Gases contained in Small Vessels. 563 
These results cannot be represented by a smooth curve ; 
but this could hardly be expected, as the value of the ioniza- 
tion, even after the maximum is reached, varies considerably. 
The increase during the first days is, however, quite certain, 
as the average for the first four days is always at least 
20 per cent. lower than that for any later four days, and as 
the leak in a vessel is always reduced, when old air is re- 
placed by fresh air. 
This increase of the conductivity might be due to a radio- 
active emanation which is given off by the walls at a constant 
rate ; on this supposition the leak at any time ¢ after refilling 
the vessel would be represented by the formula 
L=1,(1—e—, 
where A is the radio-active constant of the emanation and I, 
the final ionization after a long time has elapsed. It is, how- 
ever, not possible to compare the above results with the 
formula, or with the behaviour of any known radio-active 
substance, on account of the irregularities mentioned. 
The electroscope-method is in this case unsatisfactory, 
since it does not allow the leak during a short period to be 
measured. 
II. Observations at Different Pressures. 
As the ionization of air at atmospheric pressure is not 
constant, it could hardly be expected that observations at 
different pressures would show a better agreement. In fact, 
although the variations at lower pressures were on the whole 
smaller than at higher pressures, it was not possible to obtain 
values which lie accurately on a smooth curve. But these 
irregularities vanished on taking means of several observa- 
tions at each pressure. Another way of obtaining consistent 
results was to observe the leak at atmospheric pressure in a 
second bulb placed near the one in which the variation with 
pressure was measured, and to regard only readings during a 
time in which the leak in the control-vessel did not vary 
appreciably. Furthermore it was, of course, necessary to use 
only air which had been sufficiently long in the vessel to have 
reached the maximum of ionization. 
Tables V. and VI. contain the results of observations in 
two bulbs of 97 and 59 c.cm. capacity respectively. The 
values for the smaller bulb are averages of several independent 
observations each, as will be seen from the second column, 
the numbers for the larger bulb, however, were all obtained 
with the same sample of air, taking averages over 6 to 48 hours 
