POWER OF A HORSE IN DRAWING. 
613 
rale : — Given the velocity, or rate per hour, 
at which a man travels, to find his power 
or force of traction : — Square the difference 
hetioeen 6 miles and the given velocity in 
miles, multiply by 2, and the product will 
be the required force in pounds avoirdupois. 
This rule gives the following results ; — 
Velocities, 0 1 2 3 4 5 6 
Forces, 72 50 32 18 8 2 0 
From this rule, it appears that the great- 
est useful effect is produced, when a man 
walks at the rate of 2 miles an hour, his 
power of traction being then 32 lbs ; this 
amounts to a force of 3,379,200 lbs., raised 
1 foot per day of 10 hours — an estimate 
which is only about 1-16 part less than that 
assumed by Dr. T. Young. 
9. In other kinds of human labour, such 
as climbing stairs, ladders, and mountains, 
loaded or unloaded ; pumping water, sawing 
wood and stones, driving piles, working at 
a capstan or windlass, wheeling loaded 
barrows, digging with a spade, turning a 
winch, &c., it is almost impossible to esta- 
blish any proper means of comparison, or to 
reduce the calculations of the forces em- 
ployed in each kind of labour to a common 
or fixed rule. For farther illustration of 
this subject, therefore, we must refer to the 
authors already cited, and to such well- 
known writers as Desaguliers, Emerson, 
Coulomb, and Hachette. See Gregory’s 
Mechanics, arts, 66 — 69. 
1 0. Horse Power.'] The absolute force 
of the horse, in drawing horizontally, as as- 
certained by the dynamometer, is on an 
average no less than 770 lbs. ; consequently 
the power of a horse in this kind of mo- 
mentary exertion, is equal to the force of 7 
men. The amount of the permanent force 
of a horse, however, is found to be con- 
siderably less than this, varying from that of 
6 men to that of 5 men according to differ- 
ent estimates. Dr. O. Gregory reckons the 
power of a horse equivalent to that of 6 
men ; but he states this power as equivalent 
only to 420 lbs. at a dead pull. Desaguliers, 
Smeaton, and Leslie, reckon the power of a 
horse equivalent, on an average, to that of 
5 men. Tredgold reckons a horse power 
equal to that of 6 men, at a medium, and 
the rate of travelling about the same as, or 
perhaps rather less than, that of a man, 
when continued for 8 hours.* On the whole, 
it appears, when the period of continuance 
is made an element in the calculation, that 
the power of a horse, working 8 hours 
a-day, is, on an average, not more than 
equivalent to that of five men, working 10 
hours a-day. 
♦ Notes to Buchanan on Mill Work, vol. 
i. p. 167. 
11. Permanent force of a Horse.] Desa- 
guliers reckons that a horse will walk at the 
rate of 2§ miles per hour, against a resist- 
ance of 200 lbs., that is, at the rate of 220 
feet per minute ; a horse’s power is there- 
fore equivalent to a force that will raise 
44,000 lbs. 1 foot per minute, when working 
8 hours per day. Mr. Watt found, from 
repeated experiments, that a horse treading 
a mill path at the rate of 2f miles an hour, 
will, on an average, raise about 150 lbs. by 
a cord hanging over a pulley, which is 
equivalent to raising 33,000 lbs., 1 foot 
high in a minute. His steam-engines were 
calculated to work at the rate of 44,000 lbs. 
per horse power; but he allowed only 33,000 
lbs. in his calculations, considering the 
difference due to loss by friction. Boulton 
and Watt ultimately estimated the horse 
power at 32,000 lbs. Tredgold reckons 
it at 27,500 lbs. when continued 8 hours 
a-day, and 33,000 lbs. when continued 6 
hours a-day. Smeaton estimated a horse 
power at 22,916 lbs ; this is generally con- 
sidered too low, otherwise the loss by fric- 
tion must have been very considerable. It 
is coipmon in practice, to reckon that it re- 
quires one horse’s power to drive 100 spin- 
dles with preparation of cotton water 
twist; 1000 spindles with preparation cotton 
mule yarn ; and 75 spindles with prepara- 
tion flax yarn. See Buchanan on Mill 
Work, p. 157. 
12. Leslie has elegantly simplified Euler’s 
formula, as applied to the power of a horse 
in drawing ;* and we may now express it 
also in the words of the following rule : — 
Given the velocity or rateper hour at which 
a horse travels to find his power of trac- 
tion: — Square the difference between 12 
miles and the given velocity in miles, the re- 
sult will be the required power in pounds 
avoirdupois. From this rule we obtain the 
following results : — 
Velocities, 0 l 2 3 4 .7 6 7 8 9 10 11 12 
borces, 144 121 I 0 O 8 I 64 49 36 25 10 9 4 1 0 
Thus it appears that the greatest useful 
effect is produced when a horse walks at the 
rate of 4 miles an hour, his power of trac- 
tion being then 64 lbs. ; this amounts to a 
force of 22,528 lbs., raised 1 foot high per 
minute — an estimate which agrees very 
nearly with that of Smeaton. 
13. The power of a horse depending 
greatly on his speed, formulae have been 
given for the calculation of this element, 
according to its duration. The following 
rule is derived from Leslie’s formula: — 
Divide the square of the difference between 
20 hours and the given duration of a horse's 
motion in hours by 25, and the quotient 
will be his maximum velocity in miles per 
Natural Philosophy, p. 283 . 
