250 Mr Black on the Climate 



small quantity of rain that had yet fallen in Italy, not being 

 sufficient to cool the surface of the land ; while, on the other 

 hand, this hot and dry wind had acquired much humidity from 

 the sea, before it retrograded and was repelled by the succeed- 

 ing southerly currents. The Sirocco or SE. wind is an import- 

 ant one in any part of the Mediterranean ; and different opi- 

 nions have been formed as to its dryness and moisture. The 

 fact is, that these qualities are entirely governed by the surfaces 

 over which it blows, before reaching the place of observation. 

 Thus it is moist and warm, as felt on the coasts of Greece and 

 Italy; because its exalted temperature imbibes much vapour 

 from the sea, after it leaves the northern shores of Ati'ica, where 

 it is hot and dry. Nowhere can such a wind be felt in the inte- 

 rior or the northward of Europe ; for there is nowhere in Eu- 

 rope such a country as the Lybian and Arabian deserts, so flat, 

 so dry, and so little capable of imparting to its winds any thing- 

 like the electric condition of the land and atmosphere of other 

 countries *. 



Electricity. — This is a modifying element in the constitution 

 of every climate; and, though less appreciated than heat or hu- 

 midity, it no doubt performs a most important part in all at- 

 mospheric changes ; if it is not an essential agent in every modi- 

 fication of cloud, dew, and vapour. The influences of heat and 

 humidity are much more easily defined than those of electricity ; 

 which, though in constant operation, only enables us to draw 

 any satisfactory induction from its great and palpable phenome- 

 na. Evaporation was long thought to be a fertile source of elec- 

 tricity ; and Pouillet -f has lately proved this opinion to be well 

 founded, as well as that chemical and vegetable change is ac- 

 companied by electrical disturbance. 



• To shew the difterent directions of the winds at London, from those of 

 the Mediterranean, as registered in the Table, the average winds for the year, 

 at the metropolis, are here extracted from the British Almanac for 1828. The 

 difference between the northerly winds is very remarkable. 



N. 30i days. E. 254 S. 28| W. 70^ 



NE. 441 ' SE. 38 SW. 72| NW. 64| 



t M. Pouillet, in his Memoirs read before the Academy of Sciences, on 

 80th May and 4th July 1825, has shewn that the absorption of carbonic acid 

 by vegetables, and the evaporation of all liquids, pure or impure, are accom- 

 panied with the developement of electricity. 



