It was he who solved the problem of oblique forces, and who discovered the important hydrostatic principle that the pressure of fluids is proportionate to their depth, without regard to the shape of the including vessel.
The study of oblique forces was made by Stevinus with the aid of inclined planes.

His most demonstrative experiment was a very simple one, in which a chain of balls of equal weight was hung from a triangle; the triangle being so constructed as to rest on a horizontal base, the oblique sides bearing the relation to each other of two to one.

Stevinus found that his chain of balls just balanced when four balls were on the longer side and two on the shorter and steeper side.

The balancing of force thus brought about constituted a stable equilibrium, Stevinus being the first to discriminate between such a condition and the unbalanced condition called unstable equilibrium.

By this simple experiment was laid the foundation of the science of statics.