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In my communication to the meeting of February of this year (see these Proceedings, Vol 15, page 1297) I pointed out that the existence of spectroscopic doubles whose motion obeys the laws of *Kepler*, is incompatible with the theory of *Ritz*, while in agreement with that of *Lorentz*.

Since then Messr. P. *Guthnick*^{[1]} and E. *Freundlich*^{[2]} have brought forward the hypothesis that the velocity of light might depend on the velocity of the source in a manner differing from the simple addition postulated by the theory of *Ritz*. The most simple hypothesis would be

where *v* is the velocity of light emitted by a source having the velocity *u*. The problem then is no longer to decide whether or , intermediate values being excluded, but to assign an upper limit to .

We have then, using the notations of my former paper

If the true orbit is a circle, then the equation (1) becomes:

(1) |

If is very small we find for the equation (2) the following approximate expression

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