78 Intelligence and Miscellaneous Articles. 



4. Like the soft iron, the condenser has developed heat increasing 

 to a fixed limit : like it it gradually loses this heat while t increases ; 

 it is again Joule's law : 



T//2 



C"'= — , 

 a 



putting 



r Pa 



Q + * 



The condenser behaves like a resistance equal to unity traversed 

 by a current of the mean intensity I" which follows Ohm's law. We 

 assume that I" is the mean intensity of the extra current. — Comptes 

 Rendus, August 16, 1S69. 



ON THE CALORIFIC POWER OF THE LUNAR RAYS. 

 BY M. H. MARIE-DAVY. 



Older experiments made by concentrating, through the aid of 

 mirrors or of lenses, the light of the moon on the most delicate ther- 

 mometers, gave no appreciable result. Melloni was the first to ob- 

 serve any heating, by concentrating the lunar rays on the face of 

 the pile by means of a glass lens of 3 feet aperture. 



Mr. Piazzi Smyth, in the scientific expedition which he undertook 

 in 1856 to the Peak of Teneriffe, confirmed Melloni's experiments. 

 Piazzi Smyth collected the rays directly on the pile, the face of 

 which was provided with the ordinary cone of polished metal. 

 Although the moon was very low, the effect of its rays was a third of 

 that of the rays of a wax candle placed at a distance of 4*75 metres from 

 the pile. A candle placed at the same distance from my pile gave 

 a deflection of 17°"3 without the introduction of the cone. The 

 direct rays of the moon would therefore have produced a deflection 

 of 5 0, 8, corresponding to o, 00075, if it is possible to compare the 

 flames of candles at such long intervals of time and place. 



Lord Rosse, working with a reflector of 3 feet aperture, obtained 

 still more marked results. His thermopile had been previously gra- 

 duated by being exposed in front of blackened surfaces at definite 

 temperatures. Lord Rosse concludes from his results that the 

 moon's heat-radiation equals that of a surface heated to 182° C. 



In a Note, of February 18, 1869, on the Heat received from the 

 Stars by the Earth, Mr. Huggins, while establishing the fact of heat 

 from the stars Sirius, Pollux, Regulus, Arcturus, announces that 

 his observations on the full moon were not concordant. On one 

 night a sensible effect was produced ; on others, the indications were 

 excessively feeble and were not uniform enough to warrant any con- 

 fidence being placed in them. Mr. Huggins worked with a refractor 

 of 8 inches, the lenses of which stop almost entirely the obscure 

 heat-rays of the moon, while Lord Rosse's reflector reflects them like 

 the luminous rays. 



The moon sends us three kinds of heat-rays — the luminous and ob- 

 scure rays of the sun reflected or diffused by it, and the rays emanating 



