these two appear as one star. With a telescope this is seen to be two stars, some 5″ apart. In the whole sky there are not above fifty such stars as the brighter of the two, and about four hundred of the brilliancy of B. These fifty and four hundred stars are scattered over the vault of heaven, almost at random. No law has yet been traced by which we can say that here or here there shall be a bright star like A, or a fainter one like B. In general the distribution appears to be fortuitous. How then can we account for one of the four hundred stars like B placed so close to one of the fifty like A?
The chances are over four hundred thousand to one that the association in position is not accidental. This argument becomes overwhelming when the same association is found in many other cases. There were two hundred and three doubles in the Catalogue of 1782 alone, and many thousands are now known.
By a process like this, Herschel reached his grand discovery of true binary systems, where one sun revolves about another. For
