January 30, 1903.J 



SCIENCE. 



U 



sunk in a tank of water the action conid 

 be reduced still further. The assumption 

 that iron and water radiate less strongly 

 than lead would explain these results. In 

 the case of lead the presumably more com- 

 plete absorption of the rays from outside 

 is more than balanced by the increased 

 radiation from the metal itself. 



Professor McLennan, of Toronto Uni- 

 versity, reported the results of experiments 

 made at the foot of Niagara Falls to de- 

 termine the induced radioactivity at that 

 point. An insulated wire mounted im- 

 mediatelj' at the foot of the falls on the 

 American side and maintained at a nega- 

 tive potential was found to acquire a much 

 less induced activity than would be ac- 

 quired by the same wire under similar 

 circumstances at Toronto. It was found 

 unnecessary actually to charge the wire 

 when at the foot of the falls, since it re- 

 ceived a negative charge from the air or 

 spray, the potential being about that 

 needed for the experiment. The activity 

 acquired at the foot of the falls was found 

 to be only about one sixth of that ob- 

 tained at Toronto. The author also de- 

 scribed experiments made in the neighbor- 

 hood of a static machine in operation. It 

 was found that the activity acquired by 

 a metal disk when placed near the machine 

 and negatively charged was much less than 

 when the same disk was placed at a greater 

 distance. It was also found that the ac- 

 tivity acquired by a body placed in a 

 closed room diminished with time. 



A paper by Professor McLennan and 

 Mr. E. F. Burton on the 'Electrical Con- 

 ductivity of Air' dealt with experiments 

 somewhat similar in character to those de- 

 scribed in the paper by Rutherford and 

 Cook mentioned above. It was found that 

 air placed in a closed vessel showed at first 

 a rapid diminution in conductivity, but 

 that later its conductivity increased again. 



The effect was moi-e marked at greater 

 pressures. The general form of the curve 

 showing the variation of conductivity was 

 the same for vessels made of different ma- 

 terials, but the initial diminution and sub- 

 sequent increase of conductivity were much 

 more marked in some than in others. The 

 authors think that the result is due to an 

 emanation or radiation issuing from the 

 walls of the containing vessel. The rapid 

 decrease in conductivity at first is due to 

 the dying out of the conductivity origin- 

 ally possessed by the air, while the subse- 

 quent increase is the result of the emana- 

 tion or radiation from the walls. It will 

 be noticed that this conclusion is practically 

 the same as that reached by Hutherf ord and 

 Cook. The fact that the results of these 

 entirely independent experiments should 

 be announced at the same meeting of the 

 Physical Society presents an unusual and 

 interesting coincidence. 



A paper on the 'Radioactivity of 

 Freshly Fallen Snow, ' by Mr. S. J. Allen, 

 showed that snow, like rain, possesses 

 marked radioactivity, which, however, is 

 rapidly lost. The activity of snow was 

 found to fall to one half its initial value 

 in thirty minutes. If the snow is melted 

 and the resulting water evaporated some- 

 thing possessing radioactivity is left be- 

 hind. The radiation from snow consists 

 chiefly of the easily absorbed rays. In 

 the discussion of this paper Professor Mc- 

 Lennan stated that he had found that after 

 a fall of snow a negatively charged wire 

 acquired less activity than before the snow- 

 storm. It would seem as though the active 

 constituent of the atmosphere had been re- 

 moved by the snow. 



In a paper ' On the Double Refraction of 

 Dielectrics in a Magnetic Field in a Direc- 

 tion at Right Angles to the Lines of Force, ' 

 by D. B. Brace, the author called attention 

 to the fact that the existence of double 

 circular refraction along the magnetic 



