MAGAZINE Off SCIENCE AND ART. 
191 
friction and surface resistance, that great natural op- 
poser to motion; but a simple method of employing 
the power of the horse, in such a manner that a maxi¬ 
mum effect may be obtained from his weight and mus¬ 
cular force combined , and at the same time a speed 
compatible with the exigencies of passenger traffic, is 
still a desideratum in engineering science, and this 
desideratum it is the object of the horse locomotive and 
power engine to supply. 
We have in the horse a moving power capable of 
changing its force momentarily, and of overcoming 
almost any inclination that may occur on a railway ; 
hut as it has been ascertained that the resistance from 
friction on railways docs not increase with an increase 
of speed, it follows that much advantage might be ob¬ 
tained by an increase of velocity greatly exceeding that, 
at which a horse could exert any force of traction by 
ordinary draught on the road. 
Mr. Wood, in his Treatise on Railroads, states that 
“ we may reckon a horse’s muscular exertion divided 
into eight parts, seven of which are required to urge his 
own weight forward, and one that of the load,” 
Now this statement, without any reference to the 
horse’s speed, is manifestly incorrect, for in estimating 
the effect of animal strength in ordinary traction, one 
law is very obvious, which is, that as the load is in¬ 
creased (all other things being the same) the speed of 
the animal must be diminished ; and on the other hand, 
as the velocity is increased, so the load must be 
diminished. 
There are evidently two extreme cases of animal 
exertion, for there is a certain speed at which a horse 
can, draw or carry no appreciable load, and, on the 
other hand, there is some load so great that the animal 
cannot movent. In both these extreme cases the useful 
effect is “nil,” for wluit is termed the useful effect 
depends on two things, viz., the load which is carried, 
and the speed with which it is carried. It is in fact 
estimated hv multiplying the load by the velocity. 
It is usually estimated that the greatest unloaded 
speed of ahorse in miles per hour is represented by 15, 
aud the mean power of the draught horso is calculated 
hy Mr. Leslie’s formula as follows:—(15 — 0)2==lbs. 
avoirdupois for the traction of a strong horse; and 
(12—0)2=rlbs. for the traction of an ordinary horse, 0 
being the velocity in miles per hour. 
These formula: must, however, be regarded as ap¬ 
proximative only, as the expression must not be con¬ 
sidered as constant, but obviously varies much accord¬ 
ing to the breed and training of the animal. 
Adopting, however, the first formula, and assuming 
the horse’s speed at 3 miles an hour, 144 lbs. would 
then represent the tractive force of the horse, and this < 
very nearly approximates with Air. Watts’ estimate of t 
horse-power, viz. 150 lbs., when moving at the rate cf < 
2} miles an hour ; and a horse of ordinary strength ■ 
will draw at this rate for eight hours a-day, which is 
equivalent to a distance of twenty miles, Tho number 
of units of work assigned by Wait to a horse is there¬ 
fore 33,000 lbs. raised 1 foot high in a minute, but some 
engineers estimate it a little lower. 
It follows, therefore, that a horse would draw on a 
level railway at a speed of 21 miles an hour, a gross 
load of 16g tons, estimating the resistance at 9 lbs. per 
ton. But if we increase his speed to 5 miles an hour, 
we reduce his tractive force, according to Mr. Leslie, 
from 144 to 100 lbs.; and at a speed of 10 miles an 
hour, his tractive force is reduced to 25 lbs. only, • 
equivalent to the traction of less than 3 tons. Beyond 
this speed, a horse has little or no tractive force left, 
aifd has consequently no power of drawing a load, ex¬ 
cept it be a very light one. 
In order to investigate the power which is expended ; 
ly a horse when drawing heavy weights on a common j 
road, it is necessary to revert to some of tho first prin- < 
ciples of active strength or animal energy. The force j 
obtained through this wedinm must evidently vary i 
according to different individuals, both as regards their i 
weight and their muscular force, and the" dexterity ^ 
acquired by habit. 
A horse put into harness, and ihaking an effort to 
draw a load, bends his body forwards, inclines his legs, 
aud throws that part of his weight into the collar which 
is required to overcome tho resistance of the load, and 
this so much the more as the load is the more consider¬ 
able; so that when a horse is employed in drawing 
heavy weights, his effort will depend both upon his'own 
weight and his muscular force. 
It is, therefore, an error to suppose that a horse’s 
weight is disadvantageous to him in drawing heavy 
loads at a slow speed, for the reverse is the case, as he 
opposes hie weight to ‘the weight of the load ; and 
indeed it might be useful in some cases to load the 
back of a draught horse to a small extent: for although 
at first sight it might be thought to augment unneces- 
‘ f sarily his fatigue, yet it must be recollected that tho 
weight with which a horse is charged vertically is 
added in part to the effort which he makes in the direc¬ 
tion of traction, and thus dispense;-, with the necessity 
of his inclining so much forward as ho must otherwise 
do. Carters are generally well aware of this, and are 
careful to dispose of tho load in snch a manner that tho 
shaft shall throw a due proportion of the weight on the 
hack of tho shaft horse. 
_ The absolute or dead weight of a horse which is con¬ 
sidered bv Air. Wood to be so disadvantageous to him, 
and to absorb so much of his power, varies considerably 
indifferent animals. A largo and powerful draught 
horse will weigh nearly 10 cwt., or 1120 lbs., aud an 
active light horse about 8 cwt., or S9G lbs. The mean 
of these, or 1008 lbs., may therefore be assumed as tho 
weight of an ordinary horse. 
Dr. Olinthus Gregory, in the first volume of his Ale- 
chanirs, estimates the strength of a horse as being 
equivalent to 420 lbs. at a dead pull, and for a short 
period only; and whoever has witnessed the effort of a 
London brewer’s dray-horse in drawing casks out of a 
cellar, must be aware that this requires a very great, 
although only a momentary effort. 
Considering the horse as a machine, it is obviously 
desirous to obtain the greatest possible amount of useful 
effect from it, with the least wear and tear, and this is 
the great object of the horse-locomotive and power- 
engine. 
The weight of the horse is of no disadvantage what¬ 
ever to him in tho horse locomotive, but directly the 
reverse ; and so far from relieving him of any part of 
his weight, it is proposed to add to it by loading him 
until a certain weight. 
On a railway worked by the horse-locomotive, the 
compensating effect of gradients comes into full opera¬ 
tion, as upon those parts of the line where tho descent 
exceeds 1 in 250, or 21 feet in a mile, the resistance-in 
descending would be nothing since the load would move 
down by its unassisted gravity, aud the horso would bo 
carried down the incline by the load. 
The doctrine of compensating gradients has been pro¬ 
nounced paradoxical with regard'to a railway worked* 
Ly locomotive engines ; but it is not so with a railway 
worked by horse-locomotives, as a variation of speed in 
the train would be the whole amount of inconvenience 
that could ensue, and this inconvenience could easily 
be obviated. 
The horses being carried down by the load where the 
gradient exceeds 1 in 250, the only effort he would have 
to make would be to lift his feet clear of the revolving 
platform, and the horse being supported by a strong 
girth, can neither stumble nor fall. 
On referring to the account of the experiments made 
in 1830,_ on the Liverpool and .Manchester Railway, 
with various kinds of locomotive engines, we find one 
constructed by Air. Brandreth, and called the “Cyclo- 
pedc.” This machine consisted of a carriage carrying 
a horizontal platform, supported on rollers, and carried 
over a drum at each end. The horse was yoked to the 
frame, and by treading on the horizontal platform, ho 
moved it round, and, through the medium of spur 
wheels, the motion was communicated to the driving 
wheels. 
The trial made with this machine was, however, un- 
