That liquids, if finitely compressible, must (at any one temperature) become steadily less compressible as the pressure is raised, seems to be obvious without any attempt at proof. Yet the assertion is even now generally made, mainly in consequence of an erroneous statement of Örsted, which has been supported by some comparatively recent investigations of Cailletet and others, that the compressibility of water (at any one temperature) is practically the same at all pressures not exceeding a few hundred atmospheres.