76 Experimental Philosophy. [Lecture 6. 



of the water and the top of the vessel is then of 

 the same density with that of the atmosphere. 

 We then take the condensing syringe, fig. 32, 

 and screw it above the stop cock, and force a 

 quantity of air into the vessel, which, as it can- 

 not return, forces its way through the water into 

 the upper part of the fountain, where it remains 

 in a condensed state ; while the air in the foun- 

 tain or vessel is condensing, we turn the stop 

 cock R to prevent the escape of the water. We 

 then screw on a jet or pipe with a small aperture 

 at top, and when we turn the stop cock again, 

 the condensed air above, by its expansion, forces 

 the water through the pipe, and out at the jet, in 

 a beautiful fountain. 



The condensing syringe, fig. 32, is made like 

 a common squirt or syringe ; but it has a valve 

 at bottom, which, instead of opening inwards as 

 the valve of a pump, opens outwards at R. Near 

 the top of the syringe there is a small hole P. 

 When, therefore, the condensing syringe is 

 screwed on the vessel, if we draw up the piston 

 (which is solid, as in a squirt, and not with a 

 valve, like the piston of a pump) there will be a 

 vacuum left between that and the valve, till we 

 draw up the piston as far as the little hole P, near 

 the top. When it gets past the hole, the exter- 

 nal air will rush in and fill up the vacuum ; when 

 we push the piston down again, by which ac- 

 tion the valve below is opened, and the air 

 forced into the vessel the valve shuts, and re- 

 strains the air from returning. 



