G.E. Patston’s observatory

Streatham, London

Journal of the British Astronomical Association, 50 (6), 216, April 1940

The observatory was designed to be as compact as possible, and has a sliding roof with the supporting arms made to fold in when not in use. To obtain the maximum sky room, the ridge and part of the north slope are hinged to fold back, and a portion of the west side opens out.

The observatory houses two telescopes. The main instrument, made by the writer, is of 12 inches aperture and 80 inches focal length. The smaller one is a 3-inch Wray on loan from the Association, for use on parts of the sky inaccessible to the larger telescope.

In the mounting of the former, to avoid the expense of heavy castings and machining for the bearings, the writer made use of two cogs from an old mangle. The cog used for the thrust bearing of the polar axis had one set of teeth machined off and self-aligning ball bearings machine pressed on to it, and these are housed in rebated boarding bolted to the concrete base. The upper bearing is taken by two channel irons bolted to the pillar and appropriately slotted for altitude and azimuth adjustments. The bearing itself turns in a V groove in the inner channel iron. The polar axis is built out of 6 x 3-inch timber. The declination axis consists of two lengths of gas pipe riveted in flanges and machined to run in plummer blocks, the bore of the latter being reduced to allow for clamping. A prism is used for the secondary mirror.

Tube currents are effectively counteracted by a large tube, 16 inches square, permanently open for about half its length. The closed portion affords sufficient protection for the mirror against dewing. Included in the illustrations is a picture of the telescope taken before the observatory was built.

The telescope is driven by a small fractional h.p. motor, reduction being carried out by Meccano gears on independent shafts. The speed is controlled by a gramophone governor on the first shaft. The final transmission, by worm and gear wheel, is a friction drive designed to permit moving the telescope in R.A. without interfering with the continuous drive which is taken up at once. To achieve this a back-plate was bolted to the web of the gear wheel and bored to receive the spindle of the top bearing. A steel collar was fixed to the spindle with a taper pin, and the gear wheel rests on this collar with a similar collar above it, the wheel’s upper surface being flush with the top of the spindle which was tapped for a clamping bolt and spring washer. To prevent the upper collar undoing this bolt, through motion of the telescope, two pins were inserted longitudinally through the collar into the spindle. The whole can be clamped solid when required, and the variable clamp counteracts to a large extent the freedom of movement associated with ball bearings.

Visual observation of forty long-period and irregular variables forms the major portion of the work done at the observatory. The writer is assisting in the production of the Section’s new charts, and the 12-inch is also employed in the choice of sequence of fainter comparison stars in these fields.