340 M. Humboldt (ni the Difference of the 



rapidly. This variety animates industry and the commercial 

 intercourse of nations. 



We may here state that partial, daily, and monthly changes 

 of temperature are, on account of the motion of the atmosphere, 

 produced by the transportation of colder or \^armer strata, by 

 greater or less electric tension, by the formation of clouds or the 

 diffusion of vapours ; in short, by an almost infinite number of va- 

 riable causes, acting at a greater or smaller distance. The study 

 of meteorology has, unfortunately, begun in a zone where the 

 causes are most comphcated, and the number and intensity of the 

 disturbing powers greatest. If ever civilization, as may now be 

 expected, shall establish one of its principal seats in the tropics, it 

 is to be presumed that these phenomena, which are so simple 

 there, will be more easily ascertained than in our climates, where 

 the play of many conflicting causes has so long concealed them 

 from our view. From that which is simple it is easy to proceed to 

 what is complicated, and we may imagine a scientific meteorolo- 

 gy as returning from the tropics to the north. In the climate 

 of palms, a feeble east wind always brings strata of air along 

 with it, having generally the same temperature. The barometer 

 shows, like the progress of the needle, the hour of the day. 

 Earthquakes, tempests, and thunder-storms do not disturb the 

 small but periodical tides of the atmosphere. The changed decli- 

 nation of the sun, together with the upper currents of the air, 

 from the equator towards the pole, modified by this declina- 

 tion, determine the beginning of the rainy season and the elec- 

 tric explosions, which both begin at regular periods. The tra- 

 veller may know his way almost as well by the direction of the 

 clouds as by the compass ; and, in the dry season, the appear- 

 ance of a cloud on the deep blue sky would, in many districts of 

 the tropics, astonish the natives as much as the fall of an aero- 

 lite or of the red polar snow would do us ; or as the crash of 

 thunder in Peru ; or, in the tropical plains, a hail storm. This 

 simplicity and regularity in the meteorological phenomena allow 

 us to expect an easier and more favourable insight into the re- 

 lation of their causes. 



As long as the observations on the magnetic inclination, de- 

 clination and intensity of forces, remained dispersed in the re- 

 ports of travellers, and had not been united by magnetical lines. 



