A third congruity formerly believed in has suffered a like fate; to wit, that satellites always moved in or near the equatorial plane of their primary. All those first discovered did; the four large ones of Jupiter, the main ones of Saturn, and probably those of Uranus and Neptune. Even the satellites of Mars conformed. Iapetus alone seemed to make exception, and that by a glossable amount. But this orderliness, too, has been disposed of, only, like the others, to experience a resurrection in a different form. [Illustration] On examining more precisely the inclinations of these orbits some years ago, an interesting relation between them and the distances of the satellites from their primaries forced itself on my notice. The tilt increased as the distance grew. The only exceptions were very tiny bodies occupying a sort of asteroidal relation to the rest. A diagram will make this clear. The kernel of it dates from the lectures then delivered before the Massachusetts Institute of Technology in 1901. The interesting thing now about it is that the congruity there pointed out has been conformed to by every satellite discovered since,—the sixth, seventh, and eighth of Jupiter and the ninth and tenth of Saturn. It is evident that we already know enough of the geniture of our system to prophesy something about it and have the prophecy come true. Closely connected with the previous relation is a fourth concordance clearly of mechanical origin, the relation of the orbital eccentricities of the satellites to their distances from their respective planets. The satellites pursue more and more eccentric orbits according as they stand removed from planetary proximity. A fifth congruity is no less striking. All the satellites of all the planets that we can observe well enough to judge of turn the same face always to their lords. That the Moon does so to the Earth is a fact of everyday knowledge, and the telescope hints that the same respectful regard is paid by Jupiter’s and Saturn’s retinues to them. What is still more remarkable, Mercury and Venus turn out to observe the like vassal etiquette with reference to the Sun. And it will be noticed that they stand to him the nearest of his court. Here, then, is a law of proximity which points conclusively to some well-established force. Last is a remarkable congruity which study disclosed to me likewise some years ago, and which has received corroboration in discoveries since. This congruity is the peculiar arrangement of the masses in the solar system.