A man of science has presented to the Paris Academy of Sciences a paper in which he attempts to prove from the results of certain experiments that the atoms of magnetic bodies, such as iron and manganese, contain definite quantities of an elementary magnetic _substance_, which he proposes to call "magneton." This is regarded as a sequel to the new way of regarding electricity; for in the electrons we now seem to find a means of defining electricity in terms of a unit of substance. Electricity, light, and other physical forces, have at different times been defined either as kinds of matter or as modes of motion. At the present moment, many people think, we are passing from the kinetic to the corpuscular view again. But it is more likely that our present studies will end by giving us a more accurate and adequate notion of the nature of force on the one hand and matter on the other. We shall see more clearly that force and matter are inseparable, and that in our use of these words we are merely making mental abstractions for the purpose of calculation. What was at one time considered to be inert matter was later found to be teeming with energy; so that this kind of matter, instead of being inert substance, was found to be the result of forces acting in some finer kind of matter. This finer kind of matter--hypothetical so far--was denominated "ether"; and should we succeed in examining this ether, we should probably find that it too is the result of forces acting in a still more recondite form of matter--a sub-ether, as it were. At all events we should have no choice but to describe it in that way. In the same way force must always be inseparably associated with mass, for the quantity denoted by the term "mass" is included in the definition of force. Thus the question whether electricity, magnetism, etc., are "forces" or "forms of matter" loses its meaning, since (strictly speaking) they cannot be either but must be both. The experiments mentioned seem to have shown that there is a definite physical unit of quantity for magnetism, just as the negative electron is said to be a definite unit of quantity for negative electricity. In this case we should have arrived at the conclusion that magnetic substances are those to whose atoms or molecules are attached these magnetic atoms.