MELIiONI ON THE NOCTURNAL COOLING OF BODIES. 549 



the air ; so that this must remain in a state of almost absokite 

 rest some time after the setting of the sun. The soil of the 

 desert being moreover composed of dry, sandy earths, of bad 

 conducting quahty, can receive from the interior but a very poor 

 compensation 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. 



Another phenomenon resulting from the combination of the 

 two frigorific actions successively excited in the radiating body 

 and the medium which envelopes it, is the congelation 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 surrounded by a border of earth, 4 or 5 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 

 4 or 5 feet, marks 5° or 6° above zero; which leads to the im- 

 mediate inference, that the water lowers gradually its tempera- 

 ture down to the zero of the therm ometric scale (Centigrade) 

 by means of a series of actions and reactions perfectly similar 

 to those which produce, under the same circumstances of 

 calm and clearness of sky, the nocturnal cooling of any other 

 radiating matter exposed 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 thermometer 

 marks several degrees higher than the freezing-point. 



[Note of the Editors of the A/males de Chemie et de Physique.l 

 We suppress the third and last part of the Memoir, which is 

 devoted to the refutation of the hypothesis which ascribes the 



