“Everybody knows that the nebular hypothesis, as it is to-day, draws its strongest support from spectroscopic facts. There shine the nebulæ in the heavens, and the spectroscope tells us what they really are, namely, vast clouds of incandescent gas, mainly, if not entirely, hydrogen and nitrogen. If we attempt to trace the chain of evolution through which our planet is supposed to have grown, we shall find the sky is full of intermediate forms. The nebulæ themselves appear to be in various stages of development; the fixed stars or suns differ widely in chemical constitution and in temperature; our earth is most complex of all. There are no ‘missing links’ such as the zoologist longs to discover when he tries to explain the origin of species. First, we have a nebula containing little more than hydrogen, then a very hot star with calcium, magnesium, and one or two other metals added; next comes a cooler sun in which free hydrogen is missing, but whose chemical complexity is much increased; at last we reach the true planets with their multitudes of material forms. Could there well be a more straightforward story? Could the unity of creation receive a much more ringing emphasis? We see the evolution of planets from nebulæ still going on, and parallel with it an evolution of higher from lower kinds of matter. “Just here, perhaps, is the key to the whole subject. If the elements are all in essence one, how could their many forms originate save by a process of evolution upward? How could their numerous relations with each other, and their regular serial arrangements into groups, be better explained? In this, as in other problems, the hypothesis of evolution is the simplest, most natural, and best in accordance with facts.”[75] [Footnote 75: _Popular Science Monthly_ for February 1876. See also the January number for 1873.] _Dr. G. Johnstone Stoney on the pre-nebular condition of matter._—Further evidence that all the chemical elements were probably evolved from one common source, is furnished by Dr. G. Johnstone Stoney’s “Logarithmic Law of Atomic Weights,” a theory recently advanced in a communication to the Royal Society.[76] A cardinal feature of this investigation is that in it atomic weights are represented by volumes, not by lines. A succession of spheres are taken whose volumes are proportional to the atomic weights, and which may be called _the atomic spheres_. When the radii of these spheres are plotted down on a diagram as ordinates, and a series of integers as abscissas, the general form of the logarithmic curve becomes apparent; and close scrutiny has shown that either the logarithmic curve, or some curve lying very close to it, expresses the real law of nature. [Footnote 76: _Proc. Roy. Soc._ for April 19, 1888, p. 115.]