McCiettanp—On the Emanation gwen off by Radium. 93 
if charged, each particle of the emanation must give out radiation sufficient to 
produce at least 1400 ions per second. If the radiation from each particle were 
less than this, then the number required to give the observed ionisation would be 
greater than what would produce 1 scale-division of a deflection. This number is 
calculated on the assumption that the charge on the emanation is the same as 
the charge on the gaseous ion; it is not probable that it is less than this, if charged 
at all; and if it is greater, the number 1400 would be correspondingly greater. 
It is, however, quite likely that each emanation particle may be capable of 
producing ions in the vessel D at the rate of 1400 per second. For this reason 
the test was pushed a step further. 
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 deflection 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 ‘001 microfarad. 
This electrometer was used to detect the charge on the emanation, and the 
ionisation in the vessel D, after the emanation is admitted, was measured by the 
electrometer previously used. The small deflection 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 
deflection 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 deflection on the Dolezalek was 10 divisions when the emanation was 
admitted. The other electrometer was then used to measure the ionisation, 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. 
From this experiment and several similar ones, we are safe in saying that in 
this case not more than 4 divisions of a deflection are produced by the emanation. 
It is difficult to be certain of a smaller deflection, 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 ionisation. ‘The ionising power of emanation contained in a 
