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 the 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 without the tube, 
must force up the 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 asa 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 1s 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- 
