640 COSMOS 



/ect view was taken up by Halley late in the eighteentii 

 century, and was then more fully and satisfactorily explained 

 with reference to the action of the velocity of rotation pe- 

 culiar to each parallel of latitude. Halley, prompted by his 

 long sojourn in the torrid zone, had even earlier (1686) pub- 

 lished an admirable empirical work on the geographical ex- 

 tension of trade winds and monsoons. It is surprising that 

 he should not have noticed, in his magnetic expeditions, the 

 law of rotation of the winds, which is so important for the 

 whole of meteorology, since its general features had been rec- 

 ognized by Bacon and Johann Christian Sturm, of Hippol- 

 stein (according to Brewster, the actual discoverer of the 

 differential thermometer*). 



In the brilliant epoch characterized by the foundation of 

 mathematical natural philosophy, experiments were not v/ant- 

 ing for determining the connection existing between the hu- 

 midity of the atmosphere, and the changes in the tempera- 

 ture and the direction of the winds. The Accademia del 

 Cimento had the felicitous idea of determining the quantity 

 of vapor by evaporation and precipitation. The oldest Flor- 

 entine hygrometer was accordingly a condensation-hygrome- 

 ter — an apparatus in which the quantity of the discharged 



avesse necessity d'obbedire al suo moto, se non in quanto 1' asprezza 

 della superficie teirestre ne rapisce, e seco porta una parte a se contigua, 

 che di non molto intervallo sopravauza le maggiori altezze delle nion- 

 tagne ; la qual pozzion d'aria tanto meiK> dovr^ esser renitente alia 

 conversion terrestre, quanto che ella h ripiena di vapori, fumi, ed esala- 

 zioni, materie tutte participanti delle qualita terrene : e per conseguen- 

 za atte nate per lor uatura (? ) a i medesimi raovimenti. Ma dove, man- 

 cassero le cause del moto, cioe dovala superficie del globo avesse grandi 

 spazii piani, e meno vi fusse della mistione de i vapori terreni, quivi ces- 

 serebbe in parte la causa, per la quale 1' aria ambiente dovesse total- 

 mente obbedire al i-apimento della conversion terrestre ; si che in tali 

 uoghi, mentre che la terra si volge verso Oriente, si dovrebbe sentir con- 

 tinuamente un vento. che si ferisse, spirando da Levante verso Ponente; 

 e tale spiramento dovrebbe farsi piu sensibile, dove la vertigine del 

 globo fusse piu veloce : il che sarebbe ne i luoghi piu remoti da i Poli, 

 e vicini al cerchio massinio della diurna conversione. L'esperienza ap- 

 plaude molto a questo filosofico discorso,poich^ ne gli ampi mari sotto- 

 posti alia Zona torrida, dove anco I'evaporazioni terresti'i raancano (?) 



si sente una perpetua aura muovere da Oriente " 



* Brewster, in the Edinburgh Journal of Science, vol. ii., 1825, p. 145. 

 Sturm has described the Differential Thermometer in a little vt^ork, en- 

 titled Collegium Experimentale Curiosum (Nuremberg, 1676), p. 49. 

 On the Baconian lav^r of the rotation of the wind, which was first ex- 

 tended to both zones, and recognized in its ultimate connection with 

 the causes of all atmospheric currents by Dove, see the detailed treatise 

 of Muncke, in the new edition of Gehler's Physikal. Worterbuch, bd 

 X., 8. 2003-2019 and 2030-2035. 



