One of the best observatories is the simple straight-sided box type, equipped either with a slide-off roof or a traveling gantry roof as shown on the opposite page. However, there is this to be said: None of these straight-line "chicken-coop" types of structure look much like an astronomical observatory. The amateur may perhaps be pardoned if he prefers his neighbors and townspeople to know that the structure he creates houses a telescope.

To build the hemispherical type of dome requires no particular skill, though admittedly it involves considerable fussing and fitting. Designs vary widely. Usually the dome proper consists of a horizontal wooden ring and a number of upright curved ribs, covered with some kind of roofing and provided with a slot opening for the telescope. The whole dome is mounted on rollers and turns on the plate of the fixed building.

This building may be round or square, and who speak from actual experience will swear by the square type of building because its four corners give room for a small built-in desk, for built-in seats cabinets, bookshelves, and for a parking place for visitors, who sometimes get under foot in the more constricted, round type of observatory.

THE roof-top observatory of D. B Pickering, of East Orange, New Jersey, the well-known variable star observer, is a good illustration of the square type. There is no mystery about the building proper, exclusive of the dome; it is simply a square structure built on top of the house. Note that the entrance is not through a trap door in the floor but from the roof through a door. This leaves the floor clear. Pickering did not run a masonry pier to the ground, as many think imperative, but rested the telescope pedestal on cross timbers attached to the roof. Will the vibrations of the house not destroy the good seeing? Pickering's success in variable star observing says at Ieast, "not necessarily." The same bogey was faced when a large telescope was placed on the roof of a 13 story building at Columbia University, but the predicted, ruination of seeing due to vibration did not materialize (Popular Astronomy, June-July, 1928; also same, Oct., 1926). Pickering saw to it, however, that the immediate flooring of his observatory did not touch the support of his telescope; he also insulated the floor against heat from the house below.

Another square type of observatory is that of George Waldo of Fairfield, Connecticut, designed by J. Ernest G. Yalden of 120 Woodbridge Place, Leonia, New Jersey, a variable star observer. This has a pyramidal "dome" which rotates on a circular track. The side shutter lifts off, while the small level truncation at the at the top has a lid that tips back. By the way, the shutter should be at least 24 inches wide; a narrower one is a nuisance. It may, if one prefers, be made in two halves, like a sloping cellar door, opening outward.

ALBERT F. SCHROEDER, 1076 Forest Cliff Drive, Lakewood, Cleveland, Ohio, kindly let us see some drawings from which several observatories, including one in China, have been made. The original drawings can not be reproduced but the accompanying sketches based on them may serve to give ideas concerning a good structure The main elements are: A solid circular track, for which wood, if leveled well, will do; about eight good roilers (Charles D. Higgs of Fontana, Wisconsin, used roller skate wheels-see Popular Astronomy, Aug-Sept. 1928); some kind of device or guide to keep these rollers on the track (here Mr. Higgs used eight more skate rollers bearing sidewise, while the sketch shows Schroeder's method), something to keep the dome from being lifted off by the winds, (Mr. Schroeder uses simple iron hoop stock bent to embrace but not touch the dome ring, as shown on sketch). The maker may juggle and recombine or revise these or other elements to suit his own taste. Past experience with amateur ingenuity in telescope construction gives promise of a wide variety of new ideas; some of which will be good and a few better yet. The average amateur dislikes being pinned down to a standard, inflexible design to copy. He prefers to do most of his own designing.

A good dome ring can be made of 7/8-inch pine stock cut to proper radius, lapped alternately, glued and screwed together. The vertical pieces are made in the same way. This makes a heavy dome, but one that will "stay put" in all weather. Any kind of roofing will do, from unsupported canvas, giving the "starved dog" effect, to sheet metal-suit your own skill, taste, patience and pocketbook.

SOME good hints and a few plans will be found in Bell's "The Telescope," Chapter 10, and others in various back numbers of Popular Astronomy (see A.T.M., page 260). In the average case, however, an ingenious amateur will prefer to "roll his own," thus giving him the right to take credit for the whole job. We have no "blueprints, instruction pamphlets, or set specifications" , of any kind. Those who expect to hire a carpenter to do the job may need these, it is true, but if anyone plans to have it done in that manner the best thing is to go to a professional designer of observatories. The above, which is not to precise a description, was written for the fellow who enjoys doing his own jobs.

Amateur telescope making fans maybe interested in knowing that the hobby is still going strong-stronger, in fact, than at any time since 1926. This is the first year in which interest has not dwindled to a trickle during the hot months.

The Society for Amateur Scientists (SAS) is a nonprofit research and educational organization dedicated to helping people enrich their lives by following their passion to take part in scientific adventures of all kinds.