2. Anchoring laws

Placed on a table, a little liquid sometimes spreads and thins to the point of disappearing from view, and in other cases forms a small drop. What determines the behavior of the liquid is its ability to take on the shape of the solid it is placed in contact with; in other words, the possibility of replacing one surface (that of the solid, which is dry at the start of the experiment) with two (one between the solid and the liquid, the other between the liquid and the air). It is therefore natural, as the Italian physicist Marangoni proposed around 1870, to compare the surface energies involved in this problem (figure 3 ).

Let S be the spreading parameter that compares the surface energies...