1NDEXE; 



T H IS 



LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[SIXTH SERIES.] * y 



MA Y 1905. 



LVIII. Heating Effect of the 7 Rays from Rttitimn. By 

 E. Rutherford, F.R.S., and H. T. Barnes, D.Sc, Pro- 

 fessors of Physics, McGill University, Montreal*. 



BY the experiments of Curie and Laborde f and others, it 

 is now well established that one gram of radium in radio- 

 active equilibrium continuously emits heat at the rate of 

 about 100 gram-calories per hour. Rutherford and Barnes J 

 showed that the emission of heat from radium was intimately 

 connected with its radioactivity, and was divided between 

 the different radioactive products of radium in proportion to 

 their a ray activity. These results indicated that the heating- 

 effect of radium and its radioactive products was mainly due 

 to the bombardment of the active matter (on the vessel con- 

 taining it) by the stream of a particles which are continuously 

 thrown off. One of us has calculated that the energy of the 

 ft ] (articles emitted from radium is only a small percentage 

 of th<* energy of the a particles. This conclusion is supported 

 by the experiments of P. Curie, who found that only a small 

 increase of the heating effect of radium was observed when 

 the radium was surrounded by one millimetre of lead — a 

 thickness sufficient to absorb a large proportion of the ft 

 particles. The total ionization which results from a complete 

 absorption of the ft and 7 rays in the gas, is in each case only 



* Communicated by the Authors. A preliminary account of the results 

 of this investigation was communicated in a letter to ' Nature,' p. 151 

 Dec. 15, 1901 



t Curie and Laborde, Comptes Rendus, cxxxvi. p. 673 (1903). 



X Rutherford and Barnes, Phil. Mag. Feb. 1904. 

 Phil. Mag. S. G. Vol. ( J. No. 53. May 1905. 2 T 



