THE ATMOSPHERE. 



Barometer is an instrument for measuring the 

 weight of the atmosphere ; it was invented in 1643 by 

 Torricelli, who in investigating the cause of water as- 

 cending in pumps to the height of 32 feet, and no higher, 

 made the following experiment. He took a glass tube 

 about four feet long, sealed at one end and open at the 

 other, and having filled it with mercury closed the open 

 end with his finger; he then inverted the tube, and 

 placed the open end under the surface of a small quan- 

 tity of mercury in a bason, and raising the tube perpen- 

 dicular withdrew his finger ; he observed the mercury 

 in the tube suspended to the height of 27 \ inches, 

 above the surface of that in the bason : he compared 

 the height of the column of mercury with the height of 

 the column of water raised by the pump, and perceiving 

 those heights to be in an inverse ratio of the specific 

 gravities of the water and mercury, he concluded they 

 were kept in suspension by a common cause ; a further 

 consideration of the experiment led him to remark that 



