149 



station 520 toises, supposing * the mean tempe- 

 rature of the coast to be 21°, and allowing one 

 degree for the decrement of caloric correspond- 

 ing under this zone to 93 toises. We should 

 not be surprised, if this spring remained a little 

 below the heat of the air, since it is probably 

 formed in some more elevated part of the peak, 

 and communicates perhaps even with the small 

 subterranean glaciers, of which we shall speak 

 hereafter. The accordance which we have just 

 observed between the barometrical and thermo- 

 metrical measures is so much the more striking 

 because in general, as I have elsewhere explain- 

 ed f, in mountainous countries, with steep de- 



* As a proof that these objections are founded on accurate 

 observations, [ will here observe, that the mean temperature 

 of the low regions of the isle of Madeira, which is a little to 

 the north of TenerifFe, is 20*4° ; and that my observations, 

 made under the torrid zone, allow for the decrement of caloric 

 98 toises to each centesimal degree ; while the results taken 

 by Mr. Ramond, under the temperate zone^ in latitude 45°, 

 give 84 toises. From these extremes it follows, that the 

 height of the Dornajito is either 548 toises, or 470 toises. 

 Mr. de Borda found in 1776 the temperature of the air near 

 the spring 5° colder than at. the port of Orotava, which seems 

 to prove, that the decrement of 93 toises, which I have sup- 

 posed, is not too slow. Phil. Trans, vol. xlvii, p. 358. .Ra- 

 mond, Mem. sur la Formula barom. p. 189. 



+ Astron. Obs., vol. i, p. 132. Thus in the Blue Mountains 

 of Jamaica Mr. Hunter found springs constantly colder than 

 they ought to have been, according to the height at which they 

 issued. 



