on the Temperature of the Sun. 443 



power of lampblack ; and taking the latter as unity, I thus 

 obtained the emissive power of the body under experiment. 



In the following section I shall make use of this method. 

 For the present, I need only mention that I obtained from my 

 experiments the number 0*943 to represent the emissive power 

 of copper surrounded by a flame. 



In the calorimetric experiments already mentioned, the bare 



ball of copper gave 1*322 



j 



If this ball had been covered with lampblack, the thermal 

 effect would have been 



*=<35 =i - 402; 



and the formula would give the value 



*=763*6. 



The values 



1-394 and 1-402, 

 762-1 and 763'6 

 are near enough to be satisfactory ; and we may therefore 

 conclude that the formula is applicable to high temperatures, 

 provided that the radiating surface be lampblack, or that the 

 specific emissive power of the radiating surface be introduced 

 into it. I have made my description of this experiment very 

 minute, in order to give an exact idea of the manner in which 

 I have conducted these researches. I made many other calo- 

 rimetric experiments, from which I obtained satisfactory results. 



VI. Method of determining the Specific Emissive Power of 

 Bodies at High Temperatures. 



I have invented a very simple and exact method of deter- 

 mining the specific emissive power of bodies at high tempera- 

 tures. Every body knows the form assumed by the flame of 

 a Bunsen's burner when the air is freely admitted. By my 

 researches on the different shapes of these flames (" Sulla 

 Temperatura delle Fiamme," Atti delR. Istituto Veneto, vol. iii. 

 1877), I have shown that in the higher part lying between the 

 apex of the interior cone and the summit of the exterior enve- 

 lope the temperature is not higher than 1200°. A body placed 

 in this space would have a temperature lower than that of the 

 flame, dependent upon several causes — viz. the mass of the 

 body, the specific heat, the conductivity, the emissive power, 

 and the conductivity of the wire or rod employed to support 

 the body. Nevertheless it is certain that, if the flame remains 

 constant, the same body placed in the same position will have 

 the same temperature in two successive experiments. 



Now, if in one experiment the surface of the bodv be bare 



2H2 



