100 Baron Von Buch's Observations 



The mean of these is •28. ^'".791, or adding, for 30 feet above 

 the sea, 28 inches 3'".09 lines. 



This is very considerable, and is fully confirmed by the obser- 

 vations of Don Francisco Escolar, at Santa Cruz. The mean of 

 the extremes, for three years, reduced to the freezing point, and 

 to the level of the sea, is 28 inches 2'". 441 lines. And if these 

 monthly extremes be not fallacious, the pressure of the air in 

 summer, when the north-east and westerly winds are placed above 

 each, appears, in fact, to be greater than in the winter months, 

 when the south-west alone prevails. For the mean of the four 

 months. May, June, July and August, is 28 inches 3.173 lines. 

 The mean height from September to April 28, 2.017 ; the diffe- 

 rence of which is 1.156 lines. 



How very different is this from the state of the barometer in 

 countries at the equator ! How very different from what it is 

 found to be in England, Ireland and Norway ! Seven days^ ob- 

 servations in May, at Puerto Orotava, gave the height of the 

 barometer, at the level of the sea, at 28°1.79. Seven days' ob- 

 servations at the same place, in September and October, gave 

 28°2.38. And, lastly, three days' at Lancerote, 28°3.8. 



When to this is added, that the naturalists who have ascend- 

 ed the Peak with barometers, have never marked them low at 

 the level of the sea, Lamanon 28°.3'", at Santa Cruz, Cordier 

 even 28 inches, 5^^^. 6 at Puerto Orotava, on the 17th of April, 

 (Journal de Physique, Ivii. 57.), a somewhat greater height of 

 the atmosphere, over these islands, becomes almost probable. 



When the west wind of the upper regions descends obliquely 

 in avitumn, and thereby reaches the surface sooner in northern 

 than in more southern parts, it must, long before it reach the 

 latter, have completely interrupted the course of the north wind ; 

 and hence it is, that, at this season, places particularly exposed 

 to the trade wind are left in a perfect calm. Is the course of 

 local winds prevented by the nature of the environs ? The heat 

 being no longer carried off, will increase considerably, till again 

 reduced, by regular winds. In this way I would explain the 

 very singular, and, as I believe, unprecedented phenomenon, 

 that at Las Palmas in Grand Canary, the greatest heat does not 

 occur in July or August, but in the middle of October ; and so 

 singular is it, that, till September, the heat, as compared witli 



