Mr Satterly, Radium-content of Cambridge Waters. 543 

 Table III. 



From Table III it follows that 1'57 x IG^^ gm. radium ac- 

 cumulates emanation at the rate of approximately 20"0 per day. 

 From this and Table II it follows that 



1 litre tap water contains 1'6 x 10~^^ gm. radium 



1 „ Cam „ „ 3-2 x W^ „ 



1 „ hydrochloric acid „ 11 x 11"^^ „ „ 



It may also be calculated that the emanation given off by the 

 initial boiling of one litre of tap water is that which would be in 

 equilibrium with 130 x 10"-'^ gm. radium, and of one litre of Cam 

 water that which would be in equilibrium with 5*0 x 10""^^ gm. 

 radium. 



For the water of the St Lawrence, as already stated, Eve* finds 

 a radium-content of "25 x 10~^^ gm. radium per litre, but he does 

 not state whether this result is obtained from the initial or sub- 

 sequent boiling. It follows, in either case, that the waters in the 

 neighbourhood of Cambridge contain a much greater quantity of 

 radium per unit volume than the waters in the neighbourhood of 

 Montreal. Naturally therefore the air at Cambridge would contain 

 a greater quantity of radium emanation than the air at Montreal. 

 The proportion actually found ■[- was 10 : 6. 



It may be mentioned in conclusion that the Cam takes water 

 which has drained through the Chalk deposits in the south of 

 Cambridgeshire, and then runs over the clayey deposits at the 

 base of the Chalk, while the water supply of Cambridge is taken 

 from springs issuing at Cherryhinton and Fulbourn from the 

 greensand which lies above the Gault and below the Chalk. 



Phil. Mag. July 1909. 



t ibid. Oct. 1908, July 1910. 



