Baretic's letter reached these offices March 5 and not long afterward Jugoslavia was in the war. The Italian army was able to occupy his town of Susak, which lies just east of Fiume; there was no opposition, according to the daily press. One wonders where the telescope is now.

A telescope of this kind has no tube-simply a "spinal column" for support. Readers not familiar with telescoptics often ask whether this is all right. A tubular support for the optical elements of a reflector is mechanically convenient, also conventional, but is not necessary from an optical point of view.

PHOTOGRAPH of a grinding machine and amateur telescope maker, reproduced in Figure 2, reached us just before the first act of World War II, from Robert Wehn, Berlinerstrasse 37, Wermelskirchen, which our atlas shows to be close to Köln, or Cologne, Germany. We hinted to Herr Wehn that perhaps a Prussian telescopemaker's work would receive a better hand at some more fortunate time in world history and filed away the material. Now that things are worse, rather than better, we dig it out and publish it. Why? Just contrariness—we were born under the sign of the goat and goats are contrary; we had one.

Wehn says the machine was made by himself, according to the model of R. W. Porter. The power is a 1/5 horsepower motor and the spindle, crank-shaft, and main arm turn on ball bearings.

As Köln has been bombed many times, one also wonders where this apparatus is now!

IN his letter, Wehn recommends what he calls a "goatsfoot" for scooping out the channels in pitch laps. A goatsfoot is just a little rectangular piece of sheet metal, bent V-shaped and inserted in a wooden handle. The unchanneled lap is tipped up at an angle of about 45°, the goatsfoot is heated and started at the lower edge, cleanly cutting out and half melting out a strip of pitch as it is moved upward. This idea, in different variations, has previously been used by a number of American amateurs.

J. F. Bauer, Altoona, Pa., does it with a hot cold-chisel (if you'll pardon the term), ground to an edge having the shape of the desired channel section, held vertically and drawn along the lap as a plow. This, however, doesn't get rid of the two ridges pushed up on either side of the plow.

Wm. W. Peters, of the Department of Physics at Santa Barbara College, Santa Barbara, Calif., marks off the lines for the channels and then softens the pitch adjacent to them with a piece of electrically warmed resistance wire stretched across a hacksaw frame. He then uses the scraper shown in Figure 3 to remove the pitch.

Our vote still goes to Bill Mason's Hot Plow principle, described here in December, 1935, and now repeated.

Figure 4 tells the story, except that Mason said: "Do not try to make the groove full depth at the first stroke also pull the plow through the pitch rather than push it, and do it slowly."

Figure 5 is a modification of this design, devised by Prof. Henry L Yeagley, of the Pennsylvnia State University. Here the plow is attached diagonally to the end of the soldering iron and the lap is held vertically so that the plowed out pitch automatically falls aside.

Russell Porter tells us that the workers in the optical shop at the California Institute of Technology do it thus: The lap is poured and fixed in a horizontal position. A large knife is slowly passed through a flame, which heats it, and is then drawn through the lap. This melts and draws off some of the pitch. The pitch is scraped off by a V-shaped "scraper-offer" and, after several repetitions of this, the channel is finished.

The "Pittsport Door Mat," so-called, or rubber grid, for making laps semiautomatically, as devised in 1935 by amateur telescope makers Everest, Munn, Morse, and Carlson, is still to be had, we learn, from the original makers, The H. O. Canfield Co., rubber works, Bridgeport, Conn., postpaid anywhere for a greenback. Its use is explained in "A.T.M.A."

STELLAFANE convention, Saturday, August 2.

EVEREST, in "A.T.M.A.," suggests that abrasives used in grinding be washed, or settled, even when taken

directly from the can as purchased. Your scribe recently tried this and never a scratch was scratched. Dump the grains into a glass, stir vigorously till all are in suspension, let them settle, pour off the water, and spoon off the upper two thirds for use. If reckless, chuck the rest or, if Scottish, repeat the process with it and in turn with its remainder, and so on and on, till you faint.

Kerosene for later grinding stages, instead of water, behaves normally, and no muss need be anticipated if the oil is dispensed from some kind of container having a small, controllable flow, also if something is provided to catch all the drippings from the tool For grinding three stages, also slushing off between wets, a single pint of kerosene is enough. Fine abrasives that remain wet, or even damp, with water, will spread badly on the tool with kerosene, hence they should either be dried up bone dry first, or washed in kerosene in the first place and put on wet with it.

COMPARISET: "T.N.'s may have difficulty in judging whether the pits from any grade of abrasive have been completely removed by the next finer grade, even when using a magnifier," Cyril G. Wates, 7718 Jasper Ave., Edmonton, Alta., Canada, observes and continues:

"I have found the following stunt helpful: Suppose we are using eight grades of abrasive. Cut nine pieces of plate glass (old windshield), each about 2" square. Take one piece as the tool, and mark the back of it. With this grind both sides of the other eight pieces, each with a different grade of abrasive. Wash the tool carefully between grades, of course. Mark each sample on one side only with the grade used. Now go back to the glass on which the coarsest grade was used, and grind the unmarked side for a minute or two with the next finest grade. The object is not to remove the pits but to show a surface partly ground with grade No. 2 and containing pits from grade No. 1. Do the same thing with every other piece, and you will have a set of samples by means of which you can judge the appearance of a mirror at every stage of coarse and fine grinding."

Now and then a new—or old—reader of "A.T.M." writes this department to say that Ellison was not justified in his claim to the discovery of the auto-collimation test for objective lenses, described on page 121 of "A.T.M." Recently, while reading page 166 of English Mechanics for April 4, 1924, we there stumbled across a letter by Ellison in which he stated clearly that he only discovered it "independently." Four years later, when he prepared the material on the objective lens, for insertion in the second edition of "A.T.M.", he did not make any change in the claim for original discovery. The reader may make of this what he can.

BEFORE he made the 20" reflector described with numerous photographs in the October, 1939, number, William Buchele, 2832 Sagamore Road, Toledo, Ohio, made the Gregorian shown in Figure 6. "The drive," he points out, "is essentially the same as the Sellers alarm clock drive described in 'A.T.M.A.', page 275, except that I used a sector of a drum and a thin cable instead of a triangle plate and lever, since a lever action cannot give a uniform pull. Figure 7 shows the arrangement, also the device for plumbing up the telescope, which is a portable and is mounted on a tripod.

"The axes of the telescope mounting are bicycle hubs and they moved so easily that I had to add a

counterweight to keep the cable tight. Both axes contain small clutches and worm gear slow motions.

"The f.1. of the primary is 27 1/2'' and the e.f.1. of the two mirrors is 165-much too great for a 6"."

Recently, Buchele added to his collection the 12" Cassegrainian shown in Figure 8. He writes:

"The focal length of the primary is 29", which means a deep curve, and I had to bear down on the mirror 14 hours merely to parabolize it. [On two mirrors of even shorter focal ratio, Lower, also Ferson, parabolized mainly in grinding.-Ed.]. The secondary was even more difficult. The effective focal length of the telescope is 100".

"The finder is a 3 1/2" of 22" focal length, with objective taken from a projector. Not quite achromatic but not bad. However, I do not need the finder, since the field of the Cassegrainian itself is wide.

"I have also built the clock described by Souther in 'A.T.M.A.', and it works fine. The hour index is stationary and the face of the clock has numerals, 1 to 24, with a complete star map of principal stars down to -30°. This rotates in a counter-clockwise direction. I have it mounted on the north wall of my observatory and the illusion is very realistic, with the star map rotating just as do the stars above, at sidereal rate. The minute hand rotates in a clockwise direction, with the minutes lettered on the glass, which, of course, is stationary."

Asked how the job of building the clock went, Buchele states that "it was interesting. I did not have any real trouble. I believe the cost was lower than Souther estimates in 'A.T.M.A.'"

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.

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