438 Prof. F. Rosetti's Experimental Researches ■ 



siderable experience proved this method to be the most expe- 

 ditious, convenient, and accurate of those usually employed 

 for the separation of these metals. 



The experiments were made in Prof. Galloway's laboratory 

 at the Royal College of Science. 



October 1879. 



LIII. Experimental Researches on the Temperature of the Sun. 

 By F. Rosetti, Professor of Physics in the University of 

 Padua. 



[Continued from p. 332.] 



IV. Calculation of the Constants of the Formula in order to 

 render it applicable to the Experiments made with Pile 

 No. 1. 



THE object of my investigation was to ascertain the tem- 

 perature of the sun by applying the formula to experi- 

 ments made on solar radiation. In these, and in many other 

 experiments made on the radiation of very hot bodies, I em- 

 ployed the pile No. 1. The constants a and b, determined 

 for pile No. 2, had then to be modified in such a manner that 

 the same formula, with the new values of the two constants, 

 could be applied to the experiments made with pile No. 1. 

 For this purpose I made experiments by placing the two piles 

 successively in front of the Leslie's cube, kept at a constant 

 temperature of 312° C. 



Pile No. 1 produced 28° deflection, 

 Pile No. 2 „ 78° „ 

 giving 



No.l__28 



No. 2 -78-° 6 ™> 



i. e. pile No. 1 = 0-359 No. 2. 



Thus, in order to adapt the preceding formula to pile No. 1, 

 the constants a and b had to be multiplied by 0*359. I was 

 desirous, however, of so expressing the formula, that by 

 means of it the thermal effect of the sun on pile No. 1 could 

 be directly compared with the effect of the radiation from the 

 hot body observed under the same angle as the sun, i. e. 

 32' 3" *6. By placing the pile with its face 134 millims. from 

 the radiating surface of the Leslie's cube, which, by the inter- 

 position of a diaphragm, was limited to a circle of 32*65 mil- 

 lims. diameter, I obtained a deflection of 98*5 divisions on the 

 galvanometer. In order that the radiating surface should be 

 at the same angle as the sun, the pile should have been placed 

 at a distance of 3*499 metres. By making use of the law of 

 inverse squares, it is obvious that the deflection on the galva- 



