the coritrj 



EXPERIMENTS ON MAEIOTTE'S LAW. 



241 



contrivance for sliding 

 and clamping b along the 

 scale is not shown in the 

 figure, in order to avoid con- 

 fusion. The india-rubber 

 tube and part of the glass 

 tubes are filled with mer- 

 cury. To begin the experi- 

 ments the stop-cock of a is 

 opened, and b is clamped so 

 that the top of the column 

 in both tubes is opposite 

 to the same division o the 

 ! scale, for example at 90 cm ', as 

 in fig. 166 A. Both tubes 

 being now open, the atmo- 

 sphere presses equally upon- 

 the mercury in them, and let 

 this pressure be 74 cm at the- 

 time of the experiment, thotfr 

 is. let a column of mercuary 

 74 cm high counterbalance 

 the pressure of the- atmo- 

 >phere at that time. If now 

 the stopcock of the- tube a>. 

 'he closed, there remains in* 

 the tube, at the top of , the 

 mercury, a column of air- 

 (represented in the figure- a& 

 long, viz. reaching 

 from 90 to 100? m of the 

 scale); this column is still 

 under the pressure of the 



< 



FIG. 166 (i re al size). 



