92 Inquiries into the Principles of Liquid Attraction > 



of a liquid never rests in a horizontal position, when it comes in con- 

 tact with any substance ; but is always either elevated or depressed." 



If water be carefully poured into a vessel whose bottom is diy, it 

 rises nearly to the height to which drops attain, and then spreads lat- 

 erally, as the quantity of water increases, having its edges curved 

 downward through the influence of the contractile surface ; so that 

 when it meets the sides of the vessel it has the appearance of de- 

 pression. (See Fig. 8.) Now as it comes in contact with the sides 

 of the vessel, the surface of the liquid makes new angles with the 

 vessel, and, if the surface of the vessel has a sufficiently strong at- 

 traction for the surface of the liquid, an elevation of the liquid sud- 

 denly takes place, which is usually so rapid as to render its progress 

 difficult to be observed. When the elevation commences, the de- 

 pressed curve begins to shorten, and does not stop shortening till it 

 vanishes, and then it is succeeded by an upward curve, which con- 

 tinues to rise contiguous to the sides of the vessel, till it attains its 

 maximum height ; and this is when it has risen as much above the 

 common surface as it was at first depressed below it; (See Fig. 9.) 

 and in which situation, it has the apparently uniform curve of the 

 parabola. 



Now as the curve of the surface moves upward, at the sides of the 

 vessel, it necessarily acts against the pressure of the atmosphere, and 

 performs an office similar to that which the piston of a common pump 

 performs, diminishing the pressure on the liquid under the curved 

 surface, contiguous to the sides of the vesspl ; but because the uni- 

 form pressure of the atmosphere is not sensibly diminished on the 

 liquid under the surface, at a distance from the sides of the vessel, 

 it forces the liquid up under the elevated surface, where it is sus- 

 tained by the pressure of the atmosphere. 



2nd. Let us observe how these principles account for the phenom- 

 ena connected with the fourth law, viz : " two bodies floating on a li- 

 quid, both of which have an elevation of the liquid, will, when near, 

 approach each other with a column of liquid rising between them." 



It is a well kno\vn fact, that the lateral pressure of a column of 

 water under the piston of a common pump, diminishes in the same 

 ratio as the point pressed rises above the base of the column ; and if 

 we suppose the piston of a pump to take off the pressure of the at- 

 mosphere thirty two feet, the lateral pressure will diminish from a 

 pressure represented by 32 at the base of the column, till the point 

 pressed arrives at the lop, where the lateral pressure may be repre- 



