

DISCOVERIES IN THE CELESTIAL SPACES. 339 



was first observed at Pisa by Claudio Beriguardi ;* and fivf 

 years later in France, at the suggestion of Pascal, by Perrier, 

 the brother-in-law of the latter, when he ascended the Puy de 

 Dome, which is nearly one thousand feet higher than Vesu- 

 vius. The idea of employing barometers for measuring eleva- 

 tions now presented itself readily ; it may, perhaps, have been 

 suggested to Pascal in a letter of Descartes. t It is not nec- 

 essary to enter into any especial explanation of the influence 

 exercised on the enlargement of physical geography and mete- 

 orology by the barometer when used as a hypsometrical instru- 

 ment in determining the local relations of the Earth's surface, 

 and as a meteorological instrument in ascertaining the influ- 

 ence of atmospheric currents. The theory of the atmospheric 

 currents already referred to was established on a solid foun- 

 dation before the close of the seventeenth century. Bacon 

 had the merit, in 1664, in his celebrated work entitled His- 

 toric!, Naturalis et Ezperimentalis de Ve?itis,t of considering 

 the direction of the winds in their dependence on thermometric 

 and hydrgmetric relations ; but, unmathematically denying the 

 correctness of the Copernican system, he conjectured the pos- 

 sibility " that our atmosphere may daily turn round the earth 

 like the heavens, and thus occasion the tropical east wind." 



Hooke's comprehensive genius here also diffused order and 

 light. He recognized the influence of the rotation of the 

 Earth, and the existence of the upper and lower currents of 

 warm and cold air, which pass from the equator to the poles, 

 and return from the poles to the equator. Galileo, in his last 

 Dialogo, had indeed also regarded the trade winds as the con- 

 sequence of the rotation of the Earth ; but he ascribed the 

 detention of the particles of air within the tropics (when com- 

 pared with the velocity of the Earth's rotation) to a vaporless 

 purity of the air in the tropical regions.ll Hooke's more cor- 



* Antinori, p. 29. 



t Ren. Cartesii Epistolce (Amstelod., 1682), Part iii., ep. 67. 



X Bacon's Works, by Shaw, 1733, vol. iii., p. 441. (See Cosmo*, vol 

 i., p. 315.) 



Hooke's Posthumous Works, p. 364. (Compare my Relat. Histo 

 riqne, t. i., p. 199.) Hooke, however, like Galileo, unhappily assumed 

 a difference in the velocity of the rotation of the Earth and of the atmos- 

 phere. See Posth. Works, p. 88 and 363. 



|| Although, according to Galileo's views, the detention of the parti 

 cles of air is one of the causes of the trade winds, yet his hypothesis 

 ought not to be confounded, as has recently been done, with that of 

 Hooke and Hadley. Galileo, in the Dialogo quarto (Opere, t. iv., p. 

 311), makes Salviati say, " Dicevamo pur' ora che' l'aria, come corpo 

 tenue, e fluido, e non saldamente congiunto alia terra, pareva che non 



