THE BAROMETER. 



THE BAROMETER. 



IM the history of human discovery, there are few more impressive lessons 

 of humility than that which is to be collected from the records of the progress 

 by which the pressure of the atmosphere which surrounds us, and the manner 

 in which it is instrumental in producing some most ordinary phenomena, 

 became known. Looking back from the point to which we have now attained, 

 and observing the numerous and obvious indication? of this effect which pre- 

 sent themselves at all times, and on all occasions, nature seems almost to have 

 courted the philosopher to the discovery. With every allowance for the feeble- 

 ness of the human understanding, and for the disadvantages which the ancients 

 labored under, as compared with more recent investigators, still one is inclined to 

 attribute the lateness of the discovery of the atmospheric pressure and its effects, 

 not altogether to the weakness and inadequacy of the mental powers applied 

 to the investigation. There seems to be something of wilful perverseness and 

 obstinacy instigating men to step aside from that course, and to turn their minds 

 from those instances which nature herself continually forces upon them. 



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 sur- 

 rounding 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. One end of a tube being 

 immersed in a liquid, and the other placed between the lips, the air was drawn 

 from the tube by the ordinary process of inhaling ; the water was immediately 

 observed to fill the tube as the air retreated. This phenomenon was accounted 

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

 pelled the water to fill the space deserted by the air. 



