WATER BAROMETER. 



the water in the reservoir; the other 14 feet of the tube remaining 

 empty. 



It followed, therefore, that the column of water, 34 feet high, 

 exactly balanced a corresponding column of air extending from 

 the surface to the top of the atmosphere. 



It appears, therefore, from the result of this celebrated experi- 

 ment, that every part of the surface of the globe, whether it be 

 land or water, and of the surface of every object upon the globe, 

 is subject to the same pressure as if it were at the bottom of a 

 reservoir of water 34 feet deep. 



8. When we look back upon the progress of physical discovery 

 during former ages in this department of knowledge, and consider 

 the numerous phenomena which were constantly offered by Nature 

 herself to the least attentive and the least acute, it cannot fail to 

 excite surprise, that the grosser and more obvious properties of 

 that universally diffused fluid which everywhere surrounds us, and 

 of which mankind in every age and country have so largely availed 

 themselves for the uses of life, should remain not only undiscovered 

 but altogether misapprehended. Even those who claimed the 

 rank and title of philosophers seemed to have turned aside from 

 the plain path of discovery pointed at by the finger of Nature, and 

 with a perverseness and fatal obstinacy devoted their faculties to 

 the invention of fanciful theories and hypotheses, having so little 

 analogy to truth or nature, that the bare statement of them now 

 seems grotesque. 



The ancient philosophers observed, that in the instances which 

 commonly fell under their notice space was always filled by a 

 material substance. The moment a solid or a liquid was by any 

 means removed, immediately the surrounding air rushed in and 

 filled the place which it deserted : hence they adopted the physical 

 dogma that Nature abhors a vacuum. Such a proposition must be 

 regarded as a figurative or poetical expression of a supposed law 

 of physics, declaring it to be impossible that space could exist 

 unoccupied by matter. 



Probably one of the first ways in which the atmospheric pressure 

 presented itself was by the effect of suction with the mouth, above 

 described. This phenomenon was accounted for by declaring 

 that "nature abhorred a vacuum," and that she therefore com- 

 pelled the water to enter the tube and fill the space deserted by 

 the air. 



The effects of suction by the mouth led by a natural analogy- to 

 suction by artificial means. If a cylinder be open at both ends, 

 and a piston playing in it air-tight be moved to the lower end, 

 upon immersing this lower end in water, and then drawing up 

 the piston, an unoccupied space would remain between the piston 



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