of research and the degree of precision attainable. The trustworthiness of the method is shown by the close agreement between its results when applied to the other planets, and the velocities computed from the known astronomical motions of the same bodies.
It is usually thought necessary to caution students of electricity against regarding either of the hypotheses, known respectively as the two-fluid and the one-fluid hypothesis, in the light of an assured thing, and the lecturer commonly hastens to declare that no one knows what electricity is. The declaration is as just as the caution; but it is not in human nature to allow such a declaration long to stand unchallenged. The very fact that it is possibly correct is a stimulus to investigation. Recent research has not conclusively shown what electricity is, but it has considerably shaken the foundations of the above assertion regarding it, and some singular views have been developed that indicate light ahead. We are learning that although the terms "electrification" and "electric" may continue in service to express a condition of matter or to characterize particular phenomena, yet the very name "electricity" may probably become useless and vanish from the vocabulary of physics, for the reason that, instead of electricity being any object, it is probably only a mode in which the ether makes itself manifest. One of the latest views, strongly advocated, is that ether may be analyzed into two constituents, equal and opposite, each endowed with inertia and each connected with the other by elastic ties which are weakened or dissolved by the presence of gross matter. The two constituents are called positive and negative electricity respectively, and of these two electricities the ether is composed. Electric currents which are obtained in such diversity and magnitude for commercial purposes are in almost every case the result of electro-magnetic induction, and are not due to the action of a battery. Yet there is no difference electrically between the currents obtained in the two ways. Maxwell's theory, which treats electro-magnetic action as a variation of ether stress in the medium in which the conductor is situated, may be applied to the conductors of battery currents also, and the medium surrounding the conductor in all cases is the home of the energy transmitted (as we are in the habit of saying) along the wire. But the energy is not transmitted by the wire; on the contrary, the wire, in just so far as it is a good conductor, fails to transmit the energy (the strain) which the action of the generator has sent out into the surrounding medium, and which breaks down or gives way in the conductor. "The energy of a dynamo does not, therefore, travel to a distant motor through the wires, but through the air. The energy of an Atlantic cable does not travel through the wire strands, but through the insulating
