Page:Hector Macpherson - Herschel (1919).djvu/57

Rh nebulous star of the eighth magnitude in the constellation Taurus, surrounded by a faintly-luminous atmosphere of considerable extent. The results of his investigations and reflections were contained in his remarkable paper "On nebulous stars properly so-called," dated 1st January, 1791. In regard to the nebulous star in Taurus, he said: "Our judgment will be that the nebulosity about the star is not of a starry nature". If, he pointed out, the nebulosity consisted of very remote stars, which appear nebulous on account of great distance, "then what must be the enormous size of the central point which outshines all the rest in so superlative a degree as to admit of no comparison?" If, however, the star is of average size, the smaller points composing the nebulosity must be almost infinitesimal. "We therefore either have a central body which is not a star, or have a star which is involved in a shining fluid of a nature totally unknown to us. I can adopt no other sentiment than the latter." And with characteristic caution he added in the same paper: "If therefore this matter is self-luminous, it seems more fit to produce a star by its condensation than to depend on the star for its existence".

This was in 1791, five years before Laplace suggested his classical hypothesis at the close of the "Systeme du Monde". The germ of the nebular theory, therefore, was present in the mind of Herschel at this early stage. In the paper of 1791, Herschel proceeded to apply his new view to the various nebulous regions all over the heavens. He concluded that he had been too hasty in his former surmise that all nebulæ were distant clusters. If the "shining fluid" can exist without stars, "we may with great facility explain that very extensive telescopic nebulosity" in the constellation Orion. "What a field of novelty is here opened to our conceptions!"

In 1802 Herschel dealt with the subject again in his "Catalogue of 500 new nebulæ". But it was not till