TEMPERATURE. 



ference between tlie temperature of different feafons of the 

 year. The following table exhibits the temperature between 

 the hotteft and coldeft months, in different latitudes. 



Cumana ... 

 Vera Cruz, 

 Havannah 



Natches ... 



Philadelphia 



Quebec ... 



Nain ... 



In the temperate zone, as we advance northwards, the 

 coldnefs of the winter increafcs at a much greater rate than 

 the heat of the fumnier diminilhes. Thus at Enonlekis, in 

 latitude 68° 30', the temperature of July is as hot as that 

 of Edinburgh. Between the tropics, the temperature at no 

 feafon of the year equals that of the fea-diore ; but in tile 

 temperate zone, the upper currents of air are fomctimes 

 warmer than the lower, during the winter months ; and the 

 thermometer, on the fnmmits of hills, is occafionally three or 

 four degrees higher than in the plains. Hence in the tem- 

 perate zone, we find the fame plants frequently on low and 

 elevated fituations ; but tliis is never the cafe between the 

 tropics. In the temperate zone on the old continent, when 



the mean heat of the motitli is as under, the following 

 plants bloffom : 



Fiilir. 



42°, the Amygdalis perfica, 

 47, the Prunus doniellica, 

 52, the Betula alba. 



The reafon why plants vegetate with greater rapidity in 



Lapland and Norway than farther foutli, is owing to the 

 increment of temperature being mucli greater, and to thp 

 temperature of the earth in winter being feveral degrees 

 above that of the air. 



From obfervations made in different latitudes, it appears 

 that 1000 fathoms of altitude occaiion a diminution of tem- 

 perature equal to 23° of Fahrenheit ; 50 fatlioms being 

 nearly equal to half a degree. Mountains 1000 fathoms in 

 height, at 46° of latitude, liave the mean temperature of 

 Lapland ; and mountains of the fame lieight between the 

 tropics enjoy the temperature of Sicily. 



The following table by Humboldt exhibits the moil re. 

 markable circumilances refpecting tlie temperature in the 

 three zones. The temperature is taken according to the 

 centigrade thermometer. The fathom 6 French feet, or 

 6.39453 Englilh feet. 



In the feventh volume of the Tranfaftions of the Royal 

 Society of Edinburgh, Dr. John Murray has pubhfhed a 

 paper on the diffufion of heat on the furface of the earth ; in 

 ■which he attempts to prove, from the nature of caloric, that 

 the temperature of the earth is conftantly increafing from the 

 folar rays, and that this temperature is becoming more equal 

 in different parts of the earth. The atmofphere, he con- 

 tends, conveys no heat into unlimited fpace ; our pl.inet, in 

 relation to the difcharge of caloric from it, is bounded as it 

 were by a wall of iron-conduAing matter. He adroit?, 



however, that a fmall portion of heat may be loft by radia- 

 tion : thus, at the liotter parts of the earth's furface, there 

 may be fome emiffion of caloric by radiation ; but this, he 

 fays, cannot be equal to the quantity communicated by the 

 folar rays : for of the heat derived from the latter fourcc, a 

 portion is abforbed by the earth, and conveyed to the in- 

 terior, as is apparent from the decreafing temperature, as 

 we recede from the furface to a certain depth ; and another 

 portion is carried off by the afcending current of heated air, 

 and conveyed to cglder regions, where it is abforbed. Tiius, 



evcB 



