446 Prof. F. Rosetti's Experimental Researches 



VII. Verification of the Applicability of the Formula to Tempe- 

 ratures above 800°. 



If we call e the specific emissive power of the radiating 

 bodies, the formula becomes 



y = meT 2 (T-0)-n(T-0) ; 



and if the experiments be made with lampblack, e=l. 



In order to ascertain whether this formula be also applicable 

 when the temperatures are higher than those used in the calo- 

 rimetric experiments, I used the same experiments as those by 

 which e was determined, commencing with copper. I made 

 use successively of three disks of copper with the same dia- 

 meter of 10 millims. The first had a thickness of 1 millim., 

 the second of 2 millims., and the third of 3 millims. It is certain 

 that each different disk when placed in the flame acquires a 

 different temperature, the smallest attaining a higher tempe- 

 rature than the other two : if a disk were made any smaller 

 (as, for example \ of a millimetre), it would soon become red 

 hot and begin to melt. Now we know the melting-point of 

 copper is 1050° ; and therefore we may conclude that the 

 smallest of the three disks acquires in the flame a temperature 

 of about 1000°. The following results were obtained : — 



Sept. 3. — Copper disk blackened, with thickness 1 millim., 

 diameter 10 millims., placed at 438 millims. from the pile ; 

 the surrounding temperature being 28° C. : = 273 + 28 = 301° ; 

 the deflection on the galvanometer = 15*9. Calculating the 

 deflection on the galvanometer, supposing the pile were at a 

 distance of 107*17 + 10 millims., we obtain 



y — 2*6554 divisions. 



Introducing this value into the formula, as in the case of E = 1, 

 we have 



T=1260°, £=987°. 



In another experiment I obtained : — 



Sept. 26. — Copper blackened; thin disk (1 millim.); dis- 

 tance from the pile 163 millims.; surrounding temperature 

 18°; (9=291°; deflection of the galvanometer = 108*0 : 



t/ = 2*498, T=1233°*5, ; = 960°*5. 



I made two experiments with the disk of thickness 2 mil- 

 lims.: — 



Dec. 1. — Copper blackened; thickness of disk 2 millims.; 

 distance from the pile 150 millims. ; surrounding temperature 

 11°; (9 = 284°; deflection of galvanometer 121*8 : 



