IS METEOROLOGY. 



already existing cloud dissolved, and the formation of other prevented. 



If we regard the preceding explanation as correct, the greater degree 

 of cold generally prevailing at that time must be referred to the effect of 

 the free radiation of the heat of the earth through an almost perfectly 

 transparent sky. When the sky is obscured by clouds or vapors the 

 heat radiated from the earth is arrested by them and returned so that its 

 surface receives nearly as much as it rejects, and the temperature re- 

 mains almost stationary. On the contrary, when the sky is clear, the 

 radiant heat passes off into the depths of space and cold is produced. 



But whilst it is admitted that this is a very ingenious and plausible 

 explanation of the phenomena in question, it seems like attributing en- 

 tirely too much to lunar radiation. A temperature like that of boiling 

 water, or even one far greater, must, according to the law of all emana- 

 tions, which is, that they diminish as the squares of the distance from 

 the source increase, yield a quantity of heat at the distance of the earth's 

 atmosphere, far too small to be appreciable, and consequently cannot be 

 adequate to the production of so striking a meterological phenomenon. 



As the preceding explanation is not perfectly satisfactory, the follow- 

 ing, which is however also not without its difficulties, is respectfully 

 suggested. With how much favor it may meet, it is at present difficult 

 to tell. 



The sun and moon both raise atmospheric tides, following them in 

 their diurnal course as do those of the ocean. When these bodies are 

 in conjunction, that is, in the same line with the earth, the tides they 

 raise in the ocean are the highest possible. The same may be inferred 

 to be the case in the atmosphere. At the time of full moon therefore, 

 the greatest possible atmospheric tide is produced, there being then a 

 determination of the colder air of higher latitudes to accumulate under 

 the moon's track. Now it is an established law of meteorology that 

 such air having its temperature raised by coming into lower latitudes 

 will have its solvent power increased, and not only hold its own vapor 

 in perfect solution, but also dissolve that which it may meet in its pro- 

 gress, and thus a clear sky would be produced. It is not necessary to 

 suppose that there should be such a rapid approach of the air from 

 higiier latitudes as to produce considerable winds, but only a greater de- 

 termination than at other times. On the contrary, whenever there is an 

 accumulation above the mean, however small the exces^ may be, it is 

 accompanied with a perfect calm. 



The greater amount of cold then prevailing may be attributable in 

 part to the cause assigned under the theory above named, and in pait to 

 the afflux of air of lower temperature from higher latitudes. 



