Some builders of telescopes-or of anything-have an innate sense of cleanness in design, and turn out jobs that are as "smooth" as a flapper-well, anyway, some flappers-without gadgets, hickerpickers, excrescences, and what-have-you, stuck on here and there. Their jobs look "finished." One such is the telescope made by Lincoln K. Davis of Campello Station, Brockton, Massachusetts. Look closely at the photographs.

"THE mirror is of 50-inch focal length, fully parabolized," Mr. Davis writes. "The mount is built around pipe fittings, faced off on the ends, to which are bolted flat iron disks which serve as bearings. The disks are held together by 1-3/4 inch iron sleeves with ring nuts to adjust the degree of friction, and between them are held six-inch, 192-tooth, steel spur gears, lapped to work with hardened worms, to provide slow motion. Between each gear and the disk carrying its corresponding worm are 133 ball bearings running in a groove cut in the disk, to reduce the frictional stress on the worm. The entire mount is very stiff and rigid, but the motions work very easily.

"The pedestal is of five inch pipe, bolted to an old machine base from the junk yard, which is buried in the ground. The mount is fastened to this by three cap screws with interrupted or breech threads, and may be removed in one minute. Dowels are provided to locate the mount accurately in azimuth each time it is replaced.

"The tube is also detachably fitted to the mount, and the whole outfit can be taken down and carried inside. The end of the tube rotates, so the eyepiece is always accessible. Circles are provided, and that on the polar axis is movable, with two indices, eliminating calculations. I did the graduating on my small screw cutting lathe, by making a worm to mesh with the large back gear on the spindle and arranging a shaft to carry the worm on one end, and one of the change gears on the other. The indexing was done by counting teeth on the change gear and calculating the resulting motion of the work carried by the spindle. The engraving was done by a sharp tool held in the tool post.

"There is also an electric drive, adapted from a synchronous phonograph motor, which is attached to the bottom flange of the mount, and goes down inside the pedestal. The gears were obtained from the Boston Gear Works from stock, and give sidereal time within .8 second per day. The motor has a 22-l/2:l gearing built in (giving 80 r.p.m. of the turntable shaft on 60 cycles A.C., so the rotor turns at 1800 r.p.m.). The gears are as follows, including the worm and gear on the polar axis:

"Nos. 2, 3, and 4 are 48-pitch brass spur gears; No. 5 is a pair of 48-pitch brass bevels; No. 6 is a 48-pitch bronze gear and steel worm to fit; No. 7 is the gearing on the polar axis, described above. These gears give a reduction of 2,584.878:1, compared with a true ratio of 2,584,902 :1. The discrepancy is about one part in 108,000, or .8 second per day. I found the slide rule a great help in selecting ratios, to be checked by dividing out.

"While my instrument is fitted with a finder, I am inclined to agree with Mr. John C. Lee who favors simple sights, so I have added them, and find them even more convenient than the finder in picking up visible objects. If the rear sight has a relatively small hole, it increases the depth of focus of the eye, so that the forward sight is sharper when looking at a distant object or star."

ANOTHER trim, neat job is that done) by Francis H. Reynolds who is an assistant professor at Clarkson College of Technology, Potsdam, New York. He says: "My first mounting was more sensitive to slight tremors than the most sensitive seismograph. When the Japanese were bombing Shanghai I had to quit observing." To replace this shimmying "seismoscope" he decided to turn out a real job, and the photographs show what this looked like when finished. It has a five-inch cast-iron pedestal which surely will not shimmy. The polar axis shaft is turned down from a chunk of 2-1/8inch cold rolled steel shafting, and that won't shimmy either. "The main brain-storm," according to the owner, "is the design of the rat trap on the nether end of the declination axis." This supports an adjustable declination axis counterweight for eliminating flexure from that axis. "1 purloined the idea," says Reynolds, "from Zeiss."

"The baptismal font you see at the base of the pier," continues this builder, "is the drive, consisting of a G.E. phonograph motor." He goes on to describe in detail the various parts-too much detail to reproduce here. This 'scope evidently is a "swell" job, adjustable everywhere and embodies real machine design.

PAUL RICELLI, Pasaje Praga 31, Jacomino, Habana, Cuba, has this to say concerning the instrument mounted on a tripod, which is shown in one of the illustrations:

Mirror: 6" diameter, 54" focus, parabolized.

Cell: Of cast bronze with screwed ring. Wall of cell and the bottom of mirror are lined with cork. An inside tripod with three coil springs pushes mirror against front ring. A second tripod with central sockets and ball attachment adjusts mirror in all positions.

Tube: 56 inches long, seamless aluminum, granulated finish, Duco, gray, sprayed, with polished German silver bands.

Equatorial mounting: On ball bearings. All in cast bronze.

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