Page:Dictionary of National Biography, Second Supplement, volume 1.djvu/418

 1876, and in January 1878 contributed to the society's 'Monthly Notices' a note on the satellites of Mars and Saturn, depending on observations made with a silver- on-glass mirror of 18 inches diameter made by Mr. Calver. With this type of astronomical instrument the name of Common will be always associated. A note on large telescopes, and a suggestion of the desirability of photographing the planets Saturn and Mars (Monthly Notices, March 1879) indicated his foresight as a practical astronomer, before large telescopes and photography were in general use. Insisting on the superior merits of silver-on-glass mirrors over metal specula, he mounted a silver-on-glass mirror of 3 feet diameter, obtained from Mr. Calver ; adopting a plan of his own, he supported the weight of the instrument by partially floating the polar axis in mercury, and with this instrument Common made experiments in astronomical photography which were subsequently acknowledged to have opened a new field for astronomers. With this 3-foot mirror Common was able after much experimental work to photograph on 24 June 1881 the great comet of that year, the first successful photograph on record of a comet, though a second was obtained on the same night by Dr. Draper, in America. On 17 March 1882 Common photographed the great nebula in Orion. After some improvement of his instrument and further trials, a more successful photograph of the same object was obtained on 30 Jan. 1883. By way of recognition of this pioneer work in a branch of astronomy now very much practised, the gold medal of the Royal Astronomical Society was awarded to Common in February 1884. The 3-foot mirror was ultimately sold to Mr. Crossley of Halifax, who presented it to the Lick Observatory, where, after refiguring and alterations, it is in efficient use.

The successful performance of the 18-inch and the 3-foot silver-on-glass mirror induced Common to attempt the construction of a larger telescope of the same kind. With characteristic confidence he made his first essay in mirror-grinding with a disc of 5 feet diameter, which was begun in the workshop adjoining his house at Baling in 1886, and after five years of hard work and anxious experiment, a successful 5-foot equatorial reflecting telescope was completed (see memoir presented to Royal Astron. Soc. 11 Dec. 1891). Common made little use personally of this telescope, which is now in the Harvard College Observatory, U.S.A. Subsequently Common found the construction of small mirrors an easy task, and of these he made many. He generously presented to the Royal Society mirrors for observing eclipses. He not only made the plane mirror but constructed the mechanical parts of coelostats for use by the official expeditions for the solar eclipse of 1896, while 30-inch mirrors now at the Solar Physics Observatory, South Kensington, at the Khedivial Observatory, Helwan, and one which forms part of the Thompson equatorial at Greenwich, were all from his workshop. There are also smaller flat mirrors by him at the National Physical Laboratory and at the Cambridge University Observatory.

Apart from his mechanical skill, Common made various noteworthy observations. Specially memorable is his observation in daylight on 17 Sept. 1882 of the great comet of that year, when it was quite close to the sun. Common was unaware of an earlier discovery of this comet in the southern hemisphere, when he made his observations in accordance with a plan of searching for comets near the sun that he had been following for some time.

Common was somewhat distracted in later years from scientific pursuits by his association with the British Aluminium Company, of which he was one of the first directors, and in connection with this he was interested in the adaptation of the water power of the Falls of Foyer in Scotland. After severing connection with this enterprise he invented a telescopic gun-sight for use in the army and navy, working out a suggestion which he had read in youth in an early manual on astronomy. His telescopic gun-sight, when properly used, has been estimated as quadrupling the fighting efficiency of battleships.

Common was elected a fellow of the Royal Society in 1885, and served on its council in 1893-5. He was treasurer of the Royal Astronomical Society from 1884 to 1895, and its president from 1895 to 1897. In 1891 he was made hon. LL.D. of St. Andrews. He was a member of the board of visitors of the Royal Observatory, Greenwich, from 1894 until his death. In 1900, as president of the astronomical section at the British Association, he delivered an address on the development of astronomical instruments and the application of photography to astronomy. For some years he was joint editor with Professor H. H. Turner of the 'Observatory Magazine.' Of resolute temperament, and strong both physically and intellectually, Common was a clubbable man with many friends.