on the Temperature of the Sun. 447 



the formula gives 



T=1211°, £=938°*0. 

 Dec. 6. — Distance from the pile 157 millims. ; = 284°; 

 deflection =113*5. 



# = 2*432, T = 1218°, £ = 945. 

 Disk of copper 3 millims. thickness : — 



Dec. 1. — Distance from the pile 150 millims.; = 284°; 

 deflection = 114*3 : 



# = 2*239, T=1190°*7, £ = 917°*7. 

 Dec. 6. — Distance from the pile 157 millims. 



# = 2*272, T=1196°*3, £=923°*3. 



The temperatures 987° and 960° obtained with the thin 

 disk, 938° and 945°, with the medium disk, and 917°*7 and 

 923°*3 with the thickest disk, were most probably their true 

 temperatures at the time of the experiment. 



Iron. — The disk of iron was very thin, 10 millims. in dia- 

 meter, and was covered with lampblack. 



Sept. 26. — Distance from the pile 163 millims. ; deflection 

 131*0; 0=291°: 



# = 3*030, T = 1308°*0, £ = 1035°. 

 Platinum. — The disk of platinum was very thin ; diameter 



10 millims.: 



# = 3*847, T=1410°, £=1147°. 

 Cylinder of Oxy chloride of Magnesium. — Diameter 6*1 mil- 

 lims. ; distance 163 millims. ; deflection 41*6; = 291°: 

 # = 4*091, T=1432°*5, £=1159°*5. 



To sum up, we find that the disks of copper acquired dif- 

 ferent temperatures according to their thickness : the thinest 

 disk attained the temperature of 987°, the next thicker one 

 945°, and the thickest 923°. The thin disk of iron reached 

 the temperature of 1035°, the disk of platinum 1147°, and the 

 cylinder of magnesium oxy chloride 1160°. We can under- 

 stand how the last-mentioned body may attain a higher tempe- 

 rature than any of the others ; for, being non-metallic, it is 

 not so good a conductor of heat as the others, and therefore 

 does not give up as much of its heat to the metallic support 

 or porcelain tube by means of which it is held. 



Experiments made with a Cylinder of Magnesium Oxy chloride 

 rendered Incandescent by means of a Flame of Coal-gas and 

 Oxygen. 

 The cylinder of magnesium oxychloride which I used in my 



experiments had a diameter of 6*1 millims. The flame em- 



