Well, anyway, there's a lot of activity in Pittsburgh and in Pittsfield too. The Pittsfield group is made up entirely of employees of the General Electric Company.

Now comes Buffalo with a new group, the Amateur Telescope Makers of Buffalo, with 15 charter members. Thaddeus Czerniejewski, 113 Franklin Street, Lackawanna, New York, is its chairman.

Winston Juengst of Todd Union, University of Rochester, Rochester, New York, mentions the organization of an Astronomy Club in that city, which is doing meteor research and making telescopes as well.

So many have inquired about the new method of plating mirrors by evaporation in a vacuum that we have fished out the Astrophysical Journal for last June, which contained a five page article on the technique, by Robley C. Williams and George E. Sabine of the Department of Physics at Cornell University (Ithaca, New York). The work requires a steel bed-plate, a glass bell jar and a high vacuum pumping system. The bed-plate used was 22 inches square, but this depends upon the diameter of the mirror. Glass plugs containing tungsten leads must be sealed into holes in the plate. The metal to be evaporated and deposited is heated electrically by a filament and the mirror is placed about three inches distant from it. The bell jar placed over the whole apparatus must have a very tight joint at the bottom where it meets the bed-plate. A vacuum of one thousandth of a millimeter of mercury is required, and this demands a better vacuum pump than most amateurs have available.

Coating a 16-inch mirror requires 15 minutes. Chromium or aluminum may be applied. The latter has excellent reflectivities-90 percent in the yellow and 80 percent in the violet. Similar work has been done with magnesium, by Hiram W. Edwards of the University of California (Berkeley). Two years ago, Professor John Strong of the California Institute of Technology (Pasadena) sent us a description of his method, and tried to work up a simplification for the amateur telescope maker, but he later stated that the high vacuum would offer too great an obstacle for the amateur unless he had access to better than average laboratory equipment. It is believed that several amateurs so situated have experimented with this method, but the outline above is given mainly in order to show that it is probably out of the reach of the average worker. It is too complicated and too expensive.

A STUNT for silvering, sent in by Lincoln K. Davis of Campello Station, Brockton, Mass., is as follows: "Get a paper pie plate, preferably the kind made of heavy, coarse pulp, with a bottom diameter about the same as that of the mirror to be silvered. Place the mirror inside, and mark around it with a sharp pencil. Then cut out the bottom on this line, or slightly inside, and the result will be a collar which can be fitted around the mirror near the top. A soaking with shellac, pitch, or paraffin makes it tight and acid-proof. A heavy rubber band immediately beneath it helps to locate it and makes the mirror easier to handle."

Frequent inquiries received indicate a desire on the part of many beginners to build up mirror disks from lamina of thin glass. There is a big gamble in this. Doliver S. White, 232 South Alain Street, Mansfield, Massachusetts, with Leon G. S. Wood, made an 8-inch disk from four pieces of quarter-inch plate cemented with Rutland water glass. The mirror performed nicely but, in Mr. White's language, "after using the telescope for some days we discovered that the mirror was losing its figure. Immediately we tested it and discovered that the curve had radically changed. The curve was so distorted that we fine ground it and figured it again. Again the mirror gave what to us seemed a perfect performance, repeating its former performance. We have found, however, that the mirror cannot be depended upon to keep its figure more than a few days at the most. In consideration of our experiences we would not advise the use of this type of mirror.

"If any of the readers of the SCIENTIFIC AMERICAN would like a more detailed account of how we built a mirror that worked at no expense except for the chemicals used for the silvering process, we shall be very glad to hear from them."

Mr. White did not reveal the nature of the latter mirror in his letter.

We often hear of short cuts in polishing -mirrors polished in one or two hours, and so on. Here is what J. W. Fecker, the professional, has to say about this: "The amateurs and all the rest who have not already done so must depart from the belief that there is a quick way to obtain an optical surface. An optical surface is nothing less than a work of art and there is no short cut to results." No doubt some will regard this as a challenge, but . . .

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.