The Amateur Mirror Makers of Switzerland, with groups at Schaffhausen, Geneva Berne, St. Croix, and isolated individuals elsewhere, have held national conventions. Through this column they transmit good wishes to their American fellow-addicts and/or fellow-sufferers.

It began in a small way before the war when Hans Rohr of Vordergasse 57, Schaffhausen, Switzerland, acquired a copy of Amateur Telescope Making and wrote to this department. As his interest in telescope making continued, Rohr occasionally wrote again. During the war he made mirrors and lent his townsmen the only copy of Amateur Telescope Making then in Switzerland. He prepared, after the war, to inoculate his countrymen with the telescope-making virus.

This plot he carried out successfully. Mirrors have been made in Schaffhausen in classes of 21 participants, then 16, and later 12 in a community of only 23,000. There were mechanics, electricians, a confectioner, a newspaper correspondent, a mathematician, teachers, gardeners, mill workers, physicists, bookkeepers, students, chemists-people with much the same backgrounds as the amateur astronomers of the U. S.

No account of all these activities, long and faithfully reported to this magazine by Rohr, has previously appeared because details of the telescopes built were omitted, but these have now been sent. (Europeans show relatively less interest in mechanism than Americans do, but perhaps this is a more mature point of view. We go overboard on mechanism, and on group social activities, but we forget to use the telescopes we make-as do the more serious members of the British Astronomical Association. We seriously observe variable stars, but few who do this make the telescopes with which they observe.)

The mountings of the Schaffhausen telescopes are identical. They were designed: and made by a group of engineers within; the group and then sold to those who had made their own mirrors. When a nation of individualists like the Swiss, who have the largest number of inventors per capita; of any nation, mass-produce their amateur telescopes, an explanation is required. The Swiss amateur telescope makers chose this approach to lower the cost so that more people could own telescopes.

The Schaffhausen mounting, which Rohr aptly calls the "ironing-board mounting," is based on Russell W. Porter's simple design in Amateur Telescope Making, - page 29. Porter's elementary design, however, is elaborated considerably. The base of the mounting is made entirely of wood and rests on two adjustable hand screws and a fixed support at the apex of the base triangle. When the base is lifted by means of a handle near the apex, the weight of the telescope is taken from the screws and shifted to two little wheels which at other times do not touch the ground. The telescope may then be trundled about like a wheelbarrow.

The polar and declination axes are of 1 1/2 inch gas pipe, and are provided with adjustable conical nuts which also serve as bearings. Four steel cones, two for each axis, rotate in conical holes in large cubes built up of wood glued crosswise.

Each axis has its worm wheel and worm. The worm wheel is toothed around its entire diameter, permitting full freedom of movement. In the drive between the worm wheels and the shafts are friction slip rings which permit quick change in direction without the use of the slow motion worm drives. The worm shafts are extended several inches on either end. This lends convenience. Springs on them take up end play. The "ironing board" of the tube is reinforced with a deep spine attached to it edgewise. At its lower end is a deep box with a hinged lid, which protects the mirror.

The eyepiece-adapter-prism unit, with three-point adjustment on the prism, may be moved along the axis of the ironing board by a slide, for focusing either quickly by hand or slowly by a screw. A curved metal sheet protects the prism and helps exclude extraneous light.

The finders are merely metal rings crossed by wires. These project from the end of the ironing board. Rohr says the scope has proved to be very rigid.

In the background of the photograph in Figure 1 are three identical variations the same theme. These are "twin baby carriages," each containing two six-inch mirrors and two eyepiece units, permitting two observers to study the same object simultaneously. These telescopes have proved to be too heavy and clumsy.

The Schaffhausen amateurs load their scopes on trucks and concentrate them in public places to give their townspeople evenings with the stars. As many as 1,000 have attended these gatherings.

It now turns out that the Schott firm still operates three plants in the American zone of Germany, one at Landshut, in Bavaria. The U. S. agent is still the firm whose name is given in Amateur Telescope Making-Advanced, page 226 Since June 1, however, the route to Chance Brothers has been changed. Through the good offices of Horace E. Dall of England the following statement from Dr. W. M. Hampton, Technical Director, Chance Brothers, Ltd., Smethwick, Birmingham, England, has been received. "We are anxious to supply telescope blanks to anyone in the United States wishing to buy them, and in these days of air mail we have decided that we can deal with these enquiries more advantageously directly from England."

As an example of what Chance Brother can furnish, the firm supplies blanks in BSC 1.518/64.1 or Hard Crown 1.519/60.4 and the DF would be either 1.617/36.6 1.620/36.2, or 1.623/36.0 at option. Blank are at least one-ninth of the diameter in thickness and polished on the flat faces. Three and a half inch pairs, postpaid, are 46 shillings ninepence, 4 1/2-inch pairs, 9 shillings ninepence. Dall calculates that this is roughly $9.35 and $19.35 (local U. S. post offices supply current exchange, rates). Import duty, probably at 53 per cent, will be payable at the local post office on receipt. Other glass in disks or slab is also available.

Dall states that the British glass is made of sand from an island in Scotland which is relatively free from color-causing iron impurities. Hence the glass is high in transparency. (Are the Scottish too thrifty to put a little iron in their glass sand?) Dall suggests the 1.519/60.4 al 1.620/36.2 combination, which affords three equal curves and a plane, with freedom to a high degree from both spheric and chromatic errors. He also advises f/15. The triple radii are 22.0 inches for the 3 1/2-inch and 28 1/4 inches for the 4 1/2-inch giving foci of 52 1/2 and 67 1/2 inches, respectively. If the amateur telescope maker departs slightly from these radii it is of no importance, provided all three radii are alike. The near plane surface of the flint does not have to be plane to the accuracy of a flat. Even a ten-fringe departure will have negligible effect on performance. Of far greater importance, Dall adds, is regularity of figure. He advises cementing, which reduces defects of polish, but recommends a soft cement to be unbaked and renewed after two years.

This avoids the thermal stresses set up by hardened cements that cause astigmatic star disks in many cemented and baked objectives. He urges final centering and edging to give completely symmetrical star disks in and out of focus.

BARNESITE, now widely used in the optical world as a substitute for rouge in polishing glass surfaces, is not, as some seem to believe, a synthetic material, but is a product of nature. Barnesite, with its relative, cerium oxide, is derived from monazite sands found in Brazil. Data on monazite sands will be found in textbooks of economic geology. In some granites and gneissic rocks there are small amounts of anhydrous phosphates of rare-earth elements, the chief ones being cerium, lanthanum, praseodymium and neodymium.

It would he very costly to extract these rare-earth element minerals from the solid native rocks, but in some places nature has already done the job. Just as gold from disintegrated rock may lodge in stream gravels as placer deposits, so are monazite sands from rock disintegration lodged and found in streams. Actually in Brazil and India some of them have washed from the rivers out into the ocean and are found on beaches. On the Mohs scale the hardness of monazite sands is 5 105.5.

Cerium oxide and Barnesite have been studied by the W. F. and John Barnes Company with their electron microscope at 6,000 diameters' magnification. The accompanying illustration is a remarkable electron photomicrograph of Barnesite No. 85, the commonest variety. It was taken at 4,300 diameters (which defines the resolution) and is reproduced here at about one-third size. The particle size is about 15 microns or about .0006 inch. and he little bright spots on the hexagonal crystals are actual lacy openings through them. After examining this photograph, your scribe put some Barnesite under his lowly microscope's utmost best, or 240 diameters, to find that even with this low magnification the hexagonal crystals were easily seen. The little holes in them were not resolved but were "visible" by self-hypnosis. Even less than 240 diameters suffices to show the uniformity of particle size in Barnesite, a quality valuable in optical work.

The Barnes Company has discovered a remarkable fact. If these same crystals are put in a ball mill and broken down to about one eighteenth the .0006-inch size stated, as they probably are during polishing of glass, they still polish as fast as ever. No laboratory has yet established a relation between particle size and polishing power.

An observer closely connected with the optical abrasive industry, whose work takes him to many plants where precision optical work is done, says he often sees Barnesite slapped far too freely on polishing laps. This actually slows down the polishing. The same is true of rouge. In the best shops, on the other hand, it is hard to see any of these abrasives except what is actually in the pitch surface of the laps, and little of that.

EDWIN F. BAILEY, assistant at the Fels Planetarium, Philadelphia, reports suspicious evidence (though he wishes it called no more than this) that he may have stumbled on a method of forestalling and correcting the curse of mirror making called the hyperbola. "While making several mirrors," he says, "I have found that a change from rouge to Barnesite reversed this tendency. Is this due," he continues, "to (1) Barnesite, (2) Bailey or (3) unknown factor x?" He seeks a check by others, to eliminate the second factor.

THE finishing emeries called garnet fines, more recently called UO fines, have now been used by a number of amateurs none of whom has reported other than favorably. These are manufactured by the Universal Shellac and Supply Co., Brooklyn, N. Y. They come in graded sizes designated UO 3O, UO 28, UO 25, UO 20, UO 16, UO 14, UO 12, UO 10, UO 8,UO 6, UO 4. The numerals correspond to average grain size in microns, one micron being about 1/25,000 inch. From the above sizes any desired series may be selected. After much experience with garnet fines the Ferson Optical Company finds the series UO 30, UO 14, UO 4 excellent, followed by rouge. Fred Ferson suggests that amateurs could make two of these three suffice, that is, UO 30 and UO 1O, if the last wet of Carbo were well rubbed out.

Suppliers and Organizations

The Society for Amateur Scientists
5600 Post Road, #114-341
East Greenwich, RI 02818
Phone: 1-401-823-7800

Internet: http://www.sas.org/

At Surplus Shed, you'll find optical components such as lenses, prisms, mirrors, beamsplitters, achromats, optical flats, lens and mirror blanks, and unique optical pieces. In addition, there are borescopes, boresights, microscopes, telescopes, aerial cameras, filters, electronic test equipment, and other optical and electronic stuff. All available at a fraction of the original cost.

SURPLUS SHED
407 U.S. Route 222
Blandon, PA 19510 USA
Phone/fax : 610-926-9226
Phone/fax toll free: 877-7SURPLUS (877-778-7758)
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