230 DISCOURSE ON THE STUDY 



that if the weight of the incumbent air be the direct 

 cause of the elevation of the mercury, it must be 

 measured by the amount of that elevation, and there- 

 fore that, by carrying a barometer up a high mountain, 

 and so ascending into the atmosphere above a large 

 portion of the incumbent air, the pressure, as well 

 as the length of the column sustained by it, must be 

 diminished ; while, on the other hand, if the pheno- 

 menon were due to the cause originally assigned, no 

 difference could be expected to take place, whether 

 the observation were made on a mountain or on the 

 plain. Perhaps the decisive effect of the experiment 

 which he caused to be instituted for the purpose, on 

 the Puy de Dome, a high mountain in Auvergne, 

 while it convinced every one of the truth of Torri- 

 celli's views, tended more powerfully than any thing 

 which had previously been done in science to con- 

 firm, in the minds of men, that disposition to expe- 

 rimental verification which had scarcely yet taken 

 full and secure root. 



(247.) Immediately on this discovery followed 

 that of the air-pump, by Otto von Guericke of Mag- 

 deburgh, whose aim seems to have been to decide 

 the question, whether a vacuum could or could not 

 exist, by endeavouring to make one. The imper- 

 fection of his mechanism enabled him only to dimi- 

 nish the aerial contents of his receivers, not entirely 

 to empty them ; but the curious effects produced by 

 even a partial exhaustion of air speedily excited at- 

 tention, and induced our illustrious countryman, 

 Robert Boyle, to the prosecution of those experi- 

 ments which terminated in his hands, and in those 

 of Hauksbee, Hooke, Mariotte, and others, in a satis- 



