The epoch of mere astronomical discovery began with the detection of the large satellite of _Saturn_ by HUYGHENS, in 1655. Even then superstition was not dead. HUYGHENS did not search for more moons, because by that discovery he had raised the number of known satellites to six,[14] and because these, with the six planets, made "the perfect number twelve."
From 1671 to 1684 CASSINI discovered four more moons revolving about _Saturn_. Since 1684 no new body had been added to the solar system. It was thought complete for nearly a century.
In England, the remarkable discoveries of BRADLEY (1727-62) had been in the field of practical astronomy, and his example had set the key-note for further researches. France was just about beginning the brilliant period of her discoveries in mathematical astronomy, and had no observatory devoted to investigations like HERSCHEL'S, with the possible exception of DARQUIER'S and FLAUGERGUES'. The observatories of SCHROETER and VON HAHN, in Germany, were not yet active. The field which HERSCHEL was created to fill was vacant, the whole world over. It was especially so in England. The Royal Observatory at Greenwich, under MASKELYNE, a skilful observer, whose work was mostly confined to meridian observations, was no rival to a private observatory like HERSCHEL'S. The private observatories themselves were but small affairs; those of the king, at Kew, of Dr. WILSON, at Glasgow, of Mr. AUBERT, at Loampit Hill, of the Count VON BRUHL, in London, being perhaps the most important. The whole field was open. What was perhaps more remarkable, there was in England, during HERSCHEL'S lifetime, no astronomer, public or private, whose talents, even as an observer, lay in the same direction.
It hardly need be said that as a philosopher in his science, he had then no rival, as he has had none since. His only associates even, were MICHELL and WILSON.[15]
Without depreciating the abilities of the astronomers of England, his cotemporaries, we may fairly say that HERSCHEL stood a great man among a group of small ones.
Let us endeavor to appreciate the change effected in the state of astronomy not only in England but in the whole world, simply by the discovery of _Uranus_. Suppose, for example, that the last planet in our system had been _Saturn_. No doubt HERSCHEL would have gone on. In spite of one and another difficulty, he would have made his ten-foot, his twenty-foot telescopes. His forty-foot would never have been built, and the two satellites which he found with it might not have been discovered. Certainly _Mimas_ would not have been. His researches on the construction of the heavens would have been made; those were in his brain, and must have been ultimated. The mass of observations of _Saturn_, of _Jupiter_, of _Mars_, of _Venus_, would have been made and published. The researches on the sun, on the "invisible rays" of heat, on comets and nebulæ--all these might have been made, printed, and read.