244 Intelligence and Miscellaneous Articles, 



Now measurements made by one of us of the interferences on 

 the surface itself of the conducting wire show that in this case 

 there is no appreciable recession of the first node, and that there- 

 fore the part of the electrical tube immediately near the conductor 

 turns about the end of this almost instantly. But the distant 

 parts of the tube cannot traverse simultaneously the same angular 

 distance ; they remain behind and the electrical tube curves then 

 almost like the tail of a comet about the end of the wire (fig. 2). 



This would be the origin of this characteristic radiation pro- 

 ceeding from the end of the conductor, the existence of which we 

 may admit. It would follow from this that as the elements of the 

 tube continue to move at right angles to their direction for the 

 time being, the energy escapes from the end of the wire and is 

 lost in the surrounding space*. — Comptes Rendus, Nov. 6, 1893. 



DENSITIES IN THE EAKTH's CKUST. 

 To the Editors of the Philosophical Magazine and Journal. 



GrENTLEHElSr, 



Probably many of your readers will have read the Introductory 

 Eeview in Mr. Blake's ' Annals of British Greology ' for 1892, 

 and will, like myself, have been surprised at the very direct manner 

 in which he has impugned the accuracy of Mr. O. Fisher's 

 conclusions regarding the comparative densities and thicknesses of 

 those parts of the earth's crust which underlie oceans and con- 

 tinents respectively. 



Mr. Blake undertakes to show that Mr. Fisher's method " is 

 wholly fallacious." After stating the method referred to, he gives 

 three reasons from which "it is easily seen that this method 

 cannot lead to correct results." The manner in which these 

 reasons are expressed does not make it clear to the ordinary reader 

 that Mr. Blake has entirely upset Mr. Fisher's reasoning ; but when 

 he narrows the issue to " the definite point where the fallacy 

 comes in," the non-mathematical geologist must wish to know how 

 far Mr. Blake's mathematics are correct. 



I think that all who are interested in terrestrial physics 

 must hope that Mr. Fisher will either admit or deny the value of 

 Mr. Blake's criticism, and as he cannot reply in the ' Annals of 

 British Geology,' perhaps he will favour your readers with a note 

 on the subject, the issues being of considerable importance. 



A. J. Jukes-Browne. 



* There should "be an appreciable loss of energy on reflexion. "We 

 hoped to complete our research in this direction by measurements on the 

 wire itself (conf. Birkeland, Wied. Ann. vol. xlvii. p. 583). For three 

 wave-lengths X x = Qm, X 2 = 2'7 m, and A 3 = 1*2 m, we found the re- 

 flected wave respectively 0*6, 0*45, and 0*35 of the direct wave. But 

 we have devised another method of directly measuring the loss and we 

 have not again found these values, so that we only give them under 

 reserve, not having succeeded in explaining these contradictory results. 



