SECTION III., 1907. [19 ] Trans. R.S. C 
IV.—On the Amount of Radium Emanation in the Atmosphere near the 
Earth’s Surface. 
By A. S. Eve, M.A. 
(Communicated by Professor E. Rutherford, and read May 15, 1907). 
It has been proved by Elster and Geitel that a negatively-charged 
wire, exposed for a few hours in the air, receives a radio-active deposit 
similar in character to the quick-changing products of radium. Radium 
is known to be widely distributed among all the constituents of the 
earth’s crust. It is, therefore, probable that the emanation produced 
from the radium in the earth diffuses through the soil and enters the 
atmosphere. And if that is the case, not only can we account for 
the presence of the active deposits which have been discovered in the 
air, but we find also an explanation of the fact that the air is in a state 
of ionization. The conductivity of the atmosphere, due to ionization, 
must play an important part in electric, and therefore to some extent 
in meteorological, phenomena. 
It is, therefore, important to measure as accurately as possible 
the quantity of radium emanation in the atmosphere, expressed in 
terms of the quantity of radium required to maintain this supply of 
emanation at a constant rate. The present writer has already made 
an estimate of the quantity, by an indirect method,* in the following 
manner:—On the ground in the campus of McGill University was 
placed a large zine cylinder with closed ends and of known volume. 
Along the axis was a wire, charged negatively to about 10,000 volts, 
ors which was collected the: active deposit in the air in the cylinder. 
The activity of this deposit was measured with a gold-leaf electro- 
scope, which had been calibrated by the active deposit collected from 
the emanation from a known quantity of a standard solution of radium. 
By this comparative ‘method it was found that a cubic kilometre of 
air contained the active deposit which could be obtained from the 
emanation arising from .14 grams of pure radium bromide. In other 
words, 1 c.c. of the atmosphere appeared to contain the emanation from 
8.2X10 17 grams of pure radium; but there was no definite direct 
evidence of the existence of the emanation in the atmosphere. 
In the autumn of last year Professor Rutherford discovered that 
charcoal, made from the shells of cocoanuts, completely absorbed all 
the known radio-active emanations, when these were passed slowly 

*Phil. Mag., July, 1905. 
