Heating Effect of the y Rays from Radium. 625 



The two flasks were connected with a U-tube containing 

 xylene, and were immersed in a large water-bath. The whole 

 was placed in a constant- temperature room in the basement 

 of the building and the xylene level was read by means of a 

 Pye microscope with a micrometer eyepiece. The difference 

 between the levels in the two limbs of the U-tube was obtained 

 each time. Systematic time-interval readings were made of 

 one hour each so as to allow ample time for the metals to adjust 

 themselves to the various temperatures. 



We were surprised to find how sensitive the arrangement 

 really was, and how constant the readings were for such 

 minute sources of heat. 



The method of making an experiment was very simple. 

 The radium bromide was carefully weighed, and enclosed in a 

 small brass capsule, closed by an accurately screwed cover, to 

 which a fine thread was attached. The capsule was not more 

 than 3 mm. wide and 15 mm. long, and enclosed 23*7 mg. of 

 pure radium bromide. Having closed the flasks at atmospheric 

 pressure, the radium tube was inserted in the lead-encased 

 glass tube on one side, and after half an hour the first reading 

 of the xylene levels was made. The radium tube was then 

 transferred to the corresponding lead-covered glass tube in 

 the other flask, and after exactly one hour the second reading- 

 was made. Then followed alternate readings accurately at 

 hour intervals, until a sufficient number of readings were 

 obtained. Usually a whole day was devoted to one set of 

 readings. 



Having found the difference in level of the xylene columns 

 in each case after transferring the radium tube, the sum of 

 these gave the total effect. The observations with the 

 heating-coil were carried out in a similar manner, and gave 

 the necessary data for calculating the heat emission. A 

 constant heating current of '0068 ampere was used throughout, 

 and hence, by taking the ratio of the reading with the radium 

 and with the coil, it could be seen at once whether any 

 increase in heat emission had taken place when the aluminium 

 cylinders were replaced by the lead. 



In the case of the aluminium cylinders, the following 

 readings were obtained from radium bromide : — 



Mean reading 

 dumber of in divisions 



Date. observations. of microscope. 



November 9th 4 9*40 



11th 6 8-97 



14th 4 9-27 



16th 6 8*97 



Average value . . . . 9' 15 



