tracts of luminous matter: their real nature was not suspected. But as soon as Herschel applied to them his powerful instruments, his rare penetration and unconquerable perseverance, this branch of science took a rapid stride. In 1796 he published in the "Philosophical Transactions" a catalogue of one thousand nebulæ or clusters of stars. Three years later appeared a second catalogue, quite as extensive as the first; and that, again, was followed, in 1802, by a third catalogue of five hundred nebulæ.
"Two thousand five hundred nebulæ!" exclaims Arago; such was the contingent supplied by Herschel to a branch of astronomy which had hardly been touched before him. But he was not content with simple discovery. It was his rare good fortune to demonstrate their true nature.
One single nebula out of the vast "contingent" mentioned by Arago, resolved itself under Herschel's telescope into a cluster of fourteen thousand stars! And though not all the nebulæ are resolvable into similar clusters, it is demonstrated by his, and by subsequent observations, that thousands of these beautiful objects are clusters of innumerable stars, so immeasurably distant from us that only their collective light is visible—a dimly luminous point in boundless space.
The immense distance of the planet Uranus, its small angular diameter, and the feebleness of its light, long forbade any hope of discerning from the earth its satellites, if any such existed. It was to the great forty-feet telescope, invented and built by Herschel, that the discovery was due at last. His perseverance was rewarded by a sight of six moons, which revolve around the planet, thus completing, to use the words of Arago, "the world of a system that belongs entirely to himself."
Time went on in the Slough observatory unmarked by any incident external to the scientific labours of its inmates, if we except the birth of his son, Sir John Herschel. Their work, their pleasures, and the events of their lives, were all astronomical. Sir William's position as astronomer to the king brought a constant succession of guests to the observatory who were distinguished by their rank, and his own eminence in science attracted those who were best worth knowing in the world of letters, whether Englishmen or foreigners. Miss Herschel, who liked a quiet joke as well as any one, tells some good stories of her visitors. Some of them, it must be acknowledged, asked very remarkable questions; amongst others, one is recorded of the Prince of Orange, who called one day at the observatory to see Sir William Herschel, but, not finding any one at home, wrote the following note: —
The Prince of Orange has been at Slough to call at Mr. Herschel's, and to ask him, or if he was not at home, to Miss Herschel, if it is true that Mr. Herschel has discovered a new star whose light was not as that of the common stars, but with swallow-tails as stars in embroidery.
About the time when Sir John Herschel, having arrived at man's estate, took his degree as senior wrangler, Sir William's health began to fail. He still pursued his labours, but no longer with his wonted energy, and the journals are filled with remarks which show the bitter grief with which Miss Herschel noted his declining strength. He died in 1822, in the seventy-second year of his age.
The terrible blow of her brother's death seemed to paralyze the energies of his sister, who determined to leave England forever, as soon as the beloved remains were buried out of her sight. She collected the few things which she desired to keep, and retired to Hanover. Her letters from thence to her nephew, Sir John Herschel, are full of recollections of the past, and abound with anecdotes of the great astronomer with whom she passed so many years.
The reader of the memoir will be well able to appreciate the efficient service which Miss Herschel gave to her brother during the forty years of his astronomical work; but she herself did not think so. She always said that a well-trained puppy-dog would have done for her brother everything that she had done; that she was a tool fashioned and polished by him; and that if the tool performed anything worth doing, he was entitled to the credit of it. Thinking nothing of herself, seeking nothing for herself, with an intense power of sympathy, and a noble love of giving herself for the service of others, she transferred her whole personality to the object of her affection. After her brother's death she transferred that affection to his son; she often said that she would have willingly remained at the old observatory at Slough to work under the son, as she had done under the father, but that her strength and health would no longer serve her.
It is sad to think of her in her old age. She was then seventy-two, going back des-
