M. Melloni on Dew. 371 



pensation in exchange for the heat it has lost. The solid 

 body radiating by night towards space, and the surrounding 

 medium, will therefore be unmoving and isolated, and thus 

 be in highly favourable conditions for reacting with energy 

 on each other, and considerably lowering their temperature. 



Artificial Freezing of Water in Bengal. 



Another phenomenon resulting from the combination of 

 the two frigorific actions, successively excited in the radiat- 

 ing body, and the medium which envelopes it, is the congela- 

 tion of water, produced artificially in Bengal, during the 

 calm and clear nights. It would be superfluous to repeat 

 here the details relative to this process, a description of 

 which may be found in all treatises on physics. It will be 

 sufficient to call to mind, that the vessels, very shallow and 

 uncovered, containing the liquid to be frozen, are placed at 

 the bottom of certain excavations made in the soil, and sur- 

 rounded by a border of earth, four or five inches in height ; 

 that the water, whose emissive power is nearly equal to that 

 of the leaves of plants, and of lamp black, does not descend 

 even two degrees lower than a covered thermometer placed 

 by its side, and that frequently the ice is formed when the 

 thermometer, elevated four or five feet, marks 5° or 6° above 

 zero ; which leads to the immediate inference, that the water 

 lowers gradually its temperature down to the zero of the 

 thermometric scale (centigrade), by means of a series of ac- 

 tions and reactions, perfectly similar to those which pro- 

 duce, under the same circumstances of calm and clearness of 

 sky, the nocturnal cooling of any other radiating matter ex- 

 posed to the free air, and the decrease of the atmospheric- 

 temperature, in proportion as we approach the earth's surface. 



It is in consequence of these same frigorific actions that 

 the buds of plants, and the shallow waters of ditches and 

 ponds, scattered here and there over the country, often freeze 

 during the calm and clear nights of spring, whilst the ther- 

 mometer marks several degrees higher than the freezing 

 point. — {Extracted from MellonVs Memoir on Dew. — Uicliard 

 Taylor's, Esq., F.8.A. Sc, Scientific Memoirs, Vol. v., Part 

 xx. April 1852, p. 543.) 



