THE UNIVERSE. DISCOVERIES IX THE CELESTIAL SPACES. 337 



elevation, were soon associated others respecting the varia 

 tions of pressure, and of the quantity of vapour in the 

 atmosphere ; as well as respecting the often observed 

 periodical succession of the winds, or the " law of rotation"' 

 of the wind. Galileo's just views of atmospheric; pressure 

 conducted Torricelli, a year after the death of his great 

 teacher, to the construction of the barometer. That the 

 column of mercury in the Torricellian tube stood higher 

 at the foot of a tower or of a hill, than on its summit, would 

 appear to have been first remarked at Pisa, by Claudio 

 Beriguardi; ( 5l9 ) and was observed 11 7e years later in 

 Erance by Perrier, who, at the request of his brother-in-law, 

 Pascal, ascended the Puy de Dome, a mountain 840 French 

 feet higher than Yesuvius. The idea of employing the 

 barometer for the measurement of heights now presented 

 itself readily ; it may possibly have been first awakened in 

 Pascal's mind by a letter from Descartes. ( 52 ) It is 

 unnecessary to explain at length all that the barometer 

 employed as a hypsometric instrument for the determination 

 of differences of elevation upon the surface of the earth, and 

 as a meterological instrument for investigating the influence 

 of currents of air, has contributed to the extension of 

 physical geography and meteorological knowledge. The 

 foundations of the theory of the currents of the atmosphere 

 were laid before the close of the 17th century. Bacon in 

 1644, in his celebrated " Historia naturalis et experimentalis 

 de ventis," ( 521 ) had the merit of considering the direction 

 of winds in connection with temperature and aqueous 

 precipitations ; but unmathematically denying the truth of 

 the Copernican system, he reasoned on the possibility "that 



