on the Temperature of the Sun , 



329 



Table I. 

 Surrounding temperature 23 0, 8 C. 







Difference between 





Number of 

 experiment. 



Temperature of 



temperature of 



Deviations ob- 



the radiating 



radiating face 



served on the 



face. 



and surrounding 



galvanometer. 







temperature. 





1 



o 

 56-6 



o 

 32-8 



10-0 



2 



96-6 



72-8 



29-5 



3 



116-6 



92-8 



42-8 



4 



136-6 



112-8 



550 



5 



156-6 



132-8 



72-5 



6 



176-6 



152-8 



91-5 



7 



196-6 



172-8 



116-7 



8 



216-6 



192-8 



141-9 



9 



246-6 



212-8 



169-5 



10 



256-6 



232-8 



2040 



11 



276-6 



252-8 



239-5 



12 



296-6 



272-8 



283-5 



It should be stated that each experiment was repeated at 

 least twice, and that the necessary precautions were taken to 

 keep the temperature constant during the experiment. 



III. Empirical Formula, and the Choice of the one which best 

 represents the Phenomenon. 



It was important to determine from these experiments the 

 law according to which the thermal effect produced by radia- 

 tion varies with the temperature of the radiating surface. For 

 this purpose I constructed a curve from the preceding Table, 

 taking for abscissae the numbers contained in the third column, 

 and for ordinates the corresponding numbers of the fourth 

 column. A simple inspection of the curve showed that the 

 thermal effect of the radiation increases much more rapidly 

 than the temperature of the radiating surface, and therefore 

 Newton's law, which is expressed by a straight line, is not ap- 

 plicable here. In fact it has long since been shown that New- 

 ton's formula is only applicable when there is a small difference 

 between the temperature of the radiating body and the body 

 which receives the radiation. By a very careful series of ex- 

 periments Dulong and Petit proved that the law of radiation 

 is represented by the formula 



y = i(a'-'—l); 



