P Y R 



\itmn of water, having the same base as the piston, and an altitude equal 

 to that of the surface of the water in the body of the pump above that in 

 the reservoir. 



2. In a sucking pump, if the height of the lower or fixed valve above 

 the surface of the water #, the length of the stroke of the piston b, 

 and the height of a column of water in equilibrium with the pressure of 

 the atmosphere = h, the height to which the water is raised by the 

 first stroke is 



a 4. b + h V( + b -f. h}* kbh 

 2 



3. The same notation being retained, and c being put for a -f b or tire 

 greatest height to which the piston ascends, b must be greater than 



j-r- otherwise the water will not rise above the piston. 



4. Height to which water will rise in a vacuum in different states of 

 the barometer. 



Barom. in inches. Height of water in feet. 



28 ,,,~.,~wyv w ^ w ~,~ w 31.66 



28| w 32.23 



29 32.79 



29| 33.36 



30 33.92 



30| 34.49 



31 ,~~~~ ~~ 35.05 



Hence the valve of the piston in the common pump must be nearer to 

 the surface of the water in the reservoir than 33 feet, otherwise the wa- 

 ter can never rise above it. 



PYROMETER, Wedgwood's, for measuring very high temperatures. 



The scale of this Pyrometer, or the point marked commences at red 

 heat fully visible in day light, and is equivalent to 1077|o of Fahrenheit's 

 scale, and one degree of the former is = 130 of the latter. The extre- 

 mity of Wedgwood's scale is 240, but the highest heat he measured with 

 it is 160. It appears .'. that this pyrometer includes an extent of about 

 32000 of Fahrenheit's degrees, or about 54 times as much as that between 

 the boiling and freezing points of mercury, by which mercurial ones are 

 naturally limited ; that if the scale be produced downward in the same 

 manner as Fahrenheit's has been supposed to be produced upward for an 

 ideal standard, the freezing point of water would fall nearly 8 below 

 221 N2 



