The wrinkle consists of a thumbscrew working in a half nut, and the virtue of it is that, while the springiness of the arm and a piece of spring brass to which the nut is attached holds it to whatever part of the screw it is placed against, it can be lifted off and shifted at once without a second's fuss. Barkelew has this wrinkle on both his R. A. and declination motions, and he writes that "if anyone is foolish enough to want to make one, I can tell him how this one can be improved without making it too fussy." His address is Great Republic Life Building, Los Angeles. This looks like a wrinkle well worth copying-study it over. Barkelew is the man who is interested in automatic photo-electric telescope guiding and who described his ideas on that subject in the August number.

ON the opposite page at the bottom you will see a picture of a grinding machine made by Clark B. Hicks of the Amateur Telescope Makers of Indianapolis, of which V. E. Maier, 1306 Parker Avenue, that city, is secretary. Maier writes that Hicks' machine works just as smoothly as the best steel ones, although it is made entirely of wood with babbitt bearings. All the rotating parts are below the top of the table. The originality of this piece of work is manifest in the photograph: the lever at the right-hand corner, for adjusting the length of the stroke while running, the "model T" drag link with ball and socket joints at either end, making the mirror "full floating," and the improved Lee ratchet eliminating all bevel gears and driving rods on the link. By adjusting the transverse arm the equivalent of an elliptical stroke can be produced.

WE learn that the Corning Glass works has supplied a 24 inch disk of Pyrex to the College of Puget Sound, Tacoma, and that the Amateur Telescope Makers of Tacoma will grind, polish and figure this mirror. Alan R. Kirkham will have charger of this job, with George Croston assisting. More amateurs doing professional work!

HERE is A. W. Everest's latest revision of the previous revisions of the revised methods of using HCF laps, complementing or supplanting Part VIII of "Amateur Telescope Making." Everest writes:

"We use HCF on the tool for bringing to a complete polish, paying no attention to the figure until then. Embed the HCF in a very thin layer of soft pitch-pitch in which at room temperature one pound pressure with the thumb nail will make a quarter inch dent in one second instead of the five seconds usually allowed for a pitch tool. The pitch layer should be thin enough so that the HCF will sink right through to the glass and become unyielding. It will maintain contact by wearing. After forming, dash on some water and rub all over lightly with a cake of Ivory soap. Then work the mirror back and forth a few times to produce a fine, bubbly suds before applying the rouge and water mixture; otherwise the rouge won't stay in place.

"The polishing action of the HCF too must be kept in mind if you are to maintain top speed. Practically no rouge granules become embedded in the surfaces of the facets, as in the classical pitch tool. It is the wedge of rouge granules that form at the edge of each facet during each individual stroke that does the work. On the reverse stroke this wedge breaks away and another forms on the opposite side of each depression-and so on, back and forth. From the above you can see that only a small amount of the rouge in the mixture can be effective. Surplus rouge is worse than useless, as it piles up to the extent that it rolls over the facets, wearing them down too fast. A heaping teaspoon in half a glass of water is sufficient. If you can look through the mirror and see all the facets as you work, all is well.

"For the final figuring I recommend a pitch tool."

Norman Shillinger, 403 Commerce Street. Wilmerding, Pa., finds that cutting channels in a lap under water will prevent chipping the lap-like cutting glass with shears under water.

HERE is a letter received from Clayton R. Tinsley, president of the Tinsley Laboratories in Berkeley, California (3017 Wheeler Street):

"Tinsley Laboratories desires to offer the following contribution: We note that not more than five percent of mirrors sent to us for silvering are fully polished. The following test, used by us on our own work, might be a revelation to many.

"Take a small reading glass or other simple lens and, using it as a burning glass, throw a bright spot upon the supposed polished surface. Either an electric light or the sun may be used, though the latter is much the better. A surface which seems quite fair using a magnifying glass in the usual manner will now appear as a gravel bed even to the naked eye. If the test seems too drastic, try it out on a professionally polished surface, such as a B. and L. prism. If the prism surface is clean and free from grease, even the most intense 'burning glass' spot can scarcely be detected by front face reflection."

At the risk of being lynched, your scribe will add that he is suspicious that many of the short, two-and three-hour polishing jobs he constantly hears of will not pass this test. Please accompany future claims with affidavits sworn on A.T.M.

The old chestnut about local figuring with the ball of the thumb is up again for discussion. We wrote to J. W. Fecker for his opinion. His reply was: "This is definitely one of those myths the origin of which nobody knows, but it nevertheless persists." In spite of this we frequently hear that this was the lost, secret method used by the great professionals. We are from Mo.

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.