THE ATMOSPHERE. 5? 



not have sunk below the point marked Fair; and the 

 same may be noticed with regard to its rise. 



By this instrument we detect an error very common 

 among mankind, respecting the weight of the air. It 

 is generally supposed that air is heaviest when the atmo- 

 sphere is cloudy and filled with moisture, and that the 

 languor we then experience is produced by the increased 

 weight upon our bodies. But the reverse is the fact. 

 When the atmosphere is heavy, clouds do not linger 

 near the earth, smoke rises almost perpendicularly, and 

 we experience a peculiar elasticity and energy. When 

 it is light, on the contrary, clouds come very near the 

 earth, smoke falls immediately to the ground, and the 

 animal system feels languid and oppressed. The baro- 

 meter proves that the weight has been diminished; for 

 the quicksilver, not being counterbalanced by so heavy a 

 column of air, .necessarily sinks. Therefore, we find 

 that when the atmosphere is heaviest, our sensations 

 are most agreeable, and when it is lightest, the internal 

 pressure, not being fully resisted, produces the feelings 

 of languor and oppression. 



There are four forms of the barometer in use, each 

 of which presents certain advantages. 



1st. The portable, or parlor barometer. 



2d. The wheel barometer. 



3d. The marine barometer. 



4th. The mountain barometer. 



All these are modifications of the same principle. 

 The first is the simplest, and was described in explain- 

 ing the peculiarities of the instrument. It acquires the 

 name of portable from the screw which is connected 

 with the cup at the bottom, whereby the fluid can be 

 pressed up the whole length of the tube, to prevent ac- 

 cidents in its transportation. 



The second differs very much in appearance ; the 

 tube being concealed, and a face somewhat resem- 

 bling that of a clock, exhibiting the changes by the mo- 

 tion of a hand. 



The third differs from the first in having the bore of 

 the tube of unequal diameters, to guard against the 

 accidents by motion of the vessel. 



