366 



ATMOSPHERIC PRESSURE. 



Training 

 of previous 

 labours. 



Natural 

 uptitudi. 



CH.\PTKR searches in Central Asia," as well as in the previous pre- 

 ^ ^^ ^' ^' paratory work, the " Frat^inens Asiatiques." 



Hurabohlt had already been trained by his previous 

 labours, not onlj'^ as an observer and a collector of facts, 

 but still more, as a detector of those general laws by 

 which the numerous detached indications of such are 

 united into a consistent and harmonious whole. We 

 must not, however, overlook the no less important ele- 

 ment of success in the great natural gifts by which he is 

 so peculiarly fitted to become the scientific observer and 

 explorer. Training, and opportunities of observation, 

 were indispensable to him ; but without the natural apti- 

 tude for his important self-imposed duties, no amount of 

 preparatory trainint;, or means of observing, could have 

 fitted him for those remarkable generalizations by which 

 lie detected the operation of laws that govern the tem- 

 perature of the earth, the variations in its external form 

 and internal construction ; the disposition of its mine- 

 ral wealth ; the distribution of its living occupants, both 

 of the animal and vegetable kingdoms ; and the temper- 

 ature of the atmosphere, which exercises so great an 

 influence on most of these phenomena. 

 CUmatoiopy- On the general subject of climatology and atmospheric 

 jressure, Humboldt has thus expressed himself in his 

 later work : — " As the most important fluctuations of 

 the pressure of the atmosphere, whether occurring with 

 horary or annual regularity, or accidentally, and then 

 often attended by violence and danger, are, like all the 

 other phenomena of the weather, mainly owing to the 

 heating force of the sun's rays, it has long been sug- 

 gested that the direction of the wind should be com- 

 pared with the height of the barometer, alternations of 

 temperature, and the increase and decrease of humidity. 

 Tables of atmospheric pressure during different winds, 

 termed barometric windroses, afford a deeper insight into 

 the connection of meteorological phenomena. Dove has, 

 with admirai^le sagacity, recognised, in the 'law of rota- 

 tion' in both hemispheres, which he himself established. 



