THE MOON'S LIGHT. 479 



May, 1848), Arago detected indubitable signs of polarization, 

 in the reddened disc of the Moon, the latter being a pheno- 

 menon of which we shall speak further on. ( Comptes rendus, 

 torn, xviii. p. 119.) 



That the moonlight is capable of producing heat is a dis- 

 covery which belongs, like so many others of my celebrated 

 friend Melloni, to the most important and surprising of our 

 century. After many fruitless attempts, from those of La 

 Hire to the sagacious Forbes, 20 Melloni was fortunate 

 enough to observe by means of a lens (lentillc a echellons} of 

 three feet in diameter, which was destined for the meteoro- 

 logical station on Vesuvius, the most satisfactory indications 

 of an elevation of temperature during different changes of 

 the Moon. Mosotti-Lavagna and Belli, professors of the 

 Universities of Pisa and Pavia, were witnesses of these ex- 

 periments, which gave results differing in proportion to the age 

 and altitude of the Moon. It had not at that time (Summer, 

 1848) been determined what the elevation of temperature 

 produced by Melloni's thermoscope, expressed in fractional 

 parts of the centigrade thermometer, amounted to. 21 



20 Forbes, On the Refraction and Polarization of Heat, in the 

 Transact, of the Royal Society of Edinburgh, vol. xiii. 1836, 

 p. 131. 



21 Lettre de M. Melloni a, M. Arago sur la puissance 

 calorifique de la lumiere de la Lune, in the Comptes rendus, 

 torn. xxii. 1846, pp. 541-544. Compare also on account of 

 the historical data the Jahresbericht der Physicalischen Gessell- 

 schaft zu Berlin, Bd. ii. p. 272. It had always appeared 

 sufficiently remarkable to me that from the earliest times, 

 when heat was determined only by the sense of feeling, the 

 Moon had first excited the idea that light and heat might be 

 separated. Among the Indians the Moon was called, in 

 Sanscrit, the King of the stars of cold (^sitala, hima\ also the 

 cold-radiating (hi'man'su}, while the Sun was called a creator 

 of heat (niddghakara). The spots upon the Moon, in which 



