general the same, how will this coefficient depend upon these two velocities?
Upon this subject we can only make hypotheses, but we are naturally led to investigate which of these hypotheses would be compatible with the principle of relativity. There are a great number of them; the only one of which I shall here speak is that of Lorentz, which I shall briefly expound.
Consider first electrons at rest. Two electrons of the same sign repel each other and two electrons of contrary sign attract each other; in the ordinary theory, their mutual actions are proportional to their electric charges; if therefore we have four electrons, two positive A and A´, and two negative B and B´, the charges of these four being the same in absolute value, the repulsion of A for A´ will be, at the same distance, equal to the repulsion of B for B´ and equal also to the attraction of A for B´, or of A´ for B. If therefore A and B are very near each other, as also A´ and B´, and we examine the action of the system A + B upon the system A´ + B´, we shall have two repulsions and two attractions which will exactly compensate each other and the resulting action will be null.
Now, material molecules should just be regarded as species of solar systems where circulate the electrons, some positive, some negative, and in such a way that the algebraic sum of all the charges is null. A material molecule is therefore wholly analogous to the system A + B of which we have spoken, so that the total electric action of two molecules one upon the other should be null.
But experiment shows us that these molecules attract