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 THE HYPOTHESES RELATING TO THE LUMINOUS ÆTHER, AND AN EXPERIMENT WHICH APPEARS TO DEMONSTRATE THAT THE MOTION OF BODIES ALTERS THE VELOCITY WITH WHICH LIGHT PROPAGATES ITSELF IN THEIR INTERIOR.

BY M. H. FIZEAU.

hypotheses have been proposed to account for the phænomena of aberration in accordance with the doctrine of undulations. Fresnel in the first instance, and more recently Doppler, Stokes, Challis, and many others, have published memoirs on this important subject; but it does not seem that any of the theories proposed have received the entire assent of physicists. In fact, the want of any definite ideas as to the properties of the luminous æther and its relations to ponderable matter, has rendered it necessary to form hypotheses, and among those which have been proposed there are some which are more or less probable, but none which can be considered as proved.

These hypotheses may be reduced to three principal ones. They refer to the state in which the æther existing in the interior of transparent bodies may be considered to be.

This æther is either adherent, and as it were attached to the molecules of bodies, and consequently participates in the motions to which the bodies may be subjected;

Or the æther is free and independent, and is not influenced by the motion of the bodies;