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 PROFESSOR LARMOR in his analysis for a system moving through the aether has shown how first and second order effects may be annulled in certain optical and electrical tests of the aether drift. He has not shown, however, how to annul third and higher order effects: but he states, "if indeed it could be proved that the optical effect is null up to the third order, that circumstance would not demolish the theory, but would rather point to some finer adjustment than it provides for: needless to say the attempt would indefinitely transcend existing experimental possibilities".

Attention should therefore be called to the results in my experiment on the double refraction of water moving through the aether. The sensibility attained was such that the greatest difference in velocity or in index between the two components which could exist, referred to that of water for green light, $$\lambda=.00005$$ cm, was less than $$7.8\times10^{-13}$$ of the whole. If ($$10^{-4}$$) be taken as the third order magnitude, this result is then easily within the limit. It was not possible to attain this sensibility with a solid—glass; but, since the physical state of the substance does not enter into the theory under consideration, the results for a liquid should be equally valid.

The conclusion as to the amount of double refraction as deduced from what might be expected in comparison with accidental double refraction in a solid—glass, should not be considered as defining the mode and the amount of any double refraction arising from molecular reactions due to a system moving through the aether.

Granting the FitzGerald-Lorentz "contraction-hypothesis," we should have for this experiment a complete correspondence as regards molecular activities between the moving system thus shrunk and the same at rest, up to and including second order quantities, as the analysis of Larmor shows. But the negative results of such a third order test, showing as it does the absence of any difference between the moving and the fixed system, up to and including third order quantities, may