Common, Andrew Ainslie

(b. Newcastle-upon-Tyne, England, 7 August 1841; d. Ealing, London, England, 2 June 1903),

astronomy

Common was noted for his pioneer work in celestial photography and in the design and construction of large telescopes. His professional work as a sanitary engineer prevented his having sufficient time to pursue astronomy effectively until 1875, when he began to experiment with taking photographs through a telescope. The next year he constructed a thirty-sixinch silver-on-glass reflector, with a mirror made by George Calver and a mounting of his own design; the main moving part (the polar axis) floated on mercury to reduce friction. By devising a photographic plate holder that could be moved during exposure to counteract errors in the clock drive of the telescope, Common was the first to make really long exposures successfully. He took the first satisfactory pictures of Jupiter and Saturn and, in 1883, a superb picture of the nebula in Orion that showed the superiority of a photograph over a drawing.

For astronomical colleagues Common constructed many large parabolic mirrors between thirty and sixty inches in diameter and high-quality flat mirrors; in the latter work he was aided by a very sensitive spherometer of his own design. His largest telescope was a sixty-inch reflector, with the polar axis floating in water. Many difficulties attended its construction, and it was not ready for use until 1889. Common had by then become involved in designing gunsights for the Royal Navy—a contemporary claimed these were so successful that they quadrupled fighting efficiency—and this work prevented Common from using his new instrument before his sudden death. The excellent thirty-six-inch reflector was sold to Edward Crossley of Halifax, England, and presented by him to Lick Observatory, where it was used for photography with great success by James Keeler and others from 1898 to 1900.

Common was awarded the Gold Medal of the Royal Astronomical Society in 1884, was its president from 1885 to 1887, and was elected a fellow of the Royal Society in 1885.

BIBLIOGRAPHY

Significant papers by Common, all in Monthly Notices of the Royal Astronomical Society, are “Note on Large Telescopes, With Suggestions for Mounting Reflectors,” 39 (1879), 382–386; “Note on Silvering of Large Mirrors,” 42 (1982), 77–78; “Note on a Photograph of the Great Nebula in Orion and Some New Stars Near Orionis,” 43 (1883), 255–257; “Suggestions for Improvements in the Construction of Large Transit Circles,” 44 (1884), 288–293; “Note on a Method of Reducing the Friction of the Polar Axis of a Large Telescope,” ibid., 366–367; “Note on Stellar Photography,” 45 (1885), 25–27; and “Note on an Apparatus for Correcting the Driving of the Motor Clocks of Large Equatorials for Long Photographic Exposures,” 49 (1889), 297–300.

A print of a photograph of Jupiter appears in Observatory, 3 (1880), pl. III; prints of photographs of Jupiter, Saturn, and the Orion nebula are on the frontispiece and the title page of A. M. Clerke, A Popular History of Astronomy During the Nineteenth Century (London, 1893).

Obituaries of Common are in Monthly Notices of the Royal Astronomical Society, 64 (1904), 274–278; and Proceedings of the Royal Society, 75 (1905), 313–318.

Cotin A. Ronan