Page:Hector Macpherson - Herschel (1919).djvu/61



did not attain to the knowledge of the ultimate structure of the Universe to which he aspired; but in the course of his long career as an observer and thinker he was led to several discoveries of the greatest importance. The discovery of nebulæ was, of course, one of the objects of his long-continued series of "sweeps" of the heavens. He communicated his first catalogue of 1000 new nebulæ and clusters of stars to the Royal Society in 1788; this was followed three years later by a second catalogue of 1000 similar objects, while in 1802 he drew up a catalogue of 500 "new nebulæ, nebulous stars, planetary nebulae and clusters of stars". He was equally devoted to the study of double stars. These objects, as already mentioned, first attracted his attention because of their suitability for determination of relative stellar parallaxes. But Herschel soon realised that the measurement of the annual parallax of stars was beyond the power of his instruments. His quest for parallaxes from the study of double stars led him to another discovery altogether.

On 10th January, 1782, he communicated to the Royal Society a catalogue of 269 double stars, of which 227 had been discovered by himself; this was succeeded by a second list of 434 in December, 1784. From the beginning of his study of these stellar pairs, he seems to have had a suspicion as to their nature. In the postscript to his first catalogue he said: "In my opinion, it