But what, then, is this strange power that has produced all these multifarious results? It would be hard to propound a scientific query that has been more variously answered. Ever since the first primitive man observed the strange effect produced by rubbing a piece of amber, thoughtful minds must have striven to explain that effect. Ever since the eighteenth-century scientist began his more elaborate studies of electricity, theories in abundance have been propounded. And yet we are not quite sure that even the science of to-day can give a correct answer as to the nature of electricity. At the very least, however, it is able to give some interesting suggestions which seem to show that we are in a fair way to solve this world-old mystery. And, curiously enough, the very newest explanations are not so very far away from some eighteenth-century theories which for a long time were looked at askance if not altogether discarded. In particular, the theory of Benjamin Franklin, which considered electricity as an immaterial fluid bearing certain curious relations to tangible matter, is found to serve singularly well as an aid to the interpretation of the very newest experiments. FRANKLIN'S ONE-FLUID THEORY Such being the case, we must consider this theory of Franklin's somewhat in detail. Perhaps we cannot do better than state the theory in the words of the celebrated physicist, Dr. Thomas Young, as given in his work on natural philosophy, published in 1807. By quoting from this old work we shall make sure that we are not reading any modern interpretations into the theory. "It is supposed," says Young, "that a peculiar ethereal fluid pervades the pores, if not the actual substance of the earth and of all other material bodies, passing through them with more or less facility, according to their different powers of conducting it; that particles of this fluid repel each other, and are attracted by particles of common matter; that particles of common matter also repel each other; and that these attractions and repulsions are equal among themselves, and vary inversely as to squares of the distances of the particles. The effects of this fluid are distinguished from those of all other substances by an attractive or repulsive quality, which it appears to communicate to different bodies, and which differs in general from other attractions and repulsions by its immediate diminution or cessation when the bodies, acting on each other, come into contact, or are touched by other bodies.... In general, a body is said to be electrified when it contains, either as a whole or in any of its parts, more or less of the electric fluid than is natural to it.... In this common neutral state of all bodies, the electrical fluid, which is everywhere present, is so distributed that the various forces hold each other exactly in equilibrium and the separate results are destroyed, unless we choose to consider gravitation itself as arising from a comparatively slight inequality