American citizen. [volume] (Canton, Miss.) 1864-1890, 1873-06-28
The Horse Power and the Power Of
the Horse.

SOME of our readers are finding great
difficulty in reconciling the definition of
horse power, as given by writers on en-
gineering subjects, with their own knowl-
edge of the power of the horse. There
are three terms which we must define with
precision, before attempting to place the
subject before our readers in such a man
ner as shall give them an accurate notion
of the meaning of the term first referred
to.
Force is defined to be anything which
produces or tends to produce motion, or
change Of motion, in bodies. The force
of graduation, of electrical and magnetic
attraction, of heat repulsion, of steam
pressure, and of IA compressed spring, are
illustrations. 1t is measured by the weight
which will coun.erpoise it.
Work is force acting through space, and
is measured by multiplying the measure
of the force by the measure of the space.
A force which overcomes resistance of 5
pounds through space of Z feet, does 30
'foot pounds of work" A weight of
2 tons is raised 5 feet, or 60 inches, by the
expenditure of 10 "foot pounds" or its
equivalent, 100 Inch TONS"
POtcer, as the term is only properly used
by engineers, is the amount of work done
in any given example, in some known
time. Its unit is called the ''horse
power Thus, machine doing 5000
foot pounds of work in a minute devef
opes one horse power. The same ma
chine, working in the same manner, would
do $50 pounds of work in each second, or
10000 foot pounds during each hour that
it might be continuously worked. The
horse power, therefore, is Il rate of work.
a horse cannot usually exert great
power; but the term was first introduced
by James Watt, and since its actual value
is a matter of no consequence so long as
it is well understood what that value is,
| engineers have not thought it advisable to
| change it. The actual power of horses
varies immensely, being sometimes more
than horse power, and often much less.
The average power of a good draft horse
is about three quarters of a horse power,
but it can only be sustained about eight
hours day. The same horse drawing in
| IA gin or a mill would exert power which
would average for eight hours work trif1e
| more than half horse power. An OK is
said to have about two thirds the power
of a horse, or TO be capable of exerting
about half horse power The OK can
pull as heavy load as the horse, but
moves more slowly, and hence does less
work in a given time, and rates less horse
power
The mule pulls about one half the load
of strong draft horse, at about the same
speed. He may therefore be rated at Is
of 4-ss of a horse power. The ass rates
at about a of the power of the horse, or
Il of 34-3-16 horse power.
On direct pull, the average lift which
a horse can exert in steady work over a
single pulley is about 100 pounds. The
maximum is probably double this figure.
Professor r. II. Thurston, in the paper on
Traction Engines of which we gave an
abstract some months ago, says: expert
ments made by Captain Robert Merry, at
the jackson Iron Mine, Negaunee, Mich,
and the observations and experiments of
the writer, indicate the maximum direct
traction force of good horse to be about
$50 pounds This weight, raised at the
rate of $50 feet per minute or about three
miles per hour. would give 250x25O- 3333
OO0-1.9, nearly two horse power for the
power of such an exceptionally strong ami
NAL; but we should not expect any horse
to keep up such eXertiOn for more than a
| very short space of time. The estimates
before given were for average work, kept
up eight hours day for days and weeks
! together
| British engine builders use a term, in
giving the size of steam engines, which is
| known as nominal horse power and is
| much smaller than the actual power of
| the engine, which is usually known as the
indicated horse power" or the dynamo
| mctrical horse power" according as it is
| determined by the indicator or The dyna-
mometer Thus the engines of the British
iron clads, Devastation and TlnInderer, if
driven at the low speed and with the low
steam used in the time of James Watt,
would be of about 500 horse power They
| still are said to be of 800 nominal horse
power, but the Thunderer, in her recent
trial, developed 800 indicated horse pow
er. In this country, this unfortunate and
confusing application of the term nom
inal' horse power is almost unknown,
and we indicate the size of an engine by