The investigations in capillarity stem back as far as Leonardo da Vinci, however the idea of capillary length was not developed until much later. Fundamentally the capillary length is a product of the work of Thomas Young and Pierre Laplace. They both appreciated that surface tension arose from cohesive forces between particles and that the shape of a liquids surface reflected the short range of these forces. At the turn of the 19th century they independently derived pressure equations, but due to notation and presentation, Laplace often gets the credit. The equation showed that the pressure within a curved surface between two static fluids is always greater than that outside of a curved surface, but the pressure will decrease to zero as the radius approached infinity. Since the force is perpendicular to the surface and acts towards the centre of the curvature, a liquid will rise when the surface is concave and depress when convex. This was a mathematical explanation of the work published by James Jurin in 1719, where he quantified a relationship between the maximum height taken by a liquid in a capillary tube and its diameter – Jurins law. The capillary length evolved from the use of the Laplace pressure equation at the point it balanced the pressure due to gravity, and is sometimes called the Laplace capillary constant, after being introduced by Laplace in 1806.