70 
Dr, Young's Essay 
square of the greatest ordinate being eqUal to twice the appropriate 
rectangle , and the greatest ordinate to twice the diameter of the cor- 
responding circle of curvature : so that, if 'we suppose a circle to be 
described, having this ordinate for a diameter, the chord of the 
angular elevation in this circle will be always- equal to the ordinate 
at each point, and the ordinate will vary as the sine, of half the angle 
of elevation, whenever the curve has an asymptote, Mr. Fuss has 
demonstrated, in the third volume of the Acta Petropolitanai 
some properties of the arch of equilibrium under the pressure 
of a fluid, which is the same as one species of the curves 
here considered. The series given by Euler in the second 
part of the same volume, for the elastic curve, may also be 
applied to these curves. 
IV. Application to the Elevation of particular Fluids . 
The simplest phenomena, which afford us data for deter- 
mining the fundamental properties of the superficial cohesion 
of fluids, are their elevation and depression between plates and 
in capillary tubes, and their adhesion to the surfaces of solids 
which are raised in a horizontal situation to a certain height 
above the general surface of the fluids. When the distance of 
a pair of plates, or the diameter of a tube, is very minute, the 
curvature may be considered as uniform, and the appropriate 
rectangle may readily be deduced from the elevation, recol- 
lecting that the curvature in a capillary tube is double, and the 
height therefore twice as great as between two plates. In the 
case of the elevation of a fluid in contact with a horizontal 
surface, the ordinate may be determined from the weight 
required to produce a separation; and the appropriate rectangle 
may be found in this manner also, the angle of contact being 
