Heating Effect of Radium and its Emanation. 317 



tigain obtained. Special experiments showed that any change 

 o£ balance was very slow and regular, so that a correction o£ the 

 readings for the small change o£ balance during the observa- 

 tions could be made with accuracy. The readings or the 

 galvanometer were remarkably steady, and observations of the 

 deHexion could be made to about J of a scale-division. 



A typical example showing the variation of the deflexion 

 with time for the first 18 minutes after removal of the 

 emanation is shown in fig. 3, curve E + A + B + C. 



Fiff. 3. 



100 



so 



so 



k 70 



60 



50 



40 



30 





















1 











i 







\ 

















X 



\ 

















-, \ 



















A. 



Vv 

















\ * 



c K 

 i v < 













\ 



<> 





"^f— 











c 







j 





i i 



C 



8 10 



Al inures. 



IS 



On account of the lag of the apparatus, the deflexion of 

 the galvanometer at any moment is always greater than cor- 

 responds to the heat emission of the emanation- tube. A 

 •number of experiments were made to determine the amount 

 of this lag. For this purpose a manganin coil was wound on 

 .a glass tube of the same size and thickness as the emanation- 

 tube T and introduced into the platinum coil. A current 

 from an accumulator was sent through this coil so as to give 

 an effect of about the same magnitude as that of the emanation 

 used in the experiments. The circuit was then broken and 

 the decrease of deflexion with time was noted. For this 

 coil the deflexion fell to half value in about 45 seconds, and 

 after that decreased approximately according to an expo- 

 nential law with a half-value period of about 30 seconds. 

 The lag of the manganin coil was found by experiment to be 



