360 Prof, J. A. McClelland on the 
A more sensitive electrometer was used, and the quantity 
of emanation was also somewhat increased. An electrometer 
of the Dolezalek type was employed giving a deflexion equal 
to 4500 scale-divisions per volt difference of potential between 
its quadrants. With this sensitiveness the capacity of the 
electrometer and connexions was 900 electrostatic units, or 
‘OO1 microfarad. 
This electrometer was used to detect the charge on the 
emanation, and the ionization in the vessel D, after the 
emanation is admitted, was measured by the electrometer 
previously used. The small deflexion produced when air 
free from emanation was admitted into D was made as small 
as possible before the sensitive electrometer was used, and it 
was finally got rid of to such an extent that the deflexion 
was never greater than 10 divisions. varying in different 
experiments between 2 or 3 and 10 divisions, and being 
always in the same direction. 
We shall give numbers observed in one experiment, using 
the sensitive apparatus. 
The defiexion on the Dolezalek was 10 divisions when 
the emanation was admitted. The other electrometer was 
then used to measure the ionization, and gave 100 divisions 
in 77 seconds, with a capacity of *5 microfarad joined to it, 
the sensitiveness being the same as before, 60 divisions for 
1 volt difference between its quadrants. 
I’'rom this experiment and several similar ones we are safe 
in saying that in this case not more than 4 divisions of a 
deflexion are produced by the emanation. It is difficult to 
be certain of a smaller deflexion, the spot of light not being 
so steady as with a less sensitive instrument. 
If we make a calculation of the same nature as before, we 
find that either the emanation is uncharged or else each 
emanation particle must be producing by its radiation at least 
12,000 ions per second. 
Even this radiation might be looked upon as quite possible, 
so that the question whether the emanation is charged or not 
would not be settled. We have, however, good reasons for 
believing that only a small fraction of the total emanation 
particles are at any instant acting as centres of radiation and 
ionization. The ionizing power of emanation contained in a 
closed vessel falls off with time in a geometrical progression, 
showing that the rate of decay of the ionizing power is 
proportional to the ionizing power at every instant, a result 
which readily admits of the interpretation that the radiation 
arises from the emanation particles undergoing some change, 
