It must, however, be borne in mind that the attraction between bodies is mutual, proportioned to their masses and distances. While the sun attracts the planets toward himself, they also attract the sun, though their effect is comparatively small, owing to the vastness of the solar mass. The planets likewise act upon each other; and as their relative distances are perpetually varying, certain perturbations are caused in the system, which, though minute in each particular case, become considerable by accumulation, and yet are ultimately corrected and repaired by the same cause that produces them. Newton left to posterity the task of thoroughly investigating these inequalities, of showing them to be a result of the law of gravitation, and establishing the permanence of the system, notwithstanding the accumulating influence of its internal disturbances. He himself had no gleam of the latter truth, but seems to have entertained an opinion that the irregularities occasioned by the mutual action of the planets and comets would probably go on increasing till the system either wrought out its own destruction or received reparation from the direct intervention of its Creator. But Euler, Clairaut, D’Alembert, Lagrange, and Laplace, have demonstrated the problem that the perturbations of the planets are periodic in their nature, that accurate compensation for them is laid up in store, so that the system is not arranged upon a principle of self-destruction. The elements of disorder and decay are removed from it. The very conditions of its existence guarantee its stability till the will of the great Ruler shall be expressed to the contrary. When an end shall come to its present constitution, that will not be the effect of its own faulty architecture, but of the fiat of Omnipotence. [Illustration: =Room in which Newton was born.=]