738 Mr. & Mrs. Soddy and Mr. A. S. Russell on the 



of a block of lead L, 10 cm. diameter and 5 cm. thick, in a 

 small hole in which the radium tube was placed at D, so that 

 the radium was in the centre and as near the surface as 

 possible. For experiments with uranium X another similar 



Fiff. 3. 



Notz 



Insulation thus 



Lead in Sect on thus \/////A 



Otner Sections tAus 



cite 



M 



M. 



Sec/7 on thro XX L) -Section throug h 



Seclionol P/on token through Z Z 

 rffi/iroximate Sca/e 



platform was used, with a rectangular depression 8 cm. x 

 4 cm. x 5 mm. deep, capable of taking the three platinum 

 trays on which the uranium X was spread in the form of 

 thin films. The apparatus was designed so that there should 

 be as little material as possible round the base and sides 

 of the ionization chamber, to produce secondary 7-rays 

 (Kleeman, Phil. Mag. 1908, xv. p. 639). But owing to 



