Apart from some such hypothesis as will be suggested in this chapter, that ultimate unity is incapable of a physical or mechanical conception. In Art. 29 we learned that the Universe was composed of two classes of things, matter and motion, while in Art. 30 we learned that the sum total of matter according to the law of the conservation of matter ever remains the same; while further, in Art. 53, according to the law of the conservation of energy, the sum total of energy ever remains the same. We have also learned that the two are indissolubly united, so that wherever we found matter, whether that matter was in its atomic, molecular, planetary or stellar form, there, as its necessary complement and counterpart, was the ever-present and unceasing motion, in one or other of its many forms. Thus, throughout the entire Universe, we find the same two essentials ever working in unison and harmony. Nowhere in the realm of infinite space is there such a phenomenon as rest or absolute death. The ideal that seems to be the key of the Universe, is that continuity of motion which science teaches us is so inseparably connected with all matter. Grouped, however, here and there throughout the Universe are modifications of this aetherial matter, termed molecules, satellites, planets, suns, or stars, which modifications are, however, not so real and abiding as the electro-magnetic Aether from which they receive their physical origin. The physical character of the universe is progressive. Even in its ultimate unity there is no such thing as stagnation or standing still; for, while in some parts of the Universe new stars and suns and planets, yea, even new systems are being evolved out of the primordial Aether, in other parts of the Universe old stars and suns, with all their attendant planets and satellites, are passing on towards that final end, when they themselves will be again resolved into the original form of matter from which they were first made. This assertion is in perfect harmony not only with science, but also with revelation. For even revelation teaches us that all the stars shall grow old as doth a garment, and as a vesture shall they be folded up (Heb. i. 11), and that (out of their ruins) a new heaven and a new earth shall be created and the former shall not be remembered (Isaiah lxv. 17).