Electricity is the same now as it has ever been, yet it was once spoken of as a fluid, then as a force, now as an energy readily convertible into caloric or mechanical energy; and in what light it will be considered fifty years hence no one can predict.
Now, what I desire to enforce here is, that amid all these changes and revolutions of theories, so called, it is simply man, the interpreter, that has erred, and not Nature; her laws are the same; we simply have not been able to read them correctly, and perhaps never will be.
What, it may be asked, are we to do, then? Must we cease theorizing;? Not at all. The lesson to be learned from this is to be more modest in our generalizations; to generalize as far as our carefully-made-out facts will permit us, and no further; check the imagination, and let it not run riot and shipwreck us upon some metaphysical quicksand.
The fact is, it becomes a question whether there is such a thing as pure theory in science. No true scientific theory deserves the name that is not based on verified hypothesis; in fact, it is but a concise interpretation of the deductions of scientific facts. Dumas has well said that theories are like crutches, the strength of them is, to be tested by attempting to walk with them. And I might further add, that very often scientists, who are without sure-footed facts to carry them along, take to these crutches.
It is common to speak of the theory of gravitation, when there is nothing purely hypothetical in connection with the manner in which it was studied; in it we only see a clear generalization of observed laws which govern the mutual attraction of bodies. If at any time Newton did assume an hypothesis, it was only for the purpose of facilitating his calculations: "Newton's passage from the falling of an apple to the falling of a moon was at the outset a leap of the imagination;" but it was this hypothesis, verified by mathematics, which gave to the so-called theory of gravitation its present status.
In regard to light, we are in the habit of connecting with it a pure hypothesis, viz., the impressions of light being produced by emission from luminous bodies, or by the undulation of an all-pervading, attenuated medium; and these hypotheses are to be regarded as probable so long as the phenomena of light are explained by them, and no longer. The failure to explain one single well-observed fact is sufficient to cast doubt upon or subvert any pure hypothesis, as has been the case with the emission theory of light, and may be the fate of the undulatory theory, which, however, up to the present time, serves in all cases.
It is not my object to criticise the speculations of any one or more of the modern scientists who have carried their investigations into the world of the imagination; in fact, it could not be done in a discourse so limited as this, and one only intended as a prologue to the
