cial horse-power. The theoretical horse-power, as all engineers 
and all readers of the ' Journal ' of the Society know, is 33,000 
lbs. raised 1 foot high in a minute, or the equivalent of this, 
i. e. such a number of pounds as will give, when multiplied by the 
feet moved through, the sum of 33,000 as the result. It is not the 
settlement of this horse-power, then, which has occupied the Society 
from time to time, but the settlement of how , many such theo- 
retical horse-powers an engine shall be capable of developing 
for one commercial or nominal horse-power ; in other words, 
the difficulty is to determine, what size of engine shall be given 
to a purchaser for a nominal horse-power. Upon this question of 
size will depend, whether, when an engine, say a 10-horse, is put 
to work, it Avill give to its users 20, 30, 40, or even 50 theoretical 
horse-power for the commercial or nominal lO-horse-power. 
With respect to horse-power, the purchasing public behave 
towards engine-makers in, we were about to say, a very Jack 
Cade sort of spirit ; but we feel that this would be unjust 
towards Jack Cade. That enlightened representative of the people 
merely required that " seven halfpenny loaves should be sold 
for a penny, and that the three-hooped pot should have ten 
hoops " (or about 3 ' to 1), while the purchasing public will not 
be content unless the 8-horse engine will work up to 30-horse, 
and they like as much more as they can get. 
At Bury, the Society determined that engines with single 
cylinders should have a piston area of 10 circular inches for 
each horse-power, so that a 9 -inch cylinder, giving 81 circular 
inches of area, was taken as 8yV-borse-power. But if the 
engines had two cylinders, as many had in those days, then, for 
some never explained reason, in fact for an inscrutable reason 
(if that which is inscrutable can be a reason), their aggregate 
area, in circular inches, was to be divided by 9, as with two 
cylinders that number of circular inches was to be deemed to be 
sufficient for a horse-power. 
At Oxford, the Society left the Exhibitor to give any measure 
he pleased, so long as he did not exceed IS'li circular inches 
in piston area, per horse-power, for the 4-horse engines ; and 13'22 
circular inches per horse-power, for the 10-liorse engines. 
It will be seen that these Oxford rules were about from 30 to 
nearly 50 per cent, in excess of the Bury rule ; according as the 
10, or the 9, circular inches there prescribed, be used as the 
standard of comparison. 
