216 ON DIVERGING STREAMS 



only one and 4-lOths of an inch of mercury ; but 

 the tube being brought over the seat at a distance 

 of 5-32nds from the edge of the aperture, shewed 

 a vacuum of one and 8-lOths of an inch of mer- 

 cury. From that point proceeding outward, the 

 vacuum became less. 



These experiments shewed, that until the valve 

 was raised to a certain height above its seat, the 

 under side of that part of the valve which was 

 over the aperture, was exposed to a pressure of 

 IJ inches of mercury more than atmospheric 

 pressure ; and the under side of all the rest of 

 the valve, forming an outer stripe or ring, was 

 exposed to a pressure less than atmospheric, or 

 had a partial vacuum varying from one and 

 8-lOths of an inch of mercury up to atmospheric 

 pressure. The superior pressure against the 

 under side of the center of the valve, must then 

 have been counterbalanced by the inferior pres- 

 sure against the under side of that part of 

 the valve which is nearer to the periphery, — and 

 more than counterbalanced, for atmospheric 

 pressure on the top of the valve was still so 

 superior as to admit of a weight of 32 ounces 

 being applied, before that pressure could be 

 overcome and the valve raised. 



Valves of various smaller sizes were now tried, 



