1868. | The Modern Aspects of Physical Science. 339 
assist us to climb, they are but stepping-stones which will be kicked 
away as weadvance. A careful writer, whose work is now before 
us, says he cannot doubt that ere long all physical phenomena will 
be acknowledged to be the results or effects of various, but inter- 
changeable modifications of Energy ; that is, that Motion, Light, 
Heat, and Electricity (and, with many, Life) are but the develop- 
ments of Energy—manifestations of Force. “The term energy 
meaning simply the power of doing work ; force, meaning the power 
of producing energy.” Let us endeavour to give a faithful example 
as an illustration of the meaning of this; for the metaphysical refine- 
ment which involves this hypothesis’ hides it, as by a veil, from 
vulgar intelligences. A mass of gunpowder is a store of force, but 
the force is potential only ; it is placed in a cannon, with a shot— 
an inert mass—in front of it, in the tube. A spark is applied, it 
matters not how, and the force becoming actual, imparts energy to 
the shot, which flies through space and strikes an iron target. The 
primary Energy—shown in motion—is checked, and we find it is 
converted into Heat and Light at the moment the blow is given, 
and, there is but little doubt, also into Electricity. 
The force which was potential in the gunpowder, and which 
was developed, or made actual, by the explosion—producing Motion, 
Heat, Light, and Electricity—is not destroyed; it exists as an 
Eternal Energy, or, in the poetic phrase of a writer of note, the flash 
of the pistol fired by a murderer years long ago is being repeated in 
space, flashing from star to star; and the sigh of the drowning slave 
will undulate for ever, until, at the last day, it becomes the damning 
evidence against the slave-dealer. 
“The principle of the ‘ Conservation of Energy’ implies that when 
once actual energy has been developed in matter, it cannot be anni- 
hilated ; it can only be transferred in some form to other matter. 
So universal is the truth and practical application of this principle 
of conservation, that it may almost be taken as an axiom that it is 
no more the narrowly-bounded power of man to create or annihilate 
force or energy than it is to create matter itself: energy may be 
variously transmuted and directed, and matter may be variously 
combined and modified in form and physical properties, but that is 
all.” — Brooke. 
In passing, it is but justice to state that, although we differ 
widely from Mr. Brooke in many of his conclusions, and fail to see 
the cogency of several of his arguments, we know of no other work 
which more clearly places ‘The Elements of Natural Philosophy ’ 
before the student ; and therefore we recommend it to the attention 
of every one who is desirous of learning the present state of the 
Physical Sciences, and, indeed, of studying the main features of the 
philosophy of the inductive sciences,—except chemistry,—in their 
more important generalities. 
