324 Prof. Thomson, On Secondary Rontgen Radiation. 



secondary radiation comes from the liberation of the internal 

 energy of the atoms of the absorbing substance. This is con- 

 sistent with the result recently obtained by Professor Bumstead, 

 that when equal amounts of energy of primary radiation were 

 absorbed by lead and zinc, the heat produced in the lead was 

 greater than that produced in the zinc ; this points to the con- 

 clusion that, at any rate in the case of lead, the absorption of 

 primary Rontgen rays is accompanied by a change in some of 

 the atoms. 



