British Astronomical Association

Instruments 

The Association owns about 200 instruments for loan to members, although the majority of them are currently in use. Application for loan is to be made to the Curator of Instruments, and must be supported by a Section Director or by a member of at least five years' standing. Preference is given to those who intend to participate, or who are already participating, in the work of the Observing Sections, and normally few items are available for beginners.

Purchase of equipment

The Association does not recommend or endorse any specific make of telescope or other equipment, but enquiries can be passed to members who can provide advice about choosing and purchasing wisely.

Further Details of The Instrument Collection
R.A. Marriott, Curator

When the Association was founded in 1890 there were no immediate thoughts about forming an instrument collection, which ten years later consisted of only six instruments: a diffraction grating (No.1) presented by John Brashear in 1890, a 4-inch photographic refractor (No.2) presented by G.E. Niblett in 1895, an 18-inch reflector with optics by G.H. With (No.3) presented by N.E. Green (then President) in 1897, a 2-inch transit instrument (No.4) presented by Tyson Crawford (senior partner at Dollond's) in 1897, a 3-inch refractor (No.5) presented by G.T. Davis in 1899, and a 3.5-inch refractor by Wray (No.6) bequeathed by Elizabeth Brown in 1899.

By 1940 the number of instruments in the collection had risen to 78, only 1 of which had been purchased, the rest having accrued from presentations or bequests. To date the number of instruments acquired - telescopes, mirrors, OGs, cameras, photographic lenses, micrometers, spectroscopes, measuring machines, radio equipment, microscopes and numerous peripherals - totals 457, although less than half of these remain in the collection, the rest having been sold because of antique value, or written off due to obsolescence, excessive damage or loss (by borrowers), or simple inadequacy. Some indeed, have met dramatic ends: one was abandoned in Russia after the aborted eclipse expedition of 1914, and another was destroyed during the Blitz in 1941.

The term 'instrument' can of course be applied to any piece of equipment; even eyepieces have been presented, but without doubt the largest instrument to be acquired was the 9-inch folded refractor with a 10-inch plane (No.96), custom-built by Cooke for William Strachan in the 1920s and presented to the Association by A.M. Newbegin in 1947. But even this would have been dwarfed by the 15-inch Grubb refractor (now at Alston Hall, Preston) bequeathed by Wilfred Hall in 1953. A condition of Hall's bequest, however, was that an observatory should be built to contain it, and as this was beyond the means of the Association the bequest passed to the Royal Astronomical Society.

The collection continues to change, and more than 50 items have been added since the appointment of the present Curator in 1991.

Historical Notes on Selected Instruments

Instrument No.188 : 6-inch Grubb refractor
Presented by the Royal Astronomical Society, 1956

The late Harold Ridley's observatory at East Chinnock, near Yeovil. The guidescope is a 6-inch Grubb refractor, originally presented by the British Transit of Venus Committee to the Royal Astronomical Society (registered as RAS Instrument No.123) to replace RAS 29 (Sheepshanks 3), a 4.6-inch achromat lost at sea after the Transit of Venus Expedition of 1882.

During the nineteenth century RAS instruments were loaned to Fellows, and in 1885 the 6-inch Grubb was placed on loan to Lord McLaren (1831-1910), a Scottish Law Lord, created Lord Advocate by Gladstone in 1880. McLaren served as Vice-President of the Royal Society of Edinburgh for many years, was Director of Ben Nevis Observatory, and with the Earl of Crawford and Ralph Copeland was instrumental in the establishment of the Royal Observatory at Blackford Hill. Among his own instruments was a 4-inch heliometer which David Gill used to observe Mars from Ascension Island in 1877.

From 1888 to 1890 the Grubb was on loan to Alexander Freeman (1839-1897) - an Original Member of the BAA and Director of the Saturn Section from 1893 to 1895 - and after its return it was loaned to William E. Wilson (1851-1908), of Daramona, Streete, Co. Westmeath. Some years earlier Wilson had established a physical laboratory and an observatory equipped first with a 12-inch reflector and, in 1881, a 24-inch reflector. He carried out much research into thermal radiation, particularly relating to the Sun, and also undertook investigations in photometry, spectroscopy and photography. In 1891 he mounted the Grubb as a guidescope on his 24-inch reflector, which he had just had remounted (with electric drive) by Grubb, and in 1900 it was temporarily removed from the 24-inch and taken to Plasencia, Spain, where, in conjunction with a Grubb coelostat loaned by the Royal Dublin Society, it was used to photograph the total solar eclipse of May 28. Wilson's last few years were devoted almost exclusively to laboratory work, as during the period 1901-08 the rain fell on Daramona for an average of 250 days per year, the annual rainfall approaching 50 inches. In 1925 his son F.G. Wilson presented the 24-inch reflector to the University of London, a gesture commemmorated by the University's appointment of the Wilson Lecturer; it was the first instrument to be installed at Mill Hill Observatory, which opened in 1929.

In 1956 the RAS presented several instruments to the Association, including this 6-inch Grubb. For a few years it was with E.J. Hysom, and in 1967 was placed on loan to Harold Ridley, who used it as a guidescope on an astrograph equipped with a 49-inch focus f/7 Zeiss triplet, a lens now mounted on the Mond astrograph originally installed at the Norman Lockyer Observatory (formerly the Hill Observatory), and now in the possession of Glyn Marsh.

Instrument No.131 : 6-inch modified short-focus Cassegrain reflector by Dall
Bequeathed by the Rev. M.P.M. McLean, 1949

The prototype Dall-Kirkham, first described and exhibited by Horace Dall at the Association's meeting of 29 June 1932: "Mr. H.E. Dall then described a 6-inch reflector of Cassegrain type, constructed chiefly for terrestrial use, which he had brought with him to the meeting. In answer to a question, he stated that the loss of light as compared with a Newtonian of the same aperture, due to the tiple achromatic lens in the optical system, was not more than about 10 per cent. Instr.-Capt. Ainslie said that he would like to congratulate Mr. Dall on the design of his telescope, and also on its execution. Mr. Dall's optical system obviated two at least of the well-known disadvantages of the Cassegrain; in the first place, it enabled the ratio of equivalent focal length to aperture to be kept within reasonable bounds, that of Mr. Dall's telescope being 15 to 1; in this way it was possible to use eyepieces of normal focal lengths, as with an ordinary refractor, and a low power could be obtained without an unduly small field of view. Then again, it was a great advantage to have the 'sky-stop', which was necessary in the Cassegrain, and so difficult to fit - especially with high-power eyepieces, in its usual position outside the latter - of a large size and a constant aperture for all powers, as well as being within the system at a point where it caused discomfort, instead of between the eye and the eyepiece. He would also like to draw the attention of members to the fact that the aperture ratio of the large speculum was only 3.2 to 1: this meant considerable difficulty in figuring, and the fact that Mr. Dall had been able to do it argued very high skill on his part; he (the speaker) knew from experience the difficulty of figuring a mirror ratio of 7 to 1, and Mr. Dall had done something far more difficult. With regard to the erect image, at first sight this appeared at a disadvantage, as we were so accustomed to the inverted image, both in the telescope and in drawings of the moon and planets; but he ventured to suggest that this might be really an advantage, especially for planetary and lunar work, as presenting to the eye an unfamiliar view, and avoiding any suggestions of bias... Mr. Dall's telescope was certainly the most compact he had ever seen of its aperture; and the fact that the weight had been kept down to something like 5.5 pounds for a 6-inch aperture was, in itself, a very remarkable feat."

From 1965 to 1993 the instrument was on loan to G.C.I. Rawlings, who used it chiefly for TLP work.

Enquiries

Any queries  to the Curator of Instruments, Bob Marriot, e-mail ram@hamal.demon.co.uk