# 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 $\left(1-v^{2}/c^{2}\right)^{\frac{1}{2}}$.