The observations of the famous astronomer, Sir William Herschel, which resulted in the discovery of binary or double stars, of star-clusters, and cloud-like nebulæ (as that term implies) were further confirmations of Kant's theory. And such modifications in this as have been made by subsequent advance in knowledge, notably by the doctrine of the Conservation of Energy (the hypothesis of Kant and Laplace being based on gravitation alone), affect not the general theory of the origin of the heavenly bodies from seemingly formless, unstable, and highly-diffused matter. The assumption of primitive unstableness and unlikeness squares with the unequal distribution of matter; with the movements of its masses in different directions, and at different rates; and with the ceaseless redistribution of matter and motion. For all changes of states are due to the rearrangement of the atoms of which matter is made up, resulting in the evolution of the seeming like into the actual unlike; of the simple into the more and more complex, till--speaking of the only planet of whose life-history we can have knowledge--with the cooling of the earth to a temperature permitting of the evolution of living matter, the highest complexity is reached in the infinitely diverse forms of plants and animals. Therefore, as our knowledge of matter is limited to the changes of which we assume it to be the vehicle, it would seem that science reduces the Universe to the intelligible concept of Motion. Since the great discovery by Kirchoff, in 1859, of the meaning of the dark lines that cross the refracted sun-rays, the spectroscope has come as powerful evidence in support of the nebular theory, while the photographic plate is a scarcely less important witness. The one has demonstrated that many nebulæ, once thought to be star-clusters, are masses of glowing hydrogen and nitrogen gases; that, to quote the striking communication made by the highest authority on the subject, Dr. Huggins, in his Presidential Address to the British Association, 1891, "in the part of the heavens within our ken, the stars still in the early and middle stages of evolution exceed greatly in number those which appear to be in an advanced condition of condensation." The other, recording infallible vibrations on a sensitive plate, and securing accurate registration of the impressions, reveals, as in Dr. Roberts's grand photograph of the nebula in Andromeda, a central mass round which are distinct rings of luminous matter, these being separated from the main body by dark rifts or spaces. To quote Dr. Huggins once more, "We seem to have presented to us some stage of cosmical Evolution on a gigantic scale."