One may safely state thatevery material flows under certain conditions. It has been proved that this holds good forevery solid, even for extremely brittle materials, which under ordinary conditions crumble to pieces as soon as the stress applied exceeds the cohesion. The condition under which such a material has to be placed to make it flow is a sufficiently high pressure acting on all sides. The brittleness then disappears and the material, instead of being friable, flows, like any plastic substance. This has been shown for cubes of marble by Karman.