I2o U. S, BUREAU OF MINES NOTES. [J. F. I.

Therefore, it can not be truthfully said the United States produces no talcs equal iri quality to imported talcs. Unfor tu- nately many domestic consumers have been so thoroughly imbued with' the alleged superiority of imported talcs that domestic talcs have not been given a fair chance. In order to make the domestic product better known, the Bureau has issued a short report on the subject.

On the Displacement of Solar Rays Under the Action of 13ravitation.mH. BuISSON and CH. FABRY. (Comptes Rendus, April 25, 1921).--The Theory of Relativity predicts a shifting of the rays of the solar spectrum towards the red, in comparison with the same rays emitted by artificial sources. This is due to the gravitational field of the sun. Each wave-length should be lengthened by a little more than two-millionths of its terres- trial value.

As long ago as 1896 , Rowland and Jewell, at Johns Hopkins, found that there was a difference between the measured lengths ,of the same lines obtained in one case from the sun and in the other from the electric arc. In most instances the lengths of the solar waves were the greater, though the opposite occurred also. In I9o9, the authors showed that these latter anomalies disap- peared when comparisons were made with light emanating from an arc in a vacuum. At that time pressure was the sole cause known to be competent to produce a general shifting of the rays. Earlier in the present year Perot has shown that the b line of mag- nesium displays no noticeable shift due to pressure, and that the difference between its two wave-lengths according to solar or terrestrial origin agrees well with the predicted Einstein value.

The authors discuss 32 similar differences for as many iron lines, and conclude that they all similarly are in accord with the predicted values within the limit of experimental error. Thus, on the hypothesis that the pressure in the reversing layer of the sun is so small that it causes no shifting of the lines, it appears tha t the Einstein effect is competent to explain the difference be- tween the wave-lengths of the lines derived from the sun and from ,earthly sources.

G. F. S.