Juniata sentinel and Republican. [volume] (Mifflintown, Juniata County, Pa.) 1873-1955, 1873-10-29
Scientific.

/ OF THE HoRsE.@Some of our reader!
are finding great difficulty in reconcilinl
the definition of horse power. as giver
by writer's on engineering subjects, will
their own knowledge of the power o
the horse There are three terms which
We must define with precision, before
attempting 10 place the subject before
our readers in such a manner as shat
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 grayitation, of electrical and
magnetic attraction, of heat repulsion
of steam pressure, and of a compressed
spring, are illustrations. II is measured
by the weight which will counterpois'
I it.
Work is force acting through space
and is measured by multiplying the
measure of the force by the measure o.
the space. A force which overcOmes {
resistance of pounds through space
of Z feet, does 81 "foot pounds" o.
work" A weight OF 2 tons Is raised .
feet, or co inches, by the expenditure o.
10 ''foot pounds" or its equivalent, IN
''inch tons"
PO,cer, as the term is only properly
used by engineers, is the amount o.
work done in any given example, IL
some known time. Its unit is called
the "horse power" Thus, machine
doing SO, 900 foot pounds of work in &
minute developes one horse power. The
,,,oabsna in fhn cank
manner, would do $50 pounds of worl
in each second, or 190, 900 foot pound:
during each hour that it might be con
tinuously worked. The horse power
therefore, is a rate of work.
A horse cannot usually exert grea'
power; but the term was first intro
duced by James Watt, and since it,
actual value is a matter of no conse
quence so long as it is well understood
what that value is, engineers have moi
thought it advisable to change it. The
actual power of horses varies immensely
being sometimes more than a horse
power, and often much less. The aver
age power of good draft horse is about
three quarters of a horse power, but il
can only be sustained about eight hours
a day. The same horse drawing in O
gin or mill wonld exert a power which
would average for eight hours work q
trife more than half-horse power. Al
OK is said to have about two thirds the
power of horse, or to be capable oi
exerting about half horse power. The
OK can pull as heavy load as the hor e.
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 a strong draft horse, at about
the same speed. He may therefore be
rated at of .=s of horse power. The
ass rates at about of the power of the
horse, or ! of 3=3-l6 horse power
On a direct pull, the average lift
which horse can exert in steady work
over a single pulley is about 120 pounds
The maximum is probably double thi:
figure. Professor r. H. Thurston, il
the paper on Traction Engines" says
Experiments made by Captain Robert
Merry, at the Jackson Iron Mine, Ne
gaunee, Mich, and the observations
and experiments of the writer, indicate
the maximum direct traction force of &
good horse to be about 80 pounds.
This weight, raised at the rate of 25(
feet per minute or about three mile:
per hour, would give 2J0x250-33, 600
1.9, nearly two horse power for the
power of such an exceptionally strong
animal but We should not expect any
horse to keep up such exertion for more
than very short space of time. The
estimates before given were for average
work, kept up eight hours day fol
days and weeks together.
British engine builders use term, il
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 "dynamometrical horse power,
according as it is determined by the
indicator or the dynamometer. Thus
the engines of the British iron clads,
Devastation and Thunderer, if driven a,
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. In this country, this unfortu.
nate and confusing application of the
term nominal" horse power is al.
most unknown, and We indicate the size
Of an engine by specifying its diameter
of cylinder and length of stroke. The
engines of the Thunderer, for example,
have two cylinders for each of her twin
screws, which are SO inches diameter
and 80 inches stroke.-.Scientifc inner
lean