206 28 



The calculations were carried out in the following manner: On account of the 

 special application of the dry cells, ii is, in the following equation, 



£ = 'f , (5) 



always equal to 2.9n volts, or "^ -^ abs. electrostatic units where n is a whole number 

 within the limits 1 to 10. 



The equation (5) may be written thus, 



_ 2.9ct 10000 _ 2.9 C b , 



^"■3000000^ [M 3000000 "■ ^' 



• n ' 



The factor — "^ is constant, therefore instead of calculating E, I confined myself 



30Ü0000 loOüO 



to calculating its proportional a -- — jy . In this manner the calculations are 



restricted to the determination of the reciprocal value of ^ in a table of reciprocals. 

 Then the values of a are corrected by subtracting the value of a corresponding to 

 the natural leakage in atmospheric air. Now the corrected values of a are marked 

 out as ordinales on millimeter squared paper, while the abscissae represent the 

 time reckoned from the introduction of the active gas into the ionisation chamber. 

 Through the points marked, an even curve is drawn, showing how a increases 

 immediately after the active gas is introduced into the ionisation vessel. 



In the case of radium emanation, the curve has a characteristic shape, so 

 that we are able from the form of the curve to decide whether the ionisation is 

 due to radium emanation or not. Of course, if the curve of a is to be taken as a 

 criterion as to whether the gas does or does not contain radioactive emanations 

 other than radium emanation, it is necessary to take care that the disintegration 

 products of the radium emanation are not carried along with the gas into the 

 ionisation chamber, as they will, on account of their ionising power, alter the 

 curve perceptibly. It is well known that the increase of ionisation immediately 

 after the introduction of the active gas, is due simply to the production of these 

 substances from radium emanation. 



If the ionisation due to the emanation or its proportional a, — which amounts 

 to the same, — is to be used as a measure of the amount of radium emanation, 

 then it is necessary to provide for a saturation current when the testings of leakage 

 are carried out; if not, the ionisation is not proportional to the leakage. In the 

 second place it must be remembered that the ionisation is a function of time. 

 Therefore it is only on condition that the ionisation is always tested at equal periods 

 after the introduction of the gas in question into the ionisation vessel, that it may 

 be depended upon to determine the amount of radium emanation in the gas. 



But when, as in our case, a considerable number of experiments in very 

 varying circumstances have to be carried out, it is exceedingly difficult in every 

 experiment consistently to test the ionisation at equal periods after the introduction 

 of the gas into the ionisation vessel. I have therefore, as already mentioned, pre- 



