on the Temperature of the Sun. 439 



nometer should have been 0*1444 division. Thus we have for 

 pile No. 1, 



0-14-44- 

 No. 1 = ^| =0-0014665. 



The constants a and b have therefore to be multiplied by 

 the two reduction coefficients 0*359 and 0*0014665 in order 

 to obtain the new constants m and n, I have used the formula 

 thus obtained in my experiments with pile No. 1. For this 

 pile, then , we have the following formula : — 

 y = mT 2 (T-0)-n(T-0), 



log m = 1*2466088-10, 



logn =5*5254189-10, 

 on condition that the pile be placed at a distance from the 

 radiating body equal to 107*17 times the diameter of the body, 

 so that it shall appear, like the sun, at an angle of 31' 3 // *6. 



V. Verification of the Applicability of the Formula for Tempe- 

 ratures above 300°. 

 Color imetrical Experiments. — These experiments were made 

 in order to ascertain whether the formula continues to repre- 

 sent correctly the thermal effect of the radiation of bodies when 

 their temperature exceeds 300°. The first experiment was 

 made with a sheet of copper covered with lampblack and 

 heated by a spirit-lamp. This was one of the sources of heat 

 employed by Melloni, according to whom the copper has a 

 temperature of about 400°. Other physicists affirm the tem- 

 perature to be 390°. On introducing the value of the deflec- 

 tion on the galvanometer, obtained with pile No. 1, into the 

 formula, I obtained, from two successive experiments, numbers 

 between 390° and 400°. As the temperature of the sheet was 

 probably slightly different in the two experiments, I regarded 

 the result of this first trial as satisfactory. It was necessary, 

 however, that some more conclusive experiments should be 

 made at temperatures which were higher, but which could 

 nevertheless be determined by calorimetric methods. I there- 

 fore took a ball of copper heated to redness, the temperature 

 of which was estimated by means of a calorimeter constructed 

 for high temperatures. I suspended the copper ball by means 

 of a fine platinum wire in the flame of a large Wiessnegg 

 burner. The centre of the ball was in the line passing hori- 

 zontally through the centres of the holes of the screw-nuts 

 and through the centre of the face of the pile No. 1. In the 

 circuit of the latter was included, as usual, the Wiedemann's 

 galvanometer ; and the temperature of the ball was considered 

 to be constant when the galvanometric deflection remained 



