MEASUREMENTS 



313 



FIG. 221. Two automatic spirometers coupled together (on the left is 

 a eudiometer for analysis.) 



hollow metal tubes to increase the displacement of the water. It 

 is suspended within a receptacle K, of which the annular part is 

 filled with water. A tube, G, leads in the expired gases. The 

 bell rises, and is exactly balanced in every position by an auto- 

 matic counterweight. The bell is suspended by a thin steel wire, 

 which passes over an aluminium pulley, with practically no fric- 

 tion, and carries a counterweight, consisting of a cylindrical glass 

 tube, V, closed at the bottom and having a section exactly equal 

 to that of the hollow tubes of the bell, to which is suspended a 

 receptacle P, full of lead shot. A syphon tube, S, connects K 

 with the tube V. As soon as the syphon is started, a rise of the 

 bell will produce an equal lowering in the tube V, and the water 



