182 



SCIENCE. 



[N. S. Vol. XVII. No. 422 



published in full* before the appearance 

 of this account. 



The first results of a determination of the 

 Heat of Vaporization of Oxygen were re- 

 ported by Dr. J. S. Shearer. The method 

 used Avas an electrical one similar to that 

 already used by the author with liquid air. 

 The value obtained was 58.9. Experi- 

 ments to determine the heat of vaporization 

 of nitrogen were in progress, but not yet 

 completed. 



Professor R. W. Wood described and 

 exhibited a screen which was transparent 

 to ultra-violet light, while being opaque to 

 the rest of the spectrum. Such a screen 

 is very useful in photographing ultra- 

 violet spectra, since it enables the overlap- 

 ping spectra of other orders to be elimi- 

 nated. The author showed an interesting 

 lecture experiment in which the rays of 

 the lantern, after passing through such 

 a screen, were concentrated to an invisible 

 focus where a suitable fluorescent substance 

 was excited. The screen was made by 

 combining a gelatine film containing 

 nitroso-dimethyl-analine with copper oxide 

 and cobalt glass. 



A group of papers dealing with radio- 

 activity occupied the first half of the 

 Wednesday afternoon session and aroused 

 much interest. It is a subject for congratu- 

 lation that work along these lines is increas- 

 ing on this side of the Atlantic, and that so 

 many important papers dealing with the 

 subject should be presented to the Physical 

 Society. In a paper on the 'Magnetic and 

 Electrical Deviation of the Easily Ab- 

 sorbed Rays from Radium' Professor 

 Rutherford described experiments showing 

 that these non-penetrating 'a-rays' are 

 slightly deviated in passing through a mag- 

 netic field. The deviation is opposite in 

 sense to that of the cathode rays. The 

 deviation of the a-rays in an electric field 



* Physical Review, January, 1903. 



is also opposite to that of cathode rays. It 

 would, therefore, appear that these rays 

 are in all likelihood positively charged 

 particles. Both the magnetic and the elec- 

 tric deviations were very small. In order 

 to get results it was necessary to use in- 

 tensely active radium and strong fields. 

 The author's measurements indicate for the 

 velocity a value of about 2.5 X 10* cm./sec, 

 and for the ratio of charge to mass the 

 value 6 X lO'. It would thus appear that 

 the a-rays are similar in character to the 

 ' canal rays ' of the vacuum tube, the size of 

 the particles constituting the rays being 

 comparable to the size of atoms. The au- 

 thor pointed out that this result is in har- 

 mony with the fact previously observed 

 that the coefficient of absorption of a sub- 

 stance for such rays depends upon the 

 thickness of the absorbing layer already 

 traversed and increases rapidly with this 

 thickness. 



An article by Professor Rutherford and 

 Mr. S. L. Cook, on a 'Penetrating Radia- 

 tion from the Earth's Surface,' gave the 

 results of experiments which indicate that 

 part at least of the so-called spontaneous 

 ionization of air in a closed place is due to 

 radiation from outside. It was found that 

 in a closed vessel surrounded by a screen of 

 lead one inch thick the ionization was re- 

 duced to 68 per cent, of the value obtained 

 without the lead. The results indicated 

 that the rays, which were in part absorbed 

 by the lead, proceeded from all directions 

 and originated at or near the surface of 

 all bodies in the neighborhood. The au- 

 thors were of the opinion that the ionization 

 tip on the interior of a closed vessel was due 

 in part also to a radiation proceeding from 

 the surface of the surrounding vessel. This 

 was made probable by the fact that a screen 

 of iron seemed to be more effective in re- 

 ducing the ionization than one of lead, 

 while if the vessel containing the air was 



