Page:Aether and Matter, 1900.djvu/222

 by convection, that has been demonstrated for the electrostatic attractions of moving charges. Let us understand by $$S_1$$, and $$S_2$$, not as previously two systems of charged particles, but two systems of molecules,—the second at rest and the first in motion with velocity v in the direction of the axes of x,—between whose dimensions the previously given relation holds; then since in both systems the x components of the forces are the same, while the y and x components differ by the factors given, it is clear that the forces in $$S_1$$ will balance when that is the case for those of $$S_2$$. If therefore $$S_2$$ is the state of equilibrium of a solid body at rest, the molecules in S_1 have just those positions in which they could subsist under the influence of the motion of translation. The displacement into this new configuration would therefore take place of itself, involving a contraction in the direction of motion in the ratio of unity to $$\left(1-v^{2}/c^{2}\right)^{\frac{1}{2}}$$.

"In reality the molecules of a body are not at rest, but corresponding to each position of equilibrium they are in a state of stationary motion. How far this difference is of importance for the phenomena treated, must be left undetermined: the experiments of Michelson and Morley leave for it a comparatively wide range of effect on account of the unavoidable errors of observation."

The force of the last remark is removed by Michelson's more recent observations with a longer ray-path, in which the delicacy was so great that it was necessary for consistent results to get rid of the air; even then no trace of uncompensated effect was observed.

. In favour of the view that the interactions between atoms are in very great part those necessitated by the aether whose properties are revealed in electric and optical phenomena, there is, in addition to the inherent theoretical difficulty in conceiving any other kind of interaction, the actual fact that on the lines of the above argument such a view does account for a definite and well-ascertained experimental result, that of