Vit] RADIO-ACTIVE EMANATIONS 231 
been kept negatively charged during the experiments, had most 
of the excited activity concentrated on their surfaces. These 
were removed, new rods substituted and the current immediately 
determined. The ratio of the currents in the half cylinders under 
these conditions was proportional to S, and S,, the amounts of 
emanation present in the two halves of the cylinder. 
The values of K, deduced from different values of t, were found 
to be in good agreement. In the earlier experiments the values 
of K were found to vary between ‘08 and ‘12. In some later 
experiments, where great care was taken to ensure that tempera- 
ture conditions were very constant, the values of K were found to 
vary between ‘07 and ‘09. The lower value 07 is most likely 
nearer the true value, as temperature disturbances tend to give 
too large a value of AK. No certain differences were observed in 
the value of A whether the air was dry or damp, or whether an 
electric field was acting or not. 
152. Some experiments on the rate of diffusion of the radium 
emanation into air were made at a later date by P. Curie and Danne’. 
If the emanation is contained in a closed reservoir, it has been shown 
that its activity, which is a measure of the amount of emanation 
present, decreases according to an exponential law with the time. 
If the reservoir is put in communication with the outside air 
through a capillary tube, the emanation slowly diffuses out, and 
the amount of emanation in the reservoir is found to decrease 
according to the same law as before, but at a faster rate. Using 
tubes of different lengths and diameters, the rate of diffusion was 
found to obey the same laws as a gas. The value of A was found 
to be 0100. This is a slightly greater value of K than the lowest 
value 0°07 found by Rutherford and Miss Brooks. No mention 
is made by Curie and Danne of having taken any special precau- 
tions against temperature disturbances, and this may account for 
the higher value of K obtained by them. 
They also found that the emanation, like a gas, always divided 
itself between two reservoirs, put in connection with one another, 
in the proportion of their volumes. In one experiment one reser- 
voir was kept at a temperature of 10° C. and the other at 350° C. 
1 C. R. 136, p. 1314, 1903. 
