Let us therefore apply the centripetal force, or Gravitation Attraction, to the solar system, and see how it works out. The law strictly defined is given in Art. 18, from which we learn that the attractive force between two bodies is as the product of their masses. Now what are the masses of some of the bodies in the solar system? We find that the sun, with its diameter of 865,000 miles, is about 324,000 times greater in mass than our earth, so that it would take about 324,000 bodies of the size and density of our earth to equal a body of the size and density of the sun. It has been calculated, however, by Von Asten, from observations made on comets by the planet Mercury, that the mass of Mercury is about 1/24 of the mass of the Earth. Therefore the mass of the sun must exceed the mass of Mercury 324,000 × 24 = 7,776,000; the exact relation according to Von Asten is 7,636,440. Again, the planet Jupiter, with its diameter of 85,000 miles and its density of 1·38, is only 1/1048 part of the mass of the sun, so that it would take about 1048 Jupiters to equal the mass of the sun, therefore Jupiter must weigh about 7400 times the mass of Mercury. If the mass of Mercury, therefore, be represented by 1, the mass of the Earth would be represented by 24, the mass of Jupiter by 7400, and the mass of the sun by 7,636,400. So that the attractive forces between the planets as regards their masses only will be represented numerically as follows-- Sun and Mercury 7,636,400 × 1 = 7,636,400. Sun and Earth 7,636,400 × 24 = 190,008,000. Sun and Jupiter 7,636,400 × 7,400 = 56,435,360,000. Thus we see that the attractive force between the sun and the earth exceeds 24 times the attractive force between the sun and Mercury, while the attractive force of gravity between the sun and Jupiter is 7400 times greater than the attractive force between the sun and Mercury, relative to their masses. Therefore, according to the Law of Gravity, as regards the masses of bodies, Jupiter and the sun should be nearer together than Mercury and the sun, because their attractive powers are greater, and the earth and the sun should be nearer together than Mercury and the sun, because their joint attractive powers are also greater. In the same way it can be proved that all the other planets whose masses are greater than Mercury ought, according to the Law of Gravity in regard to masses only, to be nearer to the sun than what Mercury is, simply because the total attractive forces between any two are greater than the attractive force between Mercury and the sun. The respective masses of the planets compared with the sun, taking the mass of the sun as unity, are as follows-- Jupiter 1/1,048 of mass of sun. Saturn 1/3,529 " " Neptune 1/18,520 " " Uranus 1/22,020 " " Earth 1/324,439 " " Venus 1/397,000 " " Mars 1/2,994,790 " " Mercury 1/7,636,440 " "