NOT, AS A READER once assumed in a letter, merely to tickle the vanity of their builders, have descriptions of telescopes made by readers of this department and of the two "A.T.M." books been published for years in this department, but because such descriptions offer original or interesting design features from which other builders may glean practical ideas. An advanced amateur (H.P.) recently wrote this department: "Looking back, my biggest help has been from the close study of a wide variety of clear photographs of other amateurs' work." Another amateur (S.L.) writes, "I like a plentiful supply of new ideas, wrinkles, and descriptions of all kinds, with many photographs." And W.W., whose telescope was described in this department last month, writes: "During its construction I often thought how helpful it would have been to have seen a collection photographs of instruments as built by other amateurs. I have wondered whether there might not be a place for a book containing reprints of such descriptions, from other numbers of 'Telescoptics' than I have seen, so that various ingenuities could suggest possibilities to those who were in the process of planning."

"W.W." is Warner Williams, Culver, Indiana, and at our suggestion he has now prepared a close-up photograph (Figure 1) of the driving mechanism of his telescope. "For the amateur," he writes, "this type of drive seems ideal because it does not require special cut gears to obtain a precise speed, this being taken care of through the ability of the wooden pulley J of required size, simply by turning it down to that size on a lathe." Williams' drive might most aptly be characterized as: (1) made from odd gears and elements picked up around home rather than sent away for, and (2) inexpensive.

A is the current supply.

B is the control cable leading to the hand. Switch at end.

C, motor, 3500 r.p.m., Dayton Electric Co., Chicago.

D, back gear. Reduces speed to r.p.m.

E, universal joint. Dispensible.

F, leather coupling.

G, 2-to-1 spur gears from an old magneto.

H, 2.2-to-1 spur gears. The smaller of these is behind and attached to the larger gear at G.

I, worm gear, 50-to-1. From an old airplane carburetor.

J, drive pulley (wooden) turned to the size which gives final desired speed.

K, steel driving tape sliding on this pulley serves also as a friction clutch. This is especially convenient because it requires no manipulation at any time. The tube may be turned at will, without stopping the motor, yet when re-leased by the hands it starts following at once.

L, idler pulleys to carry steel tape around the roller bearings, M. which carry the expanded polar axis. These are held in tension by means of a spiral spring attached to the respective pivoted arms which carry them.

THOUGH at first glance the telescope shown in Figure 2, made by Arthur W. Sear, 550 Windsor Ave., Stratford, Conn., appears conventional, it embodies eight interesting features to which we will call attention by italicizing their key words in Sears' description, which follows: "Optically, the telescope is a conventional 6", f/8 Newtonian. My son is shown posing at the ocular and is holding the control box in his hand. The boy is nearly six feet tall, which will give a measure of the mount.

"Detachable handles, inserted through openings and guides, are used to wheel the telescope, wheelbarrow fashion on its 10" rubber-tired wheel, from the garage to a convenient location. Removing the handles after the telescope is adjusted eliminates the danger of tripping over them in the dark. The power cord is long enough to permit setting up the telescope in any part of the lawn. The mounting is not excessively heavy and has a high degree of rigidity. The leveling screws could easily be a source of lateral wobble but this has been prevented by having the screws push down against a sturdy A-frame which is hinged along the base of the triangle, thus giving diagonal bracing.

"In order to point the telescope accurately it is essential to have the polar axis properly oriented. To permit setting it up quickly have permanently attached a small auxiliary telescope just above and parallel to the polar axis This auxiliary telescope has a special home-made reticule with a small circle 1 degree away from the center of the reticule. The offset is very nearly equal to the declination of Polaris. A long focus ocular permits insertion of a prism diagonal between reticule and eyepiece. This makes for easy use without inverting the image at the reticule. If the reticule sleeve is turned so that the markings on the sleeve indicate local sidereal time, it is only necessary to jog the mounting around and adjust the leveling screws until Polaris appears in the center of the offset circle. The accuracy of alining the telescope by this method is perhaps within 5 minutes of arc, so that the probable error is well within practical limits. Setting up the telescope requires only a couple of minutes and the method permits accurate orientation of a portable telescope.

"A type CZM Telechron motor housed in the square box drives the polar axis at sidereal time and works with negligible error through a gear combination of (51x79)/ (49x82), which is equivalent to the ratio given on page 322 of 'A.T.M A.' The polar axis drive includes a differential gear so that a small reversible motor can be switched on and off to move the telescope slowly in right ascension, for scanning slowly over an area of the sky, without interfering with the sidereal drive. The box mounted on the declination axis contains a similar reversible motor for scanning north and south. The scanning motors drive the telescope at approximately 6 degrees per minute. This speed is a little fast for the highest power eyepieces but is perhaps a good compromise when the low powers are considered. Friction clutches on both axes slip when the tube is pushed by hand from one part of the sky to another. The scanning motors are controlled by switches in a small box at the end of a 6' cable. A small electric lamp with a red lens is located in the end of the control box. This lamp is convenient when reading the scales or making notes. The red light does not seem to disturb the adaptation of the eyes to darkness.

"The floating R.A. circle sidereal drive system ('A.T.M.', page 145) simplifies the problem of finding a sky object. The right ascension circle is mounted on a sleeve that is free to turn on the polar axis. The sleeve and circle are driven through an independent worm gear at sidereal time. If the right ascension circle is once set so that is position is correct it will follow the stars as long as the power is turned on. Two pointers, 180 degrees apart, are rigidly attached to the polar axis and are adjusted so that when the telescope is pointed straight up one of the pointers will indicate local sidereal time on the R.A. circle. Or, if the telescope is turned to any part of the sky, the pointer will indicate the R.A. of that direction.

"The oculars are individually mounted in adapters which plug into the main fixture, similar to automobile lamps. Each eyepiece is focused by sliding it in its adapter where it is clamped in place. The eyepieces can be changed quickly and they are automatically in focus when they are plugged in-parfocal is, I believe, the correct word for the arrangement. A micrometer screw on the main fixture permits the user to adjust the focus for his individual eyesight.

"The polar and declination axes run in ball-bearings. The big-end bearings are 1-1/4" in diameter, the small-end bearings approximately 3/4". The housings are of cast bronze.

"I polished and figured the mirror several times and it is as nearly perfect as I can make it. With a 1/3" eyepiece the out-of-focus rings of a bright star look very much like Figure 23 on page 429 of 'A.T.M.', excepting that the diagonal covers the center. Once, on a good night, I easily split a 1.2" double and believe that I could almost reach the theoretical limit of .75" for this sized mirror, under perfect conditions.

"The tube of the telescope does not show up well in the illustration but is quite handsome. It is a 7" inside diameter plywood tube obtained from the Plymold Corporation, Lawrence, Mass. It is light, strong, easily worked with wood-cutting tools, and has a beautiful natural wood finish. The low heat conductivity of plywood is also desirable. I installed a small door in the side of the tube near the mirror so that I can place a dust cover over the mirror when it is not in use."

SILVERING is not extinct and quite a few independent-minded users of reflecting telescopes still silver their mirrors The old types of lacquers for protecting them did not meet with wide acceptance but now, in The Journal of the British Astronomical Association (Vol. 54, No. 7) F. J. Hargreaves describes experiments with a lacquering solution of Perspex, a synthetic resin plastic. This was found to be soluble in butyl acetate and excellent results were obtained with a 0.5 percent solution. The Perspex was added little by little, in finely divided form (fine filings), and stirred often to prevent agglomeration. It swells up till it occupies the whole volume of the solvent, several days being required for the solution. Attempts with amyl acetate as solvent gave too gelatinous a solution.

The mirror was set on a phonograph turntable, flooded with the solution and kept turning until dry, the ridge of fluid at the edge being kept blotted up with a dab of blotter during rotation. Perspex is British and, so far as is known, is not easily available in this country, but the methyl methacrylate resin Lucite is suggested as an equivalent. Hargreaves states that the coating he obtained with Perspex had no adverse affect on mirror performance after some months. On the other hand, your scribe learns that one large American laboratory, attempting to find a lacquer for protecting silver mirrors, ran into such difficulties with black spots on the silver coating caused by the reaction of sulfur or sulfur compounds in the film-forming material used, or else in the solvent, that the investigation was abandoned. Unless there is some other answer, this seems to leave F. J. Hargreaves of England smarter than the Yankee laboratory in question, and some reader therefore may wish to appoint himself a committee of one to dig farther into the matter and report findings. There must be some lack o equivalence somewhere.

ADVERSITY has sharpened the wits of two amateurs, one a youth of 17 with a non-functional arm (polio) who made a mirror with one arm, the other who has pushed his mirror disk back and forth interminably by means of shoulder muscles working against boards tied to his non-functional arms (polio) as stiffeners and pushers.

Several advanced amateurs recently presented the first with an RFT made jointly but still he goes ahead, one armed making a 4" mirror because he wants to have a variety of telescopes the same as others and because he wants to succeed. Mountings are more of a problem.

One hesitates between the probably rational advice of a TN friend who had experience with the handicapped and says it is not altogether bad them to work out their own salvation and the belief that dark and dusty corners the nation over must hid telescopes more or less set aside because- they have been superseded by the latest loves.

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