Omitting discussion of the technical difficulties in the application of the nebular theory to demonstrated facts, which may be found in the books, we may again repeat that this theory is not essential to account for the heat of the sun, which finds its real source elsewhere, while, nevertheless, the theory in itself is not incompatible with the views which we have endeavored to present and demonstrate. Certain phenomena, however, have been considered in prior quotations in this work which may aid us to roughly indicate the successive processes by which the evolution of solar systems and galaxies may be explained on another basis which requires no violent assumptions to be made and no suspension of any of nature's universal laws. The same operations which we see around us at the present time in our own system, if extended to the dimensions of a nebular aggregation, would probably present the same phenomena as those we find partially disclosed in the gaseous nebulæ, particularly the spiral, and these would naturally determine the final production of solar systems such as our own. The gaseous nebulæ, not spiral, and the mixed nebulæ also, would fall into their appropriate categories in the same general plan, and a consistent mode of formation would be presented from the beginning to the end of the different processes. It should be observed that the spiral required by Laplace's nebular theory is essentially a centripetal spiral. The spiral nebulæ we see in the heavens, however, are centrifugal spirals. This is clearly shown in Plates XV., XII., and the frontispiece of Nichol's "Architecture of the Heavens," as well as in Plates XIII. and XIV. Plate XV.--the open spiral--is directly contradictory of any phenomena which could occur in accordance with the nebular theory of Laplace. The frontispiece shows the only form which such a nebula could assume at any stage of its career,--that is, a close spiral with nearly circular convolutions. But while this particular form is not only in entire accordance with the hypothesis which we are about to suggest, being in fact one of the later and necessary stages in its progress, any such spiral as that shown in Plate XV. is utterly out of the question in the application of the nebular theory of Laplace or in any of the more recent modifications thereof.