THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



JANUARY 1900. 



I. A Radio-active Substance emitted from Thorium Compounds. 

 By E. Rutherford, M.A., B.Sc, Macdonald Professor of 

 Physics, McGill University, Montreal *. 



IT has been shown by Schmidt f that thorium compounds 

 give out a type of radiation similar in its photographic 

 and electrical actions to uranium and Rontgen radiation. 

 In addition to this ordinary radiation, I have found that 

 thorium compounds continuously emit radio-active particles 

 of some kind, which retain their radio-active powers for 

 several minutes. This " emanation/'' as it will be termed for 

 shortness, has the power of ionizing the gas in its neigh- 

 bourhood and of passing through thin layers of metals, and, 

 with great ease, through considerable thicknesses of paper. 



In order to make clear the evidence of the existence of a 

 radio-active emanation, an account will first be given of the 

 anomalous behaviour of thorium compounds compared with 

 those of uranium. Thorium oxide has been employed in 

 most of the experiments, as it exhibits the " emanation " 

 property to a greater degree than the other compounds; but 

 what is true for the oxide is also true, but to a less extent, of 

 the other thorium compounds examined, viz., the nitrate, 

 sulphate, acetate, and oxalate. 



In a previous paper J the author has shown that the radiation 



* Communicated bv Prof J. J. Thomson, F.R.S. 



t Wied. Ann. May 1898. 



X Phil. Mag. Jan. 1899, p. 109. 



Phil. Mag. S. 5. Vol. 49. No. 296. Jan. 1900. B 



