Laplace in 1805

In the field of capillarity it is usual to consider together the work of Young and Laplace, and it is true that they both obtained some of the same important results within a year of each other. Their aims and methods were, however, quite different. In reading Young we are reading 18th century natural philosophy; in reading Laplace we are reading 19th century theoretical physics [1]. This ‘sea-change’ in the early years of the new century is as dramatic as that of the ‘scientific revolution’ of the 17th century, and was due to the efforts of the great French school of mathematical physics of that time [2]. This is not the place to discuss the origin of this second revolution but to concentrate only on how it led to a revival of the subject of cohesion and to a second period of advance. The man responsible was Laplace [3].

The prevailing opinion in France at the end of the 18th century was that of Buffon and his followers; the cohesive forces were probably gravitational in origin and so followed the inverse-square law at large distances but departed from that law at short distances where the shapes of the particles affected the interaction. In 1796 Laplace discussed this view in the first edition of his Exposition du système du monde, noting, however, that the particles of matter would have to be of an inconceivably high density and extremely widely spaced if matter was to have its observed degree of cohesion and its known density [4].