Sir Frederick William Herschel

HERSCHEL, SIR FREDERICK WILLIAM (1738 182 2 ), generally known as Sir William Herschel, English astrono mer, was born at Hanover on Nov. 15, 1738. His father was a musician in the Hanoverian guard, and in 1757 Herschel was sent to England to earn his living as a musician.

Beginnings.

In 1766 he worked as organist in Bath. During the next five or six years he became the leading musical authority. In 1772 he revisited Hanover to bring back with him his sister Caroline, whose services he much needed, as he was already study ing astronomy in the time he could spare from his musical engage ments. She thus describes her brother's life soon after her arrival : "He used to retire to bed with a bason of milk or a glass of water, with Smith's Harmonics and Ferguson's Astronomy, etc., and so went to sleep buried under his favourite authors; and his first thoughts on waking were how to obtain instruments for viewing those objects himself of which he had been reading." It was in this way that he was introduced to the writings of Ferguson and Keill, and subsequently to those of Lalande, whereby he educated himself to become an astronomer of undying fame.

In those days telescopes were rare, very expensive and not very efficient, and Herschel used a small Gregorian reflector of about 2 in. aperture. Finding it impossible to obtain a reflector of larger dimensions, he decided to construct his own and, in 1774 had the satisfaction of viewing the heavens with a Newtonian telescope of 6 ft. focal length made by his own hands. He had from the very first conceived the gigantic project of surveying the entire heavens, and, if possible, of ascertaining the plan of their general structure. For this he required adequate instruments, and he, his brother and his sister toiled at the grinding and polish ing of hundreds of specula. After 1774 every available hour of the night was devoted to the long-hoped-for scrutiny of the skies.

In May 1780 his first two papers on the variable star "Mira" and the mountains of the moon were communicated to the Royal Society.

The phenomena of variable stars were examined by Herschel as a guide to what might be occurring in our own sun, and the results of his investigations were communicated to the Royal Society in six memoirs (see Phil. Trans., 1780-1801). It was in 1801 that these remarkable papers culminated in the enquiry whether any relation could be traced in the recurrence of sun spots, regarded as evidences of solar activity, and the varying seasons of our planet, as exhibited by the varying price of corn.

The Rotation of Planets.

In 1781 he communicated to the Royal Society the first of a series of papers on the rotation of the planets and of their several satellites. These enquiries occupy the greater part of seven memoirs extending from 1781-97. While engaged on them he noticed the curious appearance of a white spot near to each of the poles of the planet Mars. On investigat ing the inclination of its axis to the plane of its orbit, and finding that it differed little from that of the earth, he concluded that its changes of climate also would resemble our own, and that these white patches were probably polar snow. He also discovered that the times of the rotations of the various satellites round their axes conform to the analogy of our moon by equalling the times of their revolution round their primaries.

In the same year (1781) Herschel made a discovery which completely altered the character of his professional life. In the course of a methodical review of the heavens he lighted on an object which averred itself to be a new planet, moving outside the orbit of Saturn. He assigned to it the name Georgium Sidus, but this has been laid aside in favour of Uranus. The object was detected with a 7-ft. reflector having an aperture of 61 in. Seven memoirs on the subject were communicated by him to the Royal Society, extending from the date of the discovery, in 1781-1815.

For the discovery of the planet he was awarded the Copley medal of the Royal Society, elected a fellow, and in the following year, 1782, he accepted George III.'s offer to give up music and become his private astronomer. So Herschel and his sister moved first to Datchet and in 1786 to Slough. Here he resumed his astronomical pursuits with extraordinary vigour, although for a time he had to supplement his income by making and selling telescopes. The necessity for this interruption in his observations was overcome in 1788 when he married the wealthy widow of a London merchant.

Double Stars.

A material part of the task that Herschel had set himself embraced the determination of the relative distances of the stars from our sun and from each other. This resulted in a most important series of observations. He had observed many stars in apparently very close contiguity, but often differing greatly in relative brightness. He concluded that, on the average, the brighter star would be the nearer to us, the fainter enormously more distant.

In the hope, therefore, of detecting an annual parallactic dis placement of one star with respect to another, he mapped down the places and aspects of all the double stars that he met with, and communicated in 1782 and 1785 very extensive catalogues of the results. His last scientific memoir, sent to the Royal Astronomical Society in 1822, when he was its first president and already in his 84th year, related to these investigations. In the memoir of 1782 he threw out the hint that these apparently contiguous stars might be genuine pairs in mutual revolution. Eleven years afterwards ), he remeasured the relative positions of many such couples and his prediction was verified, for he ascertained that some of these stars circulated round each other, after the manner re quired by the laws of gravitation. This discovery, announced in 1802, would of itself suffice to immortalize his memory.

In 1783 he wrote his first memorable paper on the "Motion of the Solar System in Space"—a sublime speculation, yet through his genius realized by considerations of the utmost simplicity. He returned to the same subject with fuller details in 1805. In a series of papers, extending from the year 1784-1818, he used his method of star gauging and concluded that our sun was a star situated not far from the bifurcation of the Milky Way, and that all the stars visible to us lie more or less in clusters scattered throughout a comparatively thin, but immensely extended stratum. Oa either side of this assemblage of stars, Herschel discovered a canopy of discrete nebulous masses, such as those from the con densation of which he supposed the whole stellar universe to have been formed.

Hitherto we have said nothing about his construction of the great reflecting telescope, of 4o ft. focal length and 4 ft. aperture. The full description of this celebrated instrument will be found in the 85th volume of the Transactions of the Royal Society. On the day that it was finished (Aug. 28, 1789) Herschel saw at the first view, in a grandeur not witnessed before, the Saturnian system with six satellites, five of which had been discovered long before, while the sixth he had glimpsed two years before, in his exquisite little telescope of 64 in. aperture, but now saw in un mistakable brightness. On Sept. 17 he discovered a seventh, which proved to be the nearest to the globe of Saturn.

Herschel died at Slough on Aug. 25, 1822, a description of him given a few years before by Campbell being—"A great, simple, good old man. His simplicity, his kindness, his anecdotes, his readiness to explain his own sublime conceptions of the universe, are indescribably charming." See Mrs. John Herschel, Memoir of Caroline Herschel (1876) ; E. S. Holden, Herschel, his Life and Works 0880 ; A. M. Clerke, The Herschels and Modern Astronomy (1895) ; E. S. Holden and C. S. Hastings, Synopsis of the Scientific Writings of Sir William Herschel (Washington, 1880 ; Baron Laurier, doge historique, Paris Memoirs (1823),'p. ixi.; F. Arago, Analyse historique, Annuaire du Bureau des Longitudes (1842) , p. 249 ; Arago, Biographies of Scientific Men, p. 167 ; Madame d'Arblay's passim; Public Characters (I , P. (with portrait) ; J. Sime, William Herschel and his Work (iqoo). Herschel's photometric Star Catalogues were discussed and reduced by E. C. Pickering in Harvard Annals, vols. xiv. p. 345, xxiii., and xxiv.