366 
Steam Engine. 
U=^9 feet per second, a value which is quite high enough, 
any proposed estimates of the strength of this animal may 
be compared with facility. Thus, for example, let us en- 
quire which is greater, the estimate of Mr. More (men- 
tioned by Mr. Hornblower) of 801bs, three miles per 
hour, or 4| feet per second ; or that of 130lbs. moved at 
the rate of three feet per second ? Here we shall have 
( 9 „ 3 )^ : (9—4*4)^ : : 130 : 7111bs. nearly. 
The operation may easily be performed by means of a 
table of logarithms, and shews that the mean estimate I 
have laid down, when reduced to the same velocity as 
that by Mr. More, furnishes a result less than his by 
Silbs. Which of these is the most accurate can only be 
determined by future experiments. 
If, however, either of these estimates should be adopt- 
ed, it may be proper to remark that they would not hold 
with regard to the power of horses working in circular 
paths ; yet, if it be at all proper to use horse-poxvers in 
estimating the energy of machines, it seems most natural 
to take these powers as exerted by the animal in a round 
walk ; so that it is still necessary to have a series of ex- 
periments to determine the values of w, and the relation of 
M and V when horses draw in circular walks of different 
radii. I say, of different radii, because it is certain that 
£ceteris paribus^ the greater the radius of the circle in 
whose circumference the animal moves, the less fatigue 
will be occasioned by that kind of motion. Indeed it is 
obvious, that since a rectilinear motion is the most easy 
and natural for the horse, the less the line in which he 
moves is curved, with the greater facility he will walk 
over it, and the less he need recline from the vertical po- 
sition. Besides this, wdth equal velocity at the circum- 
ference, the centrifugal force will be less in the greater 
circle, which will proportionally diminish the friction of 
the cylindrical part of the trunnions, and the labour of 
