Of course, in our system the center of attraction is the nucleus of the sun. The mass of this body increases rapidly, as also its power of attraction. Of the particles gravitating to it the heavier become heaped up in the center. In falling from different heights toward this common focus the particles cannot have such perfect equality of resistance that no lateral movements should be set up. A general circulatory motion is in fact established ultimately in one direction about the central mass, which receiving new particles from the encircling current rotates in harmony with it. Mutual interference in the particles outside the mass of the sun prevents all accumulation except in one plane and that takes the form of a thin disk continuous with the sun's equator. In this circulating vaporous disk about the sun differences of density give rise to zones not unlike the rings of Saturn. These zones ultimately contract to form planets, and as the planets are thrown off from the central solar mass till an equilibrium is established between the centripetal and centrifugal forces, so the satellites in turn are formed from the planets. The comets are to be regarded as parts of the system, akin to the planets, but more remote from the control of the centripetal force of the sun. It is thus that Kant conceived the nebular hypothesis, accounting (through the formation of the heavenly bodies from a cloudy vapor similar to that still observable through the telescope) for the revolution of the planets in one direction about the sun; the rotation of sun and planets; the revolution and rotation of satellites; the comparative densities of the heavenly bodies; the materials in the tails of comets; the rings of Saturn, and other celestial phenomena. Newton, finding no matter between the planets to maintain the community of their movements, asserted that the immediate hand of God had instituted the arrangement without the intervention of the forces of Nature. His disciple Kant now undertook to explain an additional number of phenomena on mechanical principles. Granted the existence of matter, he felt capable of tracing the cosmic evolution, but at the same time he maintained and strengthened his religious position, and did not assume (like Democritus and Epicurus) eternal motion without a Creator or the coming together of atoms by accident or haphazard.