Inquiries into the Principles of Liquid Attraction. 95 



surface of the column of liquid, which acts as a lifting piston, as before 

 described ; to which there is also added the force of another surface 

 at the bottom of the column which acts as a forcing piston, and in 

 concert with which tlie atmosphere acts, which, when the tube rested 

 on the water, acted indirectly, but now directly, to sustain the column ; 

 but this elevation will be the case in a less degree, except when the 

 sides of the tube, at the bottom, are extremely thin. (See Fig. 11.) 



Having considered the various laws and properties of liquid attrac- 

 tion, as they occur in the open atmosphere, it now remains to exam- 

 ine them as they may be observed in a rarer medium, particularly 

 when under the exhausting influence of the air pump. Now if we 

 suppose the common atmosphere entirely removed, and a new one 

 formed, by the evaporation of some liquid placed under the receiver 

 of an air pump, the pressure of this new atmosphere, which for the 

 sake of distinction may be called artificial, will depend on the degree 

 of temperature, and on the different degrees of volatility which the 

 different liquids used possess ; whether they be ether, alcohol, or any 

 other. If for example, we take the atmosphere formed from water 

 at a medium temperature, and suppose the pressure of this to be 

 equal to the pressure of a column of water of six inches, and if we 

 suppose the upper and elevating surface in a capillary tube of suffi- 

 ciently fine bore, to take off the whole pressure of the artificial at- 

 mosphere from the column of liquid in the tube, the pressure of the 

 atmosphere which rests on the surface of the liquid ivithout the tube, 

 must force up tlie liquid the whole height to which this pressure can 

 sustain, viz. six inches. But if the bores of the tubes are larger, the 

 height to which it will rise will be proportionally less. If the column 

 of liquid in the capillary tube, in the open atmosphere, be broken by 

 a portion of common air ; the upper portion of the column of liquid 

 will have both its upper and under surfaces concave, the former act-> 

 ing as a lifting piston upwards and the latter downwards, and the sep^ 

 aration will remain permanent. (See Fig. 13.) But if a separation 

 of the column of liquid should happen in the tube, under the receiver 

 of an air pump, by unequal degrees of temperature in the evapora^ 

 ting process ; the artificial atmosphere will be condensed by the 

 equalization of the temperature, and will allow the column to reunite. 



Bodies floating on liquids where the common atmosphere is re- 

 moved, obey the same laws as when in the open air ; that is, when 

 both have an elevation, or both a depression of the liquid, they ap~ 



