Intelligence and Miscellaneous Articles. 395 



metres long could constantly be brought to a white heat. Doubtless 

 these are very vague indications for estimating the temperature and 

 the intensity of the current ; but they suffice to give an idea of the 

 conditions of the experiment. 



The thermoheliorneter being placed on a level with the carbons, 

 and the blackened thermometer at a distance of 395 millims., there 

 was found, at the end of half an hour, a difference of 3°-63 between 

 the temperature of the other thermometers and that of the black- 

 bulb ; this difference remained constant for an hour, the fluctua- 

 tions being insignificant. 



The temperature produced by solar radiation was determined 

 about noon on several days in July, and with the same instrument. 

 For the difference there was found 17°' 16, a quantity which agrees 

 very well with that which was obtained several years since. To 

 this value, however, must be applied the correction due to the ab- 

 sorption produced by our atmosphere; taking into account the 

 height of the sun at the time of the observation, we are led to the 

 value 17°-37. 



Substituting these values in the preceding formula and calcula- 

 ting the diameters a and 5 from the dimensions and distances of the 

 radiant areas, we get 



I,=I e X 36-468; 



so that the solar radiation would be thirty- six and a half times that 

 of the carbons. Nevertheless this valuation is below the truth ; 

 for we know that the correction made for the absorption by the 

 atmosphere is too small. M. Soret found directly, on Mont Blanc, 

 21°-13 ; probably the value at the upper limit of our atmosphere 

 would be about 27°. These two values would give respectively — 



21°-13 I 5 =I C X 44-36, 



27° I,=I c x 56-66. 



These ratios differ considerably from those which have been given 

 by other observers. In the fear that there might be some cause of 

 enormous error in my electric light, I compared it with the light 

 of a stearine taper ; I found that it was equal to 1450 tapers of 

 commerce; it possessed therefore quite the intensity ordinarily 

 exhibited by a good pile. In another series of experiments, made 

 after the pile had been worked for some time, I found I«=I C X 47-5, 

 a result not very far from that at which I arrived above with the 

 temperature 21°- 13 obtained directly by M. Soret. 



Adhering, then, to this temperature of 21°- 13, which is incon- 

 testable and certainly less than the reality, and supposing that the 

 temperature of the radiating surface of the carbons is 3000° (a 

 number which is not exaggerated, since the whole extent of the 

 platinum submitted to the experiment was fused), and supposing 

 the radiation proportional to the temperature, we obtain for the 

 potential temperature of the sun 133780°, This value may even 



