604 



SCIENCE. 



[N. S. Vol. VIII. No. 201, 



ruled with 65,000 lines, to be polarized in 

 the reverse way. 



Further prosecution of these researches 

 must lead to deeper insight into molecular 

 processes and the mode in which they aifect 

 the ether; indeed, already valuable theoretic 

 views have been promulgated by H. A. 

 Lorenz, J. Larmor and G. F. Fizgerald, on 

 the lines of the radiation theory of Dr. 

 Johnstone Stoney ; and the connection of 

 the new phenomena with the old magnetic 

 rotation of Faraday is under discussion. It 

 is interesting to note that Faraday and a 

 number of more recent experimenters were 

 led by theoretical considerations to look for 

 some such effect ; and, though the inade- 

 quate means at their disposal did not lead 

 to success, nevertheless a first dim glimpse 

 of the phenomenon was obtained by M. 

 Fievez, of the Eoyal Observatory at Brus- 

 sels, in 1885. 



It would be improper to pass without at 

 least brief mention the remarkaWe series of 

 theoretic papers by Dr. J. Larmor, pub- 

 lished by the Royal Society, on the relation- 

 ship between ether and matter. By the 

 time these researches become generally in- 

 telligible they may be found to constitute a 

 considerable step toward the further mathe- 

 matical analysis and interpretation of the 

 physical universe on the lines initiated by 

 ISTewton. 



In the mechanical construction of Kont- 

 gen-ray tubes I can record a few advances, 

 the most successful being the adoption of 

 Professor Silvanus P. Thompson's sugges- 

 tion of using for the anti- cathode a metal of 

 high atomic weight. Osmium and iridium 

 have been used with advantage, and os- 

 mium anti-cathode tubes are now a regular 

 article of manufacture. As long ago as 

 June, 1896, X-ray tubes with metallic 

 uranium anti-cathodes were made in my 

 own laboratory, and were found to work 

 better than those with platinum. The dif- 

 ficulty of procuring metallic uranium pre- 



vented these experiments from being con- 

 tinued. Thorium anti-cathodes have also 

 been tried. 



Rontgen has drawn fresh attention to a 

 fact very early observed by English experi- 

 menters — that of the non-homogeneity of 

 the raj's and the dependence of their pene- 

 trating power on the degree of vacuum ; 

 ra\'S generated in high vacua have more 

 penetrative power than when the vacuum 

 is less high. These facts are familiar to all 

 who have exhausted focus tubes on their 

 own pumps. Eontgen suggests a con- 

 venient phraseology ; he calls a low- vac- 

 uum tube, which does not emit the highly 

 penetrating rays, a ' soft ' tube, and a tube 

 in which the exhaustion has been pushed to 

 an extreme degree, in which highly-pene- 

 trating rays predominate, a ' hard ' tube. 

 Using a ' hard ' tube, he took a photograph 

 of a double-barrelled rifle, and showed not 

 only the leaden bullets within the steel 

 barrels, but even the wads and the charges^ 



Benoit has re-examined the alleged rela- 

 tion between density and opacity to the 

 rays, and finds certain discrepancies. Thus, 

 the opacity of equal thicknesses of pal- 

 ladium and platinum are nearly equals 

 whilst their densities and atomic weights 

 are very different, those of palladium being 

 about half those of platinum. 



At the last meeting of the British Asso- 

 ciation visitors saw — at the McGill Uni- 

 versity — Professors Cox and Callendar's 

 appartus for measuring the velocity of Ront- 

 gen rays. They found it to be certainly 

 greater than 200 kilometers per second. 

 Majorana has made an independent deter- 

 mination, and finds the velocity to be 600 

 kilometers per second with an inferior limit 

 certainly of not less than 150 kilometers per 

 second. It may be remembered that J. J. 

 Thomson has found for cathode rays a veloc- 

 ity of more than 10,000 kilometers per sec- 

 ond, and it is extremely unlikly that the ve- 

 locity of Rontgen rays will prove to be less. 



