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



If the heating effect of radium B were 5 per cent, of 

 that contributed by C, the discrepanc} r between theory 

 and experiment would be quite marked, and would indicate 

 that the heating effect of a product was not entirely a 

 measure of the energy of the expelled a particles and the 

 recoil atoms. 



In order to settle this point with certainty, it would be 

 necessary to isolate radium C from radium B, and to measure- 

 accurately its heating effect. It is hoped to continue expe- 

 riments in this direction, for the question to be settled is of 

 great importance in connexion with the general theory. 



§ 2. Heating Effect of the Radium Emanation. 



A series of experiments were made to determine accurately 



the heatino; effect of the radium emanation in absolute- 



measure in order to test how far the calculated heatino; effect 



is in agreement with experiment. The general method 



employed was similar to that described in the earlier part of 



the paper. A quantity of emanation of 100 to 150 milli- 



curies was concentrated in a small glass tube about 2*2 cm. 



long, 2 mm. bore, and of thickness 0*2 mm. This was 



attached to a long thin glass cylinder of small diameter for 



convenience of handling. In order to calibrate the heatino- 



© ©• 



effect observed, a coil of silk-covered manganin wire about 

 127 cm. long and 41*45 ohms resistance was wound uniformly 

 for a length of 2*2 cm. on a long thin glass tube of 2*5 nun. 

 bore. The heating-coil was of exactly the same length as 

 the emanation-tube, but in order to make sure that the heat 

 distribution was the same for the emanation-tube and for the 

 heating-coil, a copper cylinder 2*7 cm. long and 0'2 mm. 

 thick was placed over the heating-coil. The whole arrange- 

 ment was placed symmetrically in the glass tube of 5 mm. 

 bore, over which was wound one of the platinum balance 

 coils P (fig. 1). 



The procedure of an experiment was as follows. The 

 balance of the platinum coils was accurately adjusted and 

 the current through the coils kept constant. The emanation 

 tube in equilibrium with the active deposit was introduced 

 in the platinum coil in a definite position, and the maximum 

 deflexion of the galvanometer observed. A steady deflexion 

 was reached in less than ten minutes. The emanation-tube 

 was then withdrawn by the glass handle, and a known con- 

 stant current from a storage-cell passed through the manganin 

 coil to give nearly the same maximum deflexion as that due- 

 to the emanation. The current was then cut off and the 

 emanation^tube again introduced. Alternate measurements- 



