318 Prof. E. Rutherford and.Mr. H. Robinson on the 



slightly greater than the lag of the bare emanation-tube. It 

 was found that for a slow decrease of heating' effect the 

 deflexion lagged about one minute behind the actual heat, 

 emission. 



Analysis of the Curve. 



The curve given in fig. 3 is typical of a number of curves 

 obtained which agreed closely with one another. The re- 

 lative heating effects of the emanation and its products can 

 be deduced from the observed curve by comparison with the 

 theoretical curve of decay of the components of the active 

 deposit. 



The heating effect of the emanation itself has practically 

 disappeared three minutes after its removal. The variation 

 of the heating effect of the tube C resulting from the 

 removal of the emanation alone is shown in the dotted side 

 curve E E, where the maximum heating effect is taken as 

 29 per cent, of the total. This curve was deduced from a 

 knowledge of the cooling curve of the tube under the 

 experimental conditions when heated above its surroundings. 



After subtracting the heating effect due to the emanation 

 alone, the resulting curve A + B + C gives the heating effect 

 due to radium A-fB + C. After about 20 minutes the 

 heating effect due to radium A has practically vanished, and 

 the effect observed is then due to radium B + C. It was 

 found that the curve after 20 minutes followed closely 

 the theoretical curve to be expected if the heating effect was 

 provided mainly by radium C. Assuming this to be the case, 

 the heating effect due to radium alone is shown by the 

 curve C C, which cuts the axis of ordinates at 40. A lag 

 of 1 minute is assumed between the observed and true 

 heating effects after 20 minutes. The difference of the 

 ordinates of the curves A + B + C, and C C, must be due to 

 the heating effect supplied by radium A. After an initial 

 lag, the heating effect of radium A should ultimately decay 

 exponentially with its known period of transformation, viz. 

 3 minutes. This is shown clearly in the curve of fig. 4. The 

 difference-curve is plotted, allowing an initial interval of 

 3 minutes for the emanation effect to decay. Plotting the 

 logarithms of the deflexions as ordinates and the time as 

 abscissae., the curve is a straight line, showing that the heating- 

 effect due to radium A decays exponentially with a half- value 

 period of 3 minutes. The maximum heating effect of 

 radium A was deduced to be 31 per cent, of the total. 



The variation of heating effect of the emanation-tube with 

 time brings out clearly that about 29 per cent, of the initial 



