F.M. Holborn’s observatory

Streatham, London

Journal of the British Astronomical Association, 50 (9), 339, July 1940

This observatory is at the bottom of a suburban garden of rather more than average size, affording fairly good sky-room. Its two main drawbacks are street lights (which have to be screened off in peace-time) and vibration from the four-track railway on the embankment of which the garden stands. A goods train stops work for about three minutes and a passenger train for half a minute. For a short time in the evening trains pass at an average of one every three minutes; fortunately two or more may pass at once, and save the observer’s time. Three telescopes and inverting binoculars are used. The telescopes are an 8½-inch reflector of 76 inches focal length, a 3½-inch refractor of 46 inches focal length, and a 2-inch refractor of 20 inches focal length. The 8½-inch is a 56-year-old Calver, hand-driven equatorial, with mirror refigured by Irving. Mirror and flat are resilvered at about 9-monthly intervals. It is massively made, and almost unshaken by any wind. The tube rotates in rings, which makes for great ease of observing but not for taking accurate circle readings. There is no slow motion in declination, but owing to good balance and bearings this is not much missed. The brass circles of 10 inches diameter are boldly engraved, but not capable of reading more closely than two or three minutes of arc with accuracy. The large mirror is pretty good, usually over-corrected, but sometimes under-corrected with a rising temperature. The flat is flat, but too small, as are most flats.

The telescope rests on a reinforced concrete platform 11 feet square, with the part directly under the telescope 3 feet thick and the rest 9 inches. It is housed in a run-off shed, bolted together in sections with the sides of weather-boarding and the roof of tongued and grooved boards battened together and covered with ruberoid. The roof is held down by hooks. Very free ventilation is provided. Four small wheels, such as are used on the bottoms of sliding garage doors, enable the shed to be run from its rails on the platform to others over a flower-bed, where there is just enough clearance to permit of lettuces being grown between the rails.

The 3½-inch refractor is by Wray. The figure and colour correction are good. Generally it is used on a simple but well-made equatorial head with small, coarsely divided circles. It has no slow motion in declination. The equatorial, when used, is fixed with two hand screws to a short iron column on a small brick pier.

Three additions were made: an 18-inch dew-cap to the main telescope, a 6-inch one to the finder, and an adjustable counterpoise to the tube made of sheet brass and filled with lead; this is fixed with a set-screw to a brass stair-rod. When a solar diagonal is used or the telescope is used on an altazimuth tripod head the balance is thus easily corrected.

The 2-inch refractor is home-made. The OG is a crown and flint ‘married up’ by Dr. Steavenson from a choice of a few dozen such found by him in a junk shop selling ex-army stuff after the last war. The result is equal to a lens costing a guinea or so. A photographic lens flange was found to fit it. The telescope body is of wood, and square. The rack mount (from a magic lantern) was found in a pawnshop; the trunnion arms are bits of brass tubing; the dew-cap is a cocoa tin without the bottom. The whole is an invaluable instrument with its short focus and wide field, and is in constant use. Its centre of balance is so near the eye end that once the telescope is on the trunnion tripod there is hardly any movement of one’s position when changing elevation.

A fixed shed a few feet away from the observing platform provides a faint light for writing notes and so on, and houses the smaller instruments and various accessories.

The regular work is observing one or two novae, all the variables on the VS Section’s list and some others, comparing new draft charts with the sky, and choosing comparison stars for the new sequences. All three telescopes and a pair of inverting binoculars are used for this work. Mars is observed with the 8½-inch and the Sun with the 2-inch, and the naked eye for keeping a record of naked-eye spots.