Astronomical equipment, sun diagonal, Herschel Wedge, metal / glass, made by John Browning, London, England, 1875-1900, used at Sydney Observatory, New South Wales, Australia, [1900-1950]
This sun diagonal was used at Sydney Observatory as part of a major international project aimed at mapping the stars. A sun diagonal is a device that allows users to directly view the sun in white light without causing injury to their eyes. The prism reflects only a small percentage of the sun's light up through the eyepiece. Around 95 % of the light and heat are directed out through the bottom of the device.
The sun diagonal is commonly known as a 'Herschel Wedge'. William Hershel (1738-1822) was famous for discovering Uranus, infrared radiation and numerous other discoveries in astronomy. The Powerhouse Museum has one of Herschel's speculum mirrors in its collection (H10259).
This particular sun diagonal was adapted to be used with the guiding telescope H10374. This guiding telescope was rigidly fixed to the Sydney Astrographic Telescope, H10255, which was used in the Mapping the Stars project. In 1887 astronomers from around the world embarked on a massive new enterprise; known as the Carte du Ciel (Mapping the Stars) project, it involved photographing and measuring the stars in both hemispheres. Australia was actively involved in the project with observatories in Sydney, Melbourne, and Perth keen to participate in this international project. Each observatory was allocated a zone of the sky and was expected to record it using instruments of a standard pattern.
Only parts of the Sydney astrograph instrument remain, but they are significant for the role they played in the international project and the fact that they were once part of one of the earliest astrographs constructed in Australia.
The sun diagonal was also used at Sydney Observatory to observe a transit of Mercury in the 1940s. Mercury and Venus are the only two planets to transit the sun. The transit of Mercury occurs about 13 to 14 times every century and can be viewed when the planet travels between the sun and the observer.
This sun diagonal remains of national significance due to its pioneering role in Australian science and its association with Australia's earliest astronomers and astronomical equipment. It is also of international significance due to its association with nineteenth century scientific instruments and their makers.
Russell, H. C., Description of the Star Camera at The Sydney Observatory, Alfred James Kent, Government Printer, 1923, p.4
King, H., C., The History of the Telescope, Dover Publications, New York, 1955, p.300
Glass, I. S., Victorian Telescope Makers; the Lives and Letters of Thomas and Howard Grubb, Institute of Physics Publishing, Bristol and Philadelphia, 1997
Written by Erika Dicker
Assistant curator, February 2008.
The sun diagonal was made circa 1880 by instrument maker John Browning of 68, The Strand, London, England.
John Browning (1835-1925) was a significant maker of scientific instruments in the 19th century. His father, William Browning, had been manufacturing scientific instruments since the late 1700s and John joined him when he came of age. John Browning took over sole ownership of this business in 1856.
Between 1856 and 1872 he acquired provisional patents for numerous instrument designs and received a prize at the 1862 International Exhibition in London for his temperature compensated aneroid barometer. He was also a keen astronomer and set about manufacturing affordable reflecting telescopes. He gained wide repute among the ophthalmic surgeons in London for his instruments.
He was specifically known as one of the 19th century's leading designers and manufacturers of spectroscopes. It is recorded that Browning was not satisfied with his products until he had confirmation from the customer that the instrument worked perfectly. He provided a custom-made spectroscope for famous photographer William Henry Fox Talbot (1800-1877) in 1865 . He also published the book 'How to Work with the Spectroscope' in 1878.
He was a member of several scientific groups such as The Microscopical Society of London, The Meteorological Society, The Royal Institution, and The Royal Astronomical Society.
Browning instruments were manufactured at 111 Minories in London from around 1765 until 1872. In 1872 the company moved premises to 63 Strand in London, and it was also recorded to have had a workshop at 6 Vine St, London.
John Browning Obituary, Monthly notices of the Royal Astronomical Society, Vol XC, No4, February, 1930
Webster's signature database.
Written by Erika Dicker
Assistant Curator, February, 2008.