The idea that the nebulæ were far more remote from us than the stars long held sway, even after it had been given up by its chief supporter. When Sir William Herschel, by means of his then unapproached telescopic power, resolved the Milky Way more or less completely into stars, and showed that numerous objects which had been classed as nebulæ were really clusters of stars, it was natural to suppose that those which still retained their cloudy appearance under the highest telescopic powers were also clusters or systems of stars, which only needed still higher powers to show their true nature. This idea was supported by the fact that several nebulæ were found to be more or less ring-shaped, thus corresponding on a smaller scale to the form of the Milky Way; so that when Herschel discovered thousands of telescopic nebulæ, he was accustomed to speak of them as so many distinct universes scattered through the immeasurable depths of space. Now, although any real conception of the immensity of the one stellar universe, of which the Milky Way with its associated stars is the fundamental feature, is, as I have shown, almost unattainable, the idea of an unlimited number of other universes, almost infinitely remote from our own and yet distinctly visible in the heavens, so seized upon the imagination that it became almost a commonplace of popular astronomy and was not easily given up even by astronomers themselves. And this was in a large part due to the fact that Sir William Herschel's voluminous writings, being almost all in the Philosophical Transactions of the Royal Society, were very little read, and that he only indicated his change of view by a few brief sentences which might easily be overlooked. The late Mr. Proctor appears to have been the first astronomer to make a thorough study of the whole of Herschel's papers, and he tells us that he read them all over five times before he was able thoroughly to grasp the writer's views at different periods. But the first person to point out the real teaching of the facts as to the distribution of the nebulæ was not an astronomer, but our greatest philosophical student of science in general, Herbert Spencer. In a remarkable essay on 'The Nebular Hypothesis' in the _Westminster Review_ of July, 1858, he maintained that the nebulæ really formed a part of our own Galaxy and of our own stellar universe. A single passage from his paper will indicate his line of argument, which, it may be added, had already been partially set forth by Sir John Herschel in his _Outlines of Astronomy_.