The possession by the planet of the nebulous matter, which we have already suggested is composed of the denser parts of the Aether around the planet, would give to the planet a nebulous appearance which would satisfactorily account for the term already given. They would indeed be what Sir John Herschel suggested they were, viz, planetary nebulae. _Spiral Nebulae._--The Spiral, or Whirlpool Nebulae, are remarkable objects, and were first discovered by Lord Rosse with his six-foot telescope. One of the best examples of the spiral nebulae is that known as 51M. Small telescopes show this as two clusters, one of them being surrounded by a ring, at a distance, which is divided into two parts. Lord Rosse, however, found it to be really a spiral nebula, the ring running into a series of spiral coils of nebulous matter, the outlying parts being connected with the main part by curved bands. Huggins has found that the spectrum of this nebula is not gaseous. Other examples of this class are 99M and 33M. What these spiral or whirlpool nebulae are, is unknown, but, on the hypothesis of a condensing and gravitating Aether which is in a state of rotation, the spiral nebulae can be easily pictured. For, as the condensation goes on, rotation will set in, and if we can picture such a phenomenon taking place in a plane which is at right angles to the line of vision, then we should have a full view of a nebula which would present a spiral form. Indeed, there is no phenomenon in connection with nebulae that cannot be physically explained by a condensing, gravitating and rotatory Aether; and as Aether is universal, the same properties will apply to it in distant space as they do in the solar system; and apart from a gravitating and rotatory electro-magnetic Aether, the phenomena of our own solar system cannot be physically conceived or explained. Therefore, if such an Aether can explain the phenomena associated with our own system, it ought also to explain, and that to the fullest extent, all phenomena incidental to and associated with the innumerable systems that flood the universe at large. [Footnote 44: _Outlines of Astronomy._] CHAPTER XIV UNITY OF UNIVERSE ART. 123. _The Universe._--In the preceding chapters we have endeavoured to deal with some of the principal phenomena that help to give a mechanical conception to the entire Universe. It now remains for us to show, in this last chapter, how, underlying all the physical structure of the Universe, there is one fundamental and primordial medium, in which all the forms of matter and motion find their ultimate unity. The Universe literally means one ultimate whole, though that whole may be compounded of many parts, the very essence of the term embodying the idea of a complete unity which runs throughout its whole physical structure.