436 



Explanation of the Theory of the 



[June, 



height will be equal to the difference of level of the two tranches ; 

 its specific gravity the same as that of the mercury. 



10. Any ratio of the height of a cylindrical column uniformly 

 dense is the same proportion of its weight, and of its volume. 



11. The diameters and weights of the two cylinders being- 

 equal, their heights will be reciprocally as their specific gravities. 

 The mean specific gravity of the column of the fluid in the vessel 

 W, intercepted between its surface and A, being less than that 

 of the mercury in the syphon, in the ratio of 20 to 1, the vertical 

 height of the fluid above A will exceed that of the difference of 

 level of the mercury in the same proportion. 



12. To ascertain the vertical 

 height of the section I) c situated 

 below the surface a of the fluid 

 contained in the vessel T; note the 

 heights (differences of level) of 

 the mercury in the syphons S and 

 S', placed at /> and c. Conceiving 

 the fluid above the level of b to be 

 removed, the difference of these 

 heights, in addition to the mean 

 specific gravity of the intercepted 

 fluid and that of the mercury, 

 form the whole of the requisite 

 data. 



Theory of the Barometer. 



13. Mercury (water, or other heavy incompressible fluid) being 

 poured into the vessel TJ, will ascend, and finally stand at the 



same vertical height, or level / 1, as well in the tube C, and in the 

 inverted syphon B fixed within it as in the vessel itself, and in 

 the erect tube D, and the inclined one A forming part of it. 

 14. The whole being in a vacuum, if we introduce ii\to the 



