358 Prof. J. A. McClelland on the 
The Observations. 
We shall now give the numbers obtained in an experiment 
similar to a great number of others carried out, 
The capacity of the electrometer and the necessary con- 
nexions, including the vessel D, was 131 electrostatic units, 
or ‘000145 microfarad, and the electrometer gave a deflexion 
of 60 scale-divisions for 1 volt difference of potential between 
its quadrants. 
The admission of the radiam emanation produced a de- 
flexion of only 4 scale-divisions. 
The ionization current to D was then measured as described 
above immediately after the admission of the emanation. To 
sufficiently reduce the rate of movement of the spot of light 
a capacity of *1 microfarad was joined to the electrometer, 
and the deflexion was then 100 scale-divisions in 47 seconds. 
The admission of the air containing emanation into the 
vessel D produced, as stated, a small deflexion of 4 scale- 
divisions. Preliminary observations had been made to see if 
any deflexion would be produced when an equal quantity of 
air free from emanation was admitted in the same way. It 
was found that a small deflexion was produced probably 
by some friction effect, the deflexion varying in different 
experiments between 0 and 5 scale-divisions, and being always 
in the same direction. The direction of the deflexion of 4 
divisions obtained when the air contained emanation was the 
same as that obtained without emanation. 
Judging not only from this particular experiment, but 
from several others, we are safe in saying that the emanation 
did not carry a char ge sufficient to produce a deflexion of 
more than 1 scale-division. 
The experiment did not, therefore, detect any charge 
on the emanation ; but it is important to calculate whether 
or not the emanation might be charged, and the charge be 
less than what could have been detected in the above 
experiment. 
Let us suppose that each emanation particle has a charge 
equal to that carried by the gaseous ion ; we have no case of 
a charge less than this, so that if the emanation is charged 
its charge is probably at least equal to that of the gaseous ion, 
and may be greater. Denote this charge by e in electro- 
magnetic units. 
The capacity of the electrometer and connexions was. 
"000145 microfarad, and 1 scale-division cole ae to a 
potential-difference ‘between the quadrants of ¢, of a volt. 
A deflexion of 1 scale-division would therefore be produced 
