71. It was reserved for the genius of Newton to show us why the planets should obey these laws, and to reduce the planetary system under the domain of ordinary mechanics. He succeeded in showing that every mass of matter attracts every other mass with a force which is directly proportional to the product of the masses, and inversely proportional to the square of the distance, and that this universal force accounts, not only for Kepler’s laws of planetary motion but, for the orbit of the moon, as well as for that of a projectile discharged near the surface of the earth. 72. If we now pause for a moment, and review the progress of this investigation, we shall see that it began with a disposition to regard simplicity of motion as the test of truth, and when the Copernican system showed that our point of view is a movable one, it was at first thought that this would explain all departures from absolute simplicity. But Tycho Brahe and Kepler soon showed that the planets do not move in circles, and we now know that their motions, as well as that of the moon, can only be represented by curves of extreme complexity. Simplicity of motion has disappeared, but it has been replaced by simplicity of inter-relation between the various members of the system which are supposed to attract each other according to a simple and definite law. This law may be supposed to contain in itself implicitly all the various and complicated motions of the solar system. If applied to the past it will enable us to ascertain the exact date of the antient historical eclipses; if applied to the future it will enable us to foretell all but catastrophic astronomical occurrences. 73. Let us now turn to another branch of the same subject. When Galileo first applied his telescope to the sun, he discovered the existence of sun-spots. Their solar origin was however for some time disputed, the schoolmen of that day, holding resolutely to the dicta of Aristotle, being indisposed to believe that there could possibly be any imperfection in the sun. The telescope alone was in fault. There was even a sermon preached on Galileo, the text of which was ‘Viri Galilæi, quid statis in coelum spectantes?’ However, as time went on, observation showed that spots were unmistakably solar phenomena, and these very imperfections are made use of by modern science to obtain for us information regarding the chemical and physical structure of our luminary. It also appears that the position and size of these spots depend upon the positions of the planets Mercury and Venus, and this as well as other phenomena indicate the existence of some mysterious bond between the sun and the various members of his system, possibly other than the law of gravitation, as we now understand it, can express.[31] In fine, simplicity of relation threatens to disappear, just as simplicity of motion disappeared before it.