cate the mathematical relation
between the attraction of individual particles and the final result.
Leslie's theory was afterwards treated according to Laplace's
mathematical methods by James Ivory in the article on capillary action,
under "Fluids, Elevation of," in the supplement to the fourth edition of
the _Encyclopaedia Britannica_, published in 1819.

In 1804 Thomas Young (Essay on the "Cohesion of Fluids," _Phil. Trans._,
1805, p. 65) founded the theory of capillary phenomena on the principle
of surface-tension. He also observed the constancy of the angle of
contact of a liquid surface with a solid, and showed how from these two
principles to deduce the phenomena of capillary action. His essay
contains the solution of a great number of cases, including most of
those afterwards solved by Laplace, but his methods of demonstration,
though always correct, and often extremely elegant, are sometimes
rendered obscure by his scrupulous avoidance of mathematical symbols.
Having applied the secondary principle of surface-tension to the various
particular cases of capillary action, Young proceeded to deduce this
surface-tension from ulterior principles. He supposed the particles to
act on one another with two different kinds of forces, one of which, the
attractive force of cohesion, extends to particles at a greater distance
than those to which the repulsive force is confined. He further supposed
that the attractive force is constant throughout the minute distance to
which it extends, but that the repulsive force increases rapidly as the
distance diminishes. He thus showed that at a curved part of the
surface, a superficial particle would be urged towards the centre of
curvature of the surface, and he gave reasons for concluding that this
force is proportional to the sum of the curvatures of the surface in two
normal planes at right angles to each other.

The subject was next taken up by Pierre Simon Laplace (_Mecanique
celeste_, supplement to the tenth book, pub. in 1806). His results are
in many respects identical with those of Young, but his methods of
arriving at them are very different, being conducted entirely by
mathematical calculations. The form into which he threw his
investigation seems to have deterred many able physicists from the
inquiry into the ulterior cause of capillary phenomena, and induced them
to rest content with deriving them from the fact of surface-tension. But
for those who wish to study the molec