Page:Sir William Herschel, his life and works (1881).djvu/111

Rh "In an investigation of this delicate nature we ought to avoid two opposite extremes. If we indulge a fanciful imagination, and build worlds of our own, we must not wonder at our going wide from the path of truth and nature. On the other hand, if we add observation to observation without attempting to draw not only certain conclusions but also conjectural views from them, we offend against the very end for which only observations ought to be made. I will endeavor to keep a proper medium, but if I should deviate from that, I could wish not to fall into the latter error." (1785.)

"As observations carefully made should always take the lead of theories, I shall not be concerned if what I have to say contradicts what has been said in my last paper on this subject." (1790.)

No course of reasoning could be more simple, more exact, more profound, and more beautiful than this which follows:

"As it has been shown that the spherical figure of a cluster is owing to the action of central powers, it follows that those clusters which, cæteris paribus, are the most complete in this figure, must have been the longest exposed to the action of these causes. Thus the maturity of a sidereal system may be judged from the disposition of the component parts.

"Hence planetary nebulæ may be looked on as very