260 



APPLICATIONS OF MARIOTTE'S LAW. 



Mariettas Bottle, fig. 181 A, is a bottle with a 

 tubulure a for the insertion of the discharge-tube b\ 

 the neck of the bottle is closed by a tightly-fitting 

 cork, through which the tube c d passes air- 

 tight, but so that it may be moved up or down 

 without diificulty. When the lower end d of this tube 

 is higher than the mouth of the discharge-tube b, as is 

 represented in the figure, liquid flows from b while air 

 enters through c d. At d the liquid is in contact 

 with the external air and the pressure at that point is 

 equal to the atmospheric pressure; from d upwards 

 the pressure evidently decreases, but downwards it in- 



FIG. 181 (^ real size). 



creases, and at b it exceeds the external pressure by the i 

 pressure of a liquid column which has the height d I. 

 The difference of pressure, which causes the flow of the 

 liquid from &, is thus independent of the real height 

 of the liquid in the bottle ; it is the same as if the 



