12 VARIATION OF TEMPERATURE 



The 7/iki/i temperature of these places for seventeen years (so far as reported) ending 

 witli 1842, was 46°. 49; bul the relative temperature of differenl sections of the Stale, 

 while it depends chieflj on the latitude* and elevation, is modified in some degree also l>\ 

 .i \.inet\ of other circumstances, such as the situation in regard to the sea, or othei Large 

 bodies of water, l *• • 1 1 » as u respects proximitj and direction ; the configuration of the sur- 

 . whether level or hilly, and the position and Blope of the lulls; the nature of the 

 sofl, and the extent of cultivation in the surrounding country. And before proceeding 

 farther, il becomes necessary to investigate briefly the laws by which we shall be guided in 

 relation to the three main circumstances mentioned above; so that having made a proper 

 allowance for these, we may see more clearly the effect of the Others. 



Thai the temperature of the air diminishes as we ascend, is a fact familiar to every one ; 

 hut the rale of decrease, especially where the slope of the country is gradual, is by no 

 means BO well ascertained. The experiment was tried at Paris by Gay-Lussac, who rose 

 in a balloon to the height of nearly -2.'!. mm feel, and found the difference in temperature 



to amount to 1° for ever] 316 feel of ascent. The mean of two other similar experiments', 



tried one at the same place and the other at Rode/ in the southern part of Fiance, each 

 at a height of a lntle less than 12, (tni) feci, showed a decrease m temperature of 1 ' in 400 

 feet. Mi. ('. F. Duranl has kindly furnished me with quite a number of observations of 

 the same kind, taken by him in seven differenl ascensions in a balloon, from New-York, 

 Albany, Baltimore and Boston, in the years 1831, 3 ami 4. The height at which they 

 wire taken varied from 1500 to S000 feet. Taking twenty of his observations, which are 

 capable of being arranged for comparison in twelve pairs, I find the decrease of tempera- 

 ture io be 1 in 425 feet. If, however, we reject the comparison of two pairs of observa- 

 tions, which show great discrepancies from the rest, and which appear by the circumstances 

 in which thej were taken to hi' entitled to less confidence, the result is 1° to every 370 

 feet of elevation. 



n numerous observations made bj Humboldt among the Andes and Cordilleras, he 



deduced the rate to be as follows, viz: For the first 1000 French metres = 3281 feet, 1° 

 for every 319 feet ; for the second, 1° in 538 feet ; for the third, 1° in 443 feet ; for (he 

 fourth, 1° in 250 feel ; for the fifth, 1 3 in 331 feet : and for the whole on an average, 1° 

 m 361 feet. In a single observation taken on Chimborazo at the height of about 19,300 

 feci, the difference in temperature was 1° in 399 feet. The mean of six pairs of simulta- 

 neous observations on the Alps and the plains below, showed a diminution of 1° in 262 

 ■ : "tie on the Peak of Tenei ilfe and at Orotava below, Bhowed 1° in 412 feet; one 

 on Mount Etna and at Catania, 1° in 312 feet ; the mean of twenty-one on the Pyrenees 

 and at places below, 1° in 305 feel ; the mean of seven taken at Clermont in France and 

 on elevations in its vicinity, 1° in 267 feet. Twenty-eight simultaneous observations have 



Til recent writers reject latitude as one of the elements of temperature, but, as it seems to me, anphilo- 

 •ophicalljr. 



