264 Dunne — Heat Generated by Radio-active Substances. 



The strength of the electric current was '00019 ampere, and 

 the heat generated or absorbed "0016 calorie per hour. Iu ten 

 minutes "00027 calorie was generated or absorbed and this 

 quantity of heat displaced the image of the bubble about 

 l"6 inm . It follows that one millimeter displacement of the 

 image corresponds with "00017 calorie of heat absorbed or 

 generated. 



In some other experiments I have found that the displace- 

 ment of the bubble is proportional to the quantity of heat 

 absorbed or generated, provided that the absorption or genera- 

 tion is not too rapid. 



These results are used in estimating the small correction that 

 must be applied, if the value of the current that exactly 

 absorbs the heat generated by a source has been determined 

 only approximately. 



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Minutes 



I have measured the heat generated by radiothorium and by 

 polonium. These experiments were described in two notes 

 presented to the Paris Academy of Sciences on June 1 and 

 June 21, 1909. 



Since the first experiments I have measured the heat gen- 

 erated by the polonium several times to see if the heat effect 

 decreased with the time according to the law of decay of 

 polonium. Half a given quantity of polonium disappears in 

 about 142 days. 



The curves in figure 3 represent the displacement of the 

 bubble in these experiments, the dates being for curve 1 the 

 4th of May ; for curve 2 the 4th of June, and for curve 3 the 

 25th of June. In each case the lines ab and fg represent 

 the natural drift of the bubble. The abscissas of the points b 

 are the instants at which the polonium was lowered into the 



