53 



on the Globe, whether we go from the equator 

 to the poles, ascend from the surface of the earth 

 into the highest regions of the air, or dive into 

 the depth of the ocean. It is so much the more 

 interesting to compare the rapidity of this three- 

 fold decrement, as this phenomenon has a great 

 influence on the climatic distributions of vege- 

 table and animal productions. The mean tem- 

 perature of the lower strata of the air, which 

 corresponds to the sixty-fifth, forty-eighth, and 

 twentieth, degrees of north latitude, are, accord- 

 ing to the most recent observations, 0*5°, 10*7°, 

 and 25° ; whence it results, that a centigrade 

 degree corresponds nearly to a change of lati- 

 tude of 1° 45'*. Now the decrement of caloric 

 is one degree every ninety toises, when we raise 

 ourselves perpendicularly into the atmospheref. 

 It therefore follows, t hat under the tropics, where 

 the lowering of the temperature is very regular 

 on mountains of considerable height, 500 toises 

 of vertical elevation correspond to a change of 

 latitude of 9° 45'. This result, conformable 



* In England and in Scotland it is reckoned, that a degree 

 of Fahrenheit's thermometer corresponds to one degree of 

 latitude. Phil. Trans. 1775, vol. Ixxv, page 459. Thomson, 

 Hist, of the Royal Soc. 1812, p. 508. 



f Mr. d'Aubuisson finds only eighty-three toises to a degree 

 for Europe in summer at eight in the morning, consequently 

 at the period he thinks the most favourable. Journal de Phys. 

 t. lxxi, p. 38. For the torrid zone, see Observ. Astron. t. i, 

 p. 129. 



