Hence, by the law of action and re-action, each body is itself the centre of an attractive force extending indefinitely in space, whence proceed all the mutual disturbances which render the celestial motions so complicated, and their investigation so difficult.
The gravitation of matter, directed to a centre, and attracting directly as the mass and inversely as the square of the distance, does not belong to it when considered in mass only; particle acts on particle according to the same law when at sensible distances from each other. If the sun acted on the centre of the earth without attracting each of its particles, the tides would be very much greater than they now are; and would also, in other respects, be very different. The gravitation of the earth to the sun results from the gravitation of all its particles, which, in their turn, attract the sun in the ratio of their respective masses. There is a reciprocal action likewise between the earth and every particle at its surface; were this not the case, and were any portion of the earth, however small, to attract another portion, and not be itself attracted, the centre of gravity of the earth would be moved in space by this action, which is impossible.
The forms of the planets result from the reciprocal attraction of their component particles. A
