on the Cohesion of Fluids. 6y 
from it by means of their cohesion, in the same manner as, 
when water is supported by the atmospheric pressure in an 
inverted vessel, the outside of the vessel sustains a hydrostatic 
pressure proportionate to the height ; and this pressure must 
remain unaltered, when the water, having been sufficiently 
boiled, is made to retain its situation for a certain time by its 
cohesion only, in an exhausted receiver. When, therefore, the 
surface of the fluid is terminated by tw r o right lines, and has 
only a simple curvature, the curvature must be every where 
as the ordinate ; and where it lias a double curvature, the sum 
of the curvatures in the different directions must be as the 
ordinate. In the first case, the curve may be constructed by 
approximation, if we divide the height at which it is either 
horizontal or vertical into a number of small portions, and 
taking the radius of each portion proportional to the reciprocal 
of the height of its middle point above or below the general 
surface of the fluid, go on to add portions of circles joining 
each other, until they have completed as much of the curve as 
is required. In the second case, it is only necessary to consider 
the curve derived from a circular basis, which is a solid of 
revolution ; and the centre of that circle of curvature, which is 
perpendicular to the section formed by a plane passing through 
the axis, is in the axis itself, consequently in the point where 
the normal of the curve intersects the axis : we must therefore 
here make the sum of this curvature, and that of the generating 
curve, always proportional to the ordinate. This may be done 
mechanically, by beginning at the vertex, where the two cur- 
vatures are equal, then, for each succeeding portion, finding 
the radius of curvature by deducting the proper reciprocal of 
the normal, at the beginning of the portion, from the ordinate, 
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