Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/805

HERSCHEL 769 chair of chemistry in that university ; but, as he said with some humour, the result of the election was that of the votes he had a glorious minority of one. In fact Herschel had become an astronomer from a sense of duty, just as his father had become one by fascination and fixed resolve ; hence it was by filial loyalty to his father s memory that he was now impelled to undertake the com pletion of that work which at Slough had been so grandly commenced. William Herschel had explored the northern heavens ; John Herschel determined to explore the heavens of the south, as well as re-explore the north. " I resolved," he said, " to attempt the completion of a survey of the whole surface .of the heavens ; and for this purpose to transport into the other hemisphere the same instrument which had been employed in this, so as to give a unity to the results of both portions of the survey, and to render them comparable with each other." In accordance with this resolution, he and his family embarked for the Cape on the 13th November 1833; they arrived in Table Bay on the 15th January 1834 ; and proceedings, he says, "were pushed forward with such effect that on the 22d of Feb ruary I was enabled to gratify my curiosity by a view of K Crucis, ths nebula about 77 Argus, and some other remarkable objects in the 20-foot reflector, and on the night of the 4th of March to commence a regular course of sweeping." To give an adequate description of the vast mass of labour com pleted during the next four busy years of his life at Feldhausen would require the transcription of a considerable portion of the Cape Observations, a volume which probably is not surpassed in varied interest or astronomical importance by any scientific work in existence ; although it might perhaps be equalled by a judicious selec tion from Sir William s " Memoirs," now scattered in some thirty volumes of the Philosophical Transactions. It was published, at the sole expense of the late duke of Northumberland, but not till 1847, nine years after the author s return to England, for the very cogent reasons assigned by himself : "The whole of the observa tions, as well as the entire work of reducing, arranging, and pre paring them for the press, have been executed by myself." There are 164 pages of catalogues of southern nebulae and clusters of stars. There are then careful and elaborate drawings of the southern appearance of the great nebula in Orion, and of the region surround ing the remarkable star of Argo. The labour and the thought bestowed upon some of these objects are almost incredible ; several months were well spent upon a minute spot in the heavens contain ing 1216 stars, but which an ordinary spangle, held at a distance of an arm s length, would eclipse. These catalogues and charts being completed, he proceeds to discuss their significance, which in the eyes of science possesses an absorbing interest. He confirms his lather s hypothesis that these wonderful masses of glowing vapours are not irregularly scattered, and without apparent law, hither and thither in the visible heavens, but are collected in a sort of canopy, whose vertex is at the pole of that vast stratum of stars in which our solar system finds its position, buried in it, as he supposes, at a depth not greater than that of the average distance from us of an eleventh magnitude star. Then follows his catalogue of the relative positions and magnitudes of the southern double stars. And he applies to one of them, 7 Yirginis, that beautiful graphical method invented by himself, whereby he determines the orbit of the two components round each other ; and he had the satisfaction of wit nessing with his own eyes the fulfilment of a prediction he had made some years before, viz., that the two stars would, in the course of their orbital movements, appear to close up into a single star, in separable by any telescopic power. The double stars and their stately revolutions and lustrous colours dismissed, in the next chapter he proceeds to describe the observations which he had made on their varying and relative brightness. It has been already detailed how his father commenced his scientific career by similar observations on the varying magnitudes of many stars, and how his remarks culminated years afterwards in the question whether the variation of the lustre of our sun, by the presence or absence of sun spots, affected pur harvests and the price of corn. The son carries his speculations backwards to a still more philosophical depth. The variation from time to time, he remarks, in the lustre of our sun, to the extent of half a magnitude, would account for those strange alternations of a semi-arctic and semi-tropical climate which geo logical researches have disclosed as having occurred in various regions of our globe. Herschel returned to his English home in the spring of 1838. As was natural and honourable to all concerned, he was welcomed with an enthusiastic greeting. By the queen at her coronation he was created a baronet ; and, what to him was better than all such rewards, other men caught the contagion of his example, and laboured in fields similar to his own, with an adequate portion of his success. In particular Mr Lassell transported a telescope as large as the celebrated Herschelian telescope to Malta, where with excellent results he "minded the heavens" for the space of four years. He was rewarded there, and at his own English residence near Liverpool, by the discovery of new satellites of Saturn and of Uranus, constituting what Sir John Herschel, animated by a fraternal sympathy, well called an epoch in astronomy. Mr De La Rue also, at Islington and at Cranford, followed zealously and successfully in the wake of the same infec tious enthusiasm. Herschel was a highly accomplished chemist. His dis covery of the solvent power of hyposulphite of soda on the otherwise insoluble salts of silver, in 1819, exercised a most important influence on the practical applications of photography twenty years afterwards; and in 1839, the natal era of that valuable art, he, independently of Mr Fox Talbot, had discovered the means of taking and multiplying photographic pictures, and early in the spring of that year exhibited more than twenty photographic pictures to the Iloyal Society, including one of the old 40-foot telescope. He was the first person to introduce the now well-known terms positive and negative in photographic images, and to dsposit upon glass a sensitized film for the reception of the picture. He also paved the way for Professor Stokes s im portant discovery of the change which luminous waves may suffer in their period of oscillation, by his addition of the lavender rays to the spectrum, and by his announcement of "epipolic dispersion," as exhibited by sulphate of quinine. Several other important and successful researches of his, connected with the undulatory theory of light, are scattered through the pages of his treatise on " Light " published in the Encyclopedia Metropolitana. To the other varied accomplishments of his gifted mind we must add the graces of a deep poetic feeling. Perhaps no man can become a truly great mathematician or great philosopher, if unendowed with the versatile powers of the imagination. John Herschel possessed this endowment to a large extent ; and he had reserved for himself as a solace and enjoyment in old age the translation of the Iliad into verse. He had at an earlier period of life translated in a similar manner Schiller s Walk. But the main work of his declining years was the collection of all his father s cata logues, combined with his own observations and those of other astronomers of nebulae and double stars, each into a single volume. He lived to complete the former, and to present it to the Iloyal Society, who have published it in a separate form in the Philosophical Transactions, The latter work he had not fully completed at his death ; but he bequeathed as much of it as was finished to the Astro nomical Society. That society has printed a portion of it, which serves as an index to the observations of various astronomers on double stars up to the year 1866. A complete list of his various contributions to learned societies will be found in the Royal Society s great cata logue, and from them may be gathered most of the records of his busy scientific life. Sir John Herschel met with an amount of public recognition which was unusual in the time of his illustrious father. Naturally he was a member of almost every important learned society in both hemi spheres. For five years he held the office of master of the mint, the same appointment which, more than a century before, had been occupied by Sir Isaac Newton ; his friends also offered to propose him as president of the Royal Society and again as a member of parliament for the uni versity of Cambridge, but neither office was within the scope of his own desires.

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