288 PHILOSOPHY OF STORMS. 



on the temperature at all, as it swims on the top of the 

 atmosphere; but in this he would be wrong, for it would 

 increase the temperature at the surface of the earth by its 

 radiation. The efflux of air above, from the borders of a 

 great storm-cloud, often produces an increase of tempera- 

 ture below by 'radiation, before the storm comes upon us, or 

 any southern wind. It is a prevailing idea, that air does 

 not radiate caloric. But this cannot be true; for it is the 

 upper regions of the air, or at least a considerable distance 

 above the surface of the earth, where the latent caloric of 

 vapor is given out in the formation of clouds ; a quantity 

 sufficient, in many countries where sixty or eighty inches 

 of rain fall, to heat it in one year six or eight hundred de- 

 grees. All this it must gradually part with, by radiation, 

 after each successive rain. 



It may, perhaps, be objected, that as the upper regions of 

 the air, even in their warmest state, are much colder than 

 the lower, they can never be said to warm the lower regions 

 by their radiation ; but this objection will vanish when we 

 consider that the surface of the earth would become much 

 colder in a given time by radiation, if it received no heat 

 from the upper regions of the atmosphere, and from the ce- 

 lestial vault in the evening, when the sun's rays are with- 

 drawn. M. Pouillet has made a most ingenious attempt by 

 means of an Actionometer of his own invention, to ascertain 

 approximately, the quantity of heat which is radiated from 

 the upper regions of the air to the surface of the earth, and 

 also, the quantity which is radiated from the fixed stars; 

 and if his experiments do not settle the question, they at 

 least prove, that the quantity of caloric, reaching the earth 

 from those two sources is not inconsiderable, and also, that 

 the upper regions of the air cool many degrees during the 

 night, when they are receiving no heat from the sun. A wide 

 field of investigation is here laid open to the future meteoro- 

 logist ; and I would recommend to every one who shall un- 



