Letter | Published:

Relativity and Gravitation

Nature volume 101, page 126 (18 April 1918) | Download Citation



A MATHEMATICAL friend with whom I have been discussing Prof. Eddington's paper on “Relativity and Gravitation,” recently published in NATURE, has made what appears to me to be an interesting suggestion. Prof. Eddington states that if a current of æther were moving vertically (say) with a velocity of 161,000 m./sec, a rod 8 ft. long, when placed transversely to the stream (i.e. horizontally), would, when turned vertically, be only 4 ft. He also says that this contraction would be unobservable because the retina of the eye would have similarly contracted in a vertical direction. Suppose, however, that the rod in its two positions were observed, not directly, but by means of a mirror inclined at an angle of 45°, by a spectator lying on his back on the floor of the room? His retina, being horizontal, would, ex hypothesi, have undergone no contraction at all. Both images of the rod, in its horizontal and vertical positions, would fall on this horizontal retina. If the experiment could be performed the contraction of the rod ought to be evident, and afford direct proof of the Lorentz-Fitzgerald hypothesis. Is there any flaw in this reasoning?

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