18 M‘Ciettanp—The Energy of Secondary Radiation. 
ANOTHER MertTHop oF CALCULATING THE RATIO DENOTED BY 1x 
Some results recently published by Professor Righi* afford another method 
of calculating the ratio of the energy of the secondary radiation to that of the 
primary radiation. Righi allowed 8 rays to fall on a plate placed in a well- 
exhausted vessel, and connected to an electrometer. ‘The plate got a negative 
charge ; but the rate of charging was found to depend on the material of which 
the plate was made, although the same radiation was absorbed by the plate in each 
case. Righi found that the higher the atomic weight of the substance of which 
the plate was made the slower did it charge negatively, this result arising from 
the fact that the higher the atomic weight the greater the emission of secondary 
8 particles. 
Righi’s paper gives the following numbers :— 
Substance. Negative Charge. 
Carbon, . pee : 53 
Aluminium, . : : : ' ; 46 
Sulphur, . : 45 
Iron, : : ; : ; : 43 
Nickel, . : ; 41 
Copper, . : : : 40 
Zine, : : ‘ : : : : 40 
Silver, . ; : ; ‘ ‘ 33 
Tin, : ; 32 
Platinum, ; : en ¢0) 
Lead, . ; ; : 26 
Bismuth, . : : : 23 
Now, if we let NW denote the number of primary £8 particles falling on 
the plate in unit time, and if », denote the number of secondary particles 
emitted when the plate is made of lead, we have 
I" = nh = 26a, 
where a is some constant. 
* Accademia dei Lincei, 21 Maggio, 1905. 
