107 
Information respecting Rail-Roads. 
divided by the number of times the diameter of the wheel con- 
tains that of the axle, will express the whole resistance, when the 
machinery is in tolerably good order. This, when the ordinary 
wheels, three feet in diameter, are used, amounts to about 11 \ lb. 
per ton ; so that, if the constant progressive effort of any power 
be known, we can readily tell with how much it ought to be load- 
ed on a rail-road. 
There is a very great variety of opinion and statement with 
respect to the power of horses at different velocities. The ex- 
periments do not yet seem to be sufficient in number, and suf- 
ficiently varied, to afford unquestionable conclusions. The for- 
mula (12 — v) 2 seems to give the velocity corresponding to the 
maximum effect, a higher value than experience warrants. The 
Tables given by Mr Wood, of the performance of horses on 
the colliery railways, represent the effect of the horse as so very 
irregular, that they lead to no very satisfactory conclusions ; 
because r we do not know what effect such irregularities may 
have, in influencing the amount of the work done. His state- 
ment, that the power of a horse travelling 20 miles per day, at 
the rate of 2 miles per hour, may be represented by 112 lb. is 
more probably under the truth than above it. Mr Tredgold 
has pointed out, that the general formula ought to include in 
it as an element, the length of time during which the labour 
is continued ; and that, corresponding to each assumed dura- 
tion, there is a velocity which produces a maximum of effect, 
and that this velocity must have a certain relation to that rate 
of motion which a horse can sustain unloaded, during the num- 
ber of hours assumed for the duration of his labour. But the 
assumptions from which are deduced the numerical values of 
those velocities, are either unintelligible to me, or are totally 
inadmissible. There results from them the strange position, 
that the muscular force which can be continued for a day, has 
to the weight of the animal the ratio of 3.37 : 1, though in fact 
the true ratio is more nearly the inverse of this. If, according 
to Mr Tredgold’s estimate, a horse could exert a constant force 
of 125 lb. during 6 hours, at the rate of 3 miles per hour, his 
day’s work on a rail-road would, at the rate of 11 § lb. per ton, 
be 10.8 tons conveyed 18 miles : according to Mr Wood’s esti- 
mate, it would be 6.6 tons conveyed 20 miles. In these esti- 
