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MAGAZINE OF SCIENCE AI?D ART. 
every attempt to bring this great power into practical 
use must prove delusive, or end in disappointment. 
The same argument might have,been urged with equal 
force against the possibility of attaining a speed of GO 
or 70 miles an hour on railways, (which speed has been 
accomplished) because the first locomotive engine tried 
in England on a level made only 5 miles an hour, and 
although ten years later, Stephenson had so little im¬ 
proved the machinery that with 8 carriages and 30 tons 
weight, lie scarcely attained 9 miles an hour. 
11. Scientific men are too often guided in their 
opinions by what has already been “found to answer*' 
and although such may also he the rule of some of the 
wisest mechanics, it is net exactly the way to advance 
our knowledge in any one branch of mechanical science 
or of practical art. ' It is a safe policy, but hateful. 
Our knowledge of cause and effect in physical agents 
is probably yet imperfect, and nothing is more calcu¬ 
lated to limit this knowledge than by giving our blind 
assent to dogmas of doubtful truth, even although they 
may he generally received as true. It should be re¬ 
collected that as evidence of the truth or falsehood of 
some great principle, no experiment is valueless, even 
if unsuccessful, for it is to unsuccessful experiments 
that we owe some of onr most valuable discoveries. 
Thus the failure of an attempt to make a sucking pump 
more than 33 feet long, led to an acquaintance with the 
doctrine of atmospheric pressure, and opened a new 
field of research to the genius of Galileo, Torricelli, 
and Boyle. And Sir Humphrey Davy Is reported on 
an occasion, when ho was shewn a dexterouslv* manipu¬ 
lated experiment, to have exclaimed,. “ I thanlc God 
that I was not made a dexterous manipulator, for the 
most important of my discoveries have been suggested 
to me hy failures. 
12. A "discovery which, after it is known , seems so 
simple that every body wonders that he did not see it, 
may remain hidden for thousands of years, but at last 
prove of sufficient importance to immortalize the name 
of the discoverer. It is equally certain that very few 
discoveries of importance have been made by chance or 
by ignorant persons, but they arc generally made by 
those of competent knowledge who are in search of 
them; and if chance have anything to do with dis¬ 
covery, it is very certain that an individual who is con¬ 
versant with the* laws of matter and of motion, and with 
the construction and use of machinery, has a better 
chance of being a discovoror than a person who is igno¬ 
rant of these matters, and of the applications of the 
science of Dynamics to the production and direction of 
motion. 
13. The science of Dynamics is so well understood 
in the present day, that perhaps few persons are now to 
he found who think that any machine could he con¬ 
structed so as to give a result equal to the motive 
power, and overcome its own friction without a main¬ 
taining Sower; and the time has probably gone by, since 
ingenious persons, reasoning on false data, vainly 
flattered themselves that they might devise some 
machine which should continue in “ perpetual” motion. 
But it does not necessarily follow that it is equally im¬ 
possible to construct an “automatic" engine, or a 
machine which shall contain , the power of motion 
within itself, and which shall give a result equal to the 
motive power abating friction. 
14. The great fundamental principle in the construc¬ 
tion of machinery is that the work done depends in 
quantity only upon the quantity and velocity of the 
motive power, and not upon the form of the machine, 
which has no power to create motive force, but can only 
transmit it, or modify it, to suit particular purposes. 
The nearer, therefore, the effect produced by a machine 
approaches to the power expended in producing it, the 
better and the more perfect is the machine and the 
whole theory of the simple elements of machinery con¬ 
sists in causing the weight which is to be raised to pass 
through a greater or a less space than the power 
which raises it; thus, a weight passing though a certain 
space may be made to raise, through a less space, a 
weight considerably heavier than itself. In every ma¬ 
chine in which power is employed to overcome resist¬ 
ance through the medium of what are termed the me¬ 
chanical “powers,” or more properly the “elements,” 
hv the combination of which all machines are formed; 
although in reality these contrivances are but applica¬ 
tions of the principle of virtual velocities, whereby a 
small force acting through a largo space is converted 
into a great force acting through a small space, yet as 
there is no absolute gain of power, neither is there any 
absolute loss. 
15. Mr. John Smeaton, who was the most talented 
engineer and mechanist of his day, thus defines me¬ 
chanical. power and effect; and his definition is so clear 
and explicit, that it would he difficult to give a better 
one at the present day, although it was written by 
Smeaton nearly 100 years ago. He says:—“The 
word power is used in practical mechanics, I apprehend, 
to signify the exertion of strength, gravitation, impulse, 
or pressure motion, and by means of strength, gravita¬ 
tion, impulse, or pressure Compounded with motion, to 
be capable of producing an effect, and that no effect 
is properly mechanical but what requires such a kind 
of power to produce it.” 
“The raising of a weight relative to the height to 
which It can ho raised, is the most proper measure of 
powor, or in other words, if the weight raised be multi¬ 
plied by the height to which it can be raised in a given 
time, the product is tho measure of the power raising it; 
and consequently all those powers are equal whose pro¬ 
ducts made by such multiplication are equal; for if a 
power can raise twice the weight to the same height in 
the same time that another power can, the first power is 
double the second; and if a power can raise half the 
weight to double the height that another can, those two 
powers are equal.”# 
16. Tho English unit of work is the power necessary 
to raise 1 pound through a space of 1 foot, therefore in 
raising P pounds P feet high, P x F will represent the 
number of units of work consumed, and it is obvious 
that the same number of units of work will be con¬ 
sumed in overcoming a pressure of P pounds through P 
feet, in whatever direction that pressure may act. 
17. Professor Playfair in his “Outlines of Natural 
Philosophy,” Article 86, says, that “Force has, in 
reality, no other signification than d v — d t; and that 
thus an entire Treatise of Dynamics might be written 
in which the word force would not once occur.” Now 
this appears to bo fallacious, for how would it be pos¬ 
sible to leave out of view the conception of force or 
pressure in such a treatise, -which conception is the 
groundwork of the w hole doctrine of mechanics. 
Force is usually and correctly defined as the cause 
which produces or tends to produce motion ; and how¬ 
ever we may define it, it is necessary-that we should 
understand its action distinctly. 
18. The science of dynamics is one in which the 
greatest certainty is attainable by arguments purely 
mathematical; its axioms and laws are few, simple, 
and in tho highest degree distinct and definite. It 
therefore .justly ranks at the head of all the inductive 
sciences, if wo except perhaps astronomy, which holds 
an equal rank, and a portion of which science can only 
be regarded as a branch, of dynamics, for the applica¬ 
tion of dynamics to the motions of the heavenly bodies 
constitutes the science of physical astronomy: and the 
application of dynamics to the calculation, production 
and direction of motion, forms the science of mechanics, 
sometimes called “physical mechanics” in order to 
distinguish it from the general use of the word, which 
comprehends cvexy thing that relates to force and 
motion. 
19. The fundamental principle of the science of 
dynamics, upon which it mainly rests, depends upon a 
property' of the circle, which is that the lengths of 
circles are in proportion to their diameters, or as 3.14159 
to 1. Of however little value or importance this pro- 
* Transactions of the Boyal Society, 1759. 
