724 Prof. A. S. Eve on Changes in Velocity in an 
Using another book as screen the values for the radiators 
named, for a different arrangement from the above, were — 
Radiator. Ionization. 
None 3'00 
Lead 3*44 
Books 4*15 
Carbon 450 
Iron 4-60 
Cement 4*80 
Brick 5-00 
These results agree with the statement made in my first 
paper, that thick blocks of brick, slate, cement, granite, give 
rise to very penetrating rays. It can be proved that these 
rays come from considerable depths. With a book screen and 
carbon radiators the effects in divisions a minute were — 
Carbon. 
No. of Radiating Plates. Secondary Radiation. 
3-00 
1 3-48 
2 4-00 
3 4-52 
3 + a brick behind... 4'68 
Now these carbon plates were each 1*5 cm. thick. 
Again, with wood or slate radiators, 0*75 and 0'5 cm. 
thick respectively, the measured movements of the gold-leaf 
were, when the screen was 4 sheets of aluminium each 0*04 
<3m. thick, as follows : — 
No. of Sheets of :— 
Radiators. 
Wood (each 0'75 cui.). 
Slate (each 05 cm.). 
1 
642 
6-48 
6-50 
6-70 
6-85 
6-97 
6-96 
7-68 
8-37 
8-91 
9-42 
9-80 
2 
3 
4 
5 
6 
7 
8 
9 
