Maech 6, 1896.] 



SCIENCE. 



351 



tails were given of many experiments on these 

 X-rays. Its general effect was, however, to 

 show that, while many interesting points have 

 been noted, the obscurity hanging over the 

 subject had not been appreciably lightened. 

 Considerable differences of opinion were mani- 

 fest even upon the conditions of the Rontgen 

 experiments. While some advocated the use 

 of very powerful currents, others had been suc- 

 cessful with relatively weak ones ; and while 

 some were in favor of regarding the phosphores- 

 cence of the glass as the efficient source of 

 the rays, others ascribed them, to the glow of 

 the electrodes. A new turn was given to the 

 discussion by Captain Abney, who ventured, 

 amid some expressions of dissent, to doubt 

 whether the action of the Rontgen rays on a 

 sensitive plate could properly be described as 

 photographic. He cited several facts which, in 

 his opinion, excluded the theory of direct pho- 

 tographic action in any ordinary sense, and in- 

 dicated some preference for the view that the 

 Rontgen rays acted by first setting up phos- 

 phorescence or action of some unknown kind in 

 the glass at the back of the sensitive film. This 

 view was corroborated by an experiment de- 

 scribed by Prof Dewar upon platino-cyanide of 

 ammonium at low temperatures. This salt, 

 ordinarily fluorescent, only became phosphores- 

 cent at the temperature of liquid air. On be- 

 ing exposed to Rontgen rays, instead of the or- 

 dinary light, while immersed in liquid air, it 

 showed when the liquid air was poured off 

 brilliant phosphorescence. This proved that 

 whatever might be the nature of the Rontgen 

 rays, they were convertible into the light rays 

 aflfecting the human eye. A large number of 

 experiments were also described by Prof. Dewar 

 showing that resistance to the passage of 

 Rontgen rays increased with increase of atomic 

 weight. Organic substances were all relatively 

 transparent, following the carbon, oxygen, hy- 

 drogen and nitrogen of which they are com- 

 posed. Mere complexity of structure made no 

 difference, but substitution products showed 

 Increasing opacity in the order of the atomic 

 weights of the combined chlorine, bromine and 

 iodine. 



ASTRONOMY. 



- The Januarj' number of the monthly notices 



of the Royal Astronomical Society contains a 

 very interesting article by Messrs. Christie and 

 Dyson upon the progress of work on the Astro- 

 photographic Catalogue at Greenwich Observa- 

 tbry. It appears that up to the present time 

 no less than 160 plates for the Catalogue have 

 been measured. Moreover, at the present rate 

 of progress 180 plates are being measured an- 

 nually, and it is estimated that only five or six 

 years will be required to finish the Greenwich 

 zone. The precision of the Greenwich measures 

 is not quite as great as it might be, however, 

 because the authorities there prefer to sacrifice 

 some accuracy in order to expedite the pro- 

 gress of the work. We venture to doubt 

 whether this course is to be commended. It 

 is hardly in accord with the best traditions of 

 the Greenwich Observatory. Probably twelve 

 years devoted to this work, instead of six, 

 would have been suflScient to extract the very 

 highest accuracy possible from these photo- 

 graphic measures. 



Prof. Albrecht, of Potsdam, has now pub- 

 lished in the Astronomische Nachrichten the re- 

 sults of his researches on the Variation of Lati- 

 tude, to which we made reference in a recent 

 number. The former publication took place in 

 the report of the proceedings of the Interna- 

 tional Geodetic Committee, which is not very 

 accessible to the general astronomical public. 



H. J. 



GENERAL. 



We much regret to learn that the American 

 Meteorological Journal will be discontinued after 

 the forthcoming April number, which ends the 

 twelfth volume. The Journal has been carried 

 on at a financial loss on the part of the editors 

 ever since its foundation in 1884, and the pres- 

 ent step has been decided upon because there 

 seems no hope that it will become self-support- 

 ing, and because the editors do not wish any 

 longer to be financially responsible for a maga- 

 zine that has not secured the support which it 

 seems to them to have deserved. 



The series of the Catalogue of Scientific Papers 

 of the Royal Society, covering the years 1874- 

 83, has been completed by the publication of 

 Vol. XI. 



At a meeting of the Royal Photographic 



