Hence for small observatories other forms of revolving roof are desirable, and quite the easiest and cheapest contrivance is that embodied in the “Romsey” type of observatory, devised half a century ago by that accomplished amateur the Rev. E. L. Berthon, vicar of Romsey. The feature of his construction is an unsymmetrical peak in the revolving roof which permits the ordinary shutter to be replaced by a hinged shutter like the skylight in a roof, exposing the sky beyond the zenith when open, and closing down over a coaming to form a water tight joint.
Berthon’s original description of his observatory, which accommodated a 9¼ inch reflector, may be found in Vol. 14 of the English Mechanic and World of Science whence Fig. 179 is taken. In this plate Fig. 1 shows the complete elevation and Fig. 2 the ground plan, each to a scale of a eighth of an inch to the foot. In the plan, A,A, are the main joists, P the pier for the telescope, T that for the transit, and C the clock. Figs. 3, 4, and 5 are of details. In the last named A is a rafter, b the base ring, c the plate, d one of the sash rollers carrying the roof, and e a lateral guide roller holding the roof in place.
The structure can readily be built without the transit shelter, and in fact now-a-days most observers find it easier to pick up their time by wireless. The main bearing ring is cut out of ordinary 7/8 inch board, in ten or a dozen, or more, sections according to convenience, done in duplicate, joints lapping, and put very firmly together with screws set up hard. Sometimes 3 layers are thus used.
The roof in the original “Romsey” observatory was of painted canvas, but rubberoid or galvanized iron lined with roofing paper answers well. The shutter can be made single or double in width, and counterbalanced if necessary. The framing may be of posts set in the ground as here shown, or with sills resting on a foundation, and the walls of any construction—matched boards of any kind, cement on wire lath, hollow tile, or concrete blocks.
Chambers’ Handbook of Astronomy Vol. II contains quite complete details of the “Romsey” type of observatory and is easier to get at than the original description.
A very neat adaptation of the plan is shown in Fig. 180, of which a description may be found in Popular Astronomy 28, 183. This observatory was about 9 feet in diameter, to house a 4 inch telescope, and was provided with a rough concrete foundation on which was built a circular wall 6 feet high of hollow glazed tile, well levelled on top. To this was secured a ring plate built up in two layers, carrying two circles of wooden strips with a couple of inches space between them for a runway. In this ran 6 two-inch truck castors secured to a similar ring plate on which was built up the frame of the “dome” arranged as shown. Altogether a very neat and workmanlike affair, in this case built largely by the owner but permitting construction at very small expense almost anywhere. Another interesting modification of the same general plan in the same volume just cited is shown in Fig. 181. This is also for a 4 inch refractor and the dome proper is but 8 feet 4 inches in diameter. Like the preceding structure the foundation is of concrete but the walls are framed in spruce and sheathed in matched boards with a “beaver-board” lining.
Fig. 180.—A More Substantial “Romsey” Type.
The ring plate is three-ply, 12 sections to the layer, and its mate on which the dome is assembled is similarly formed, though left with the figure of a dodecagon to match the dome. The weight is carried on four rubber tired truck rollers, and there are lateral guide rollers on the plan of those in Fig. 179.