a fresh small world or two every year, and we have even had another large planet (Neptune), still more remote than Herschel’s Uranus, added to the list of known orbs in our own solar system.  But in Herschel’s day, nobody had ever heard of a new planet being discovered since the beginning of all things.  A hundred years before, an Italian astronomer, it is true, had found out four small moons revolving round Saturn, besides the big moon then already known; but for a whole century, everybody believed that the solar system was now quite fully explored, and that nothing fresh could be discovered about it.  Hence Herschel’s observation produced a very different effect from, say, the discovery of the two moons which revolve round Mars, in our own day.  Even people who felt no interest in astronomy were aroused to attention.  Mr. Herschel’s new planet became the talk of the town and the subject of much admiring discussion in the London newspapers.  Strange, indeed, that an amateur astronomer of Bath, a mere German music-master, should have hit upon a planet which escaped the sight even of the king’s own Astronomer Royal at Greenwich.

Of course there were not people wanting who ascribed this wonderful discovery of Herschel’s to pure chance.  If he hadn’t just happened to turn his telescope in that particular direction on that particular night, he wouldn’t have seen this Georgium Sidus they made such a fuss about at all.  Quite so.  And if he hadn’t built a twenty-foot telescope for himself, he wouldn’t have turned it anywhere at any time.  But Herschel himself knew better.  “This was by no means the result of chance,” he said; “but a simple consequence of the position of the planet on that particular evening, since it occupied precisely that spot in the heavens which came in the order of the minute observations that I had previously mapped out for myself.  Had I not seen it just when I did, I must inevitably have come upon it soon after, since my telescope was so perfect that I was able to distinguish it from a fixed star in the first minute of observation.”  Indeed, when once Herschel’s twenty-foot telescope was made, he could not well have failed in the long run to discover Uranus, as his own description of his method clearly shows.  “When I had carefully and thoroughly perfected the great instrument in all its parts,” he says, “I made a systematic use of it in my observation of the heaven, first forming a determination never to pass by any, the smallest, portion of them without due investigation.  This habit, persisted in, led to the discovery of the new planet (Georgium Sidus).”  As well might one say that a skilled mining surveyor, digging for coal, came upon the seam by chance, as ascribe to chance the necessary result of such a careful and methodical scrutiny as this.