Abstract

Gravity was a major theme in the seventeenth century scientific discussion. Trendsetters in the renewal of natural science were Galilei and Descartes. The first required a unified theory of all phenomena of gravity ; the second provided one with his vortex-hypothesis, which explained gravity by the mechanical push of subtile bodies of the vortex. This conception was tested and generally followed by Christiaan Huygens, whereas Newton presented the laws of the so called 'attraction' by which he did not at all indicate the causes of those laws of motion. Spinoza comes on the scene of polemics as a critical Cartesian. Motion (of which downward motion of heavy bodies is only one instance) was explained by Descartes, but not so the rest of bodies or the equilibrium in the power relation between opposite forces, neither the reason why in some cases the particles form a hard body. Full fledged mechanism and consistent determinism lead Spinoza to account for rest and solidity in the same way, namely by means of the pressure of small and mostly unvisible bodies in the whirling environment. This paradoxical law was acknowledged as a real and important contribution to physical science by the Dutch spinozistic Cartesians Cuffeler and Overkamp, by the mathematician De Volder, by Spinoza's younger friend Tschirnhaus and in France by Malebranche. By the end of the century it was quite normal to speak about „the gravity of the air” and to consider the gravity of gross bodies as an illusion