146 Mr. 8S. J. Allan on the 




Tasxe IL. 
| Percentage of unabsorbed rays. 
No. of layers 
of Aluminium. | 
Cotton ashes. Leather. | Felt. 
ab O Renae ue | 100 | 100 100 
pate eae Se | 66 | sk ROC 66 
iy 92 eee ieee 44 | 45 54 
OP eh US. 31 33 38 
1 eee Sree 19 p22 30 
8 5 a ey ee 12 14 | 22 
(ph h Sedna den kin 4 5°8 15 
NO were Be Paes, 15 18 11 
Ze Apt PY ets) 13 1°5 8 
Negri. sais ade 1:04 1:33 ae 
A ile Saline ies aN 8 1-01 5 


absorbing material, will be given by the equation 
I = Lens 
I, is the intensity at the surface before any absorbing layer 
is laid on, » being the coefficient of absorption of the material 
considered. If the absorption is proportional to the density, 
then the sabitye es should be a constant. 
density 
A number of substances were tried to test this point. It 
was difficult to get the solids in sufficiently thin layers to give 
enough ionization to work with. The @ rays produced too 
little ionization for accurate measurement. The experiments 
were performed in the same way as already described, the 
solids tested being mica, celluloid, paper, aluminium, brass, 
tinfoil, silver, and Dutch-metal. The value of X tor each 
substance could be easily calculated from the curves of ab- 
sorption. The results are shown in the following table. 







Tasie TTL; 
| | 
/ / r 
Substance. r. | Density. (en 
Gta eee 1080s 2-78 390 
Haeligloid 2c en ae 490 1-2 409 
(Seeuer “hi5 3.0251) eae 280 0-7 400 
Alnminium 23522.52.! 1050 26 403 
rasa: 3s ike eee 1195 86 140 
id keh ort Dn) Nis 1500 | re 205 
Bale i) ord eee epee gato be Bs 7100 10°5 680 
| Dutch-metal ......... 3000 9:0 330 | 
| | 


From an examination of these results it will be seen that 
