Heating Effect of the 7 Rays from Radium. 627 



From the heating-coil we obtained as a result o£ six obser- 

 vations on Dec. 5th, 21*4 divisions with the same current as 

 before. The ratio of these numbers comes 1*723, which is 

 identical with the previous lead results, and agrees with the 

 aluminium to within 3 per cent. 



As a matter of interest, we removed the lead coverings and 

 used the uncovered glass tubes. The following observations 

 were obtained for radium: — 



Xumber of 



Date. 



observations. 



Mean. 



November 22nd 



. . . 4 



11-2 



23rd . 



. . . 10 



11-34 



28th . 



. . . 5 



11-8 



This gives an average of 11*45. 

 With the heating-coil we obtained : — 



Xumber of 

 Date. observations. Mean. 



November 24th .... 5 18*66 



26th .... 5 18*48 



This gives an average of 18*57 and a ratio to the radium 

 of 1*622, or a total heat emission from pure radium of 1-15 

 gram-calories per hour. The radical change in the conditions 

 of the experiment on removing the comparatively large surface 

 tor radiation in the shape of the metal coverings, probably 

 accounts for this value being different from the others by 

 7 per cent. 



The crucial test is, we think, the comparison of the heat 

 emission from the cylinders of aluminium and lead. 



It i< a matter of interest to compare the readings obtained 

 for the different metals. The thermal conductivity of the 

 aluminium is about four times as great as that of lead, and hence 

 the average temperature of the former would be less than for 

 the latter. The air in the flasks is heated chiefly at the metal 

 surfaces, and the variation of the readings in the case of the 

 Lead and aluminium cylinders is probably due to the differences 

 in the amount of heat escaping from the flat ends of the 

 cylinders. In all cases the readings from the heating-coil 

 showed a corresponding change, showing conclusively that this 

 increase had nothing to do with the absorption of the 7 rays. 

 Moreover the observations show a small diminution in heat 

 emission from the lead> over the plain glass where only a small 

 fraction of the ft and 7 rays were absorbed. We must conclude 

 from our experiment- that the 7 rays contribute but a very 

 small fraction of the total heat emission of radium, and that the 

 apparent increase observed by Paschen must be explained by 

 other causes. 



