12 VARIATION OF TEMPERATURE 



The mean tpinpcratnro of these places for seventeen years (so far as reported) ending 

 with 1842, was 46°. 49; but the relative temperature of different sections of the State, 

 while it depends chiefly on the latitude* and elevation, is modified in some degree also by 

 a variety of other circmnstances, such as the situation in regard to the sea, or other large 

 bodies of water, both as it respects proximity and direction ; the configuration of the sur- 

 face, whether level or hilly, and the position and slope of the hills; the nature of the 

 soil, aiul I lie extent of cultivation in the surrounding country. And before proceeding 

 farther, it becomes necessary to investigate briefly tlie 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. 



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

 but the rate of decrease, especially where the slope of the country is gradual, is by no 

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

 in a balloon to tlic height of nearly 23,000 feet, and found the difference in temperature 

 to amount lo 1° for every 316 feet of ascent. The mean of two other similar experiments, 

 tried one at the same place and the other at Rodez in the southern part of France, each 

 at a height of a little less than 12,000 feet, showed a decrease in temperature of 1° in 400 

 feet. Mr. C. F. Durant has kindly furnished me with quite a number of observations of 

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

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

 were taken varied from 1500 to 8000 feet. Taking twenty of his observations, which are 

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

 ture to be l'^ 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 lliey were taken to be entitled to less confidence, the result is 1° to every 370 

 feet of elevation. 



From numerous observations made by 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 the 

 fourth, 1° in 250 feet; for the fifth, \^ in 331 feet; and for the whole on an average, 1° 

 in 351 feet. In a single observation taken on Chimborazo at the height of about 19,300 

 feet, the dif'-rence in temperatme 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 

 feet; one on the Peak of Teneriffe and at Orotava below, showed 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 feet; the mean of seven taken at Clermont in France and 

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



•Several recent writers reject latitude as one of the elements of temperature, but, as it seems to me, unpliilo- 

 Bophically. 



