HERE, for one ingredient, are some 11 originally good focograms which show what kind of work amateur telescope makers can do. The first is by Harold A. Lower, 1032 Pennsylvania Street, San Diego, California, whose 12-inch Cassegrainian telescope was described last month in this department. The focogram shown in "Amateur Telescope Making," page 225, is correct as regards the distribution of lights and shadows, but the shadows are too deep. Likewise the present one does decidedly poor justice to the original. Any such reproduction in a magazine or book is just four removes from the original: from the negative to the print, from the print to the engraving on copper, from the engraving to the electrotype, and from the electrotype to the printed page; the end-product is certain to differ somewhat from the original. While it tells much, the worker must measure zones and not attempt to judge the curve of his mirror by mere visual comparisons of shadows, except for their distribution. Failure to take such urging seriously has apparently resulted in a large crop of badly overcorrected mirrors-some that have been tested having a whole inch or more of zonal aberration. As Mr. Lower's mirror, a 12-inch, has a focal ratio of f6, the shadows were deeper to begin with than they would be on an f8. When the curve is correct the shadows will be extremely thin and tenuous; in fact a person not familiar with the knife-edge test would probably fail to find them at all. Mr. Lower gave his mirror 95 percent of the full paraboloidal correction, so be writes.

We begged him to send us a few extra prints and copies were sent by us to Professor Ritchey and to Reverend Ellison. Professor Ritchey, who, by the way, tells us he is extremely interested in the amateur telescope makers' movement-he enthused over it, in fact-referred to Lower's focograph as "the most beautiful I have seen," and added, "Please give my compliments to Mr. Lower when you write him." The Reverend Mr. Ellison wrote, "Very many thanks for sending me the very beautiful and interesting focogram of Mr. Lower's 12-inch mirror. It is perfect and typical, and had it reached me a few days sooner I should have had it reproduced and included in the illustrations in the new edition of 'The Amateur's Telescope' now in the press." (By the way, when Ellison's new British edition is ready we shall let our readers know, as many will want to purchase it.)

ANOTHER focogram-in fact a series- reaches us from Mr. E. Lloyd McCarthy, 10 Powers Street, Canton, New York. "They show," he writes, "the Foucault shadows seen on my six-inch mirror at four stages of figuring. The second represents the effect of two-inch polishers on the first, but I decided to leave these sub-diameter tools to the skill of Professor Ritchey, as this focogram clearly indicates was advisable! A little difficulty in the matter of contact produced the figure in the third. When I was finally through wrestling with this job I had shortened the focal length two inches." We reproduce this series as a back stiffener for those who are sick and weary, and the moral is, cheer up. The focograms show what can be worked out of a horrible mess if one will persist. In fact, if a mirror does not go through a lot of these preliminary monkeyshines it is almost subnormal, like a boy who is just too good for any use.

Speaking of Professor Ritchey: We journeyed over to Philadelphia a few weeks ago and saw him and the heavier parts of the mounting for his new 40-inch Ritchey-Chrétien telescope, and an article about this telescope was rashly promised for the present number. It turns out, however, that we have left ourself too little time to write it. Next month or die. This article will not, however, be aimed at the amateur telescope making fraction of our readers, but at all of the readers, hence it doubtless will seem somewhat "written down" to those who already understand telescopes.

THE Amateur Telescope Makers of Springfield, Vermont, have chosen to hold their annual convention of telescope enthusiasts this year on Saturday, August 27. This of course is only four days before the total eclipse, some 150 miles farther east in Maine. On account of the eclipse in Maine, the Pittsburgh amateurs will not hold a convention this summer but will attend the one at Springfield and take in the eclipse later in full force. The amateurs at Springfield hold winter meetings at Stellafane on the mountain top, and the snow is so deep that they must climb Mount Porter on snowshoes and skis. "After a good hot supper, the last one having been an oyster supper," says A. D. Baker, their secretary, "with the fireplace filled with rock maple logs, the flames curling upward and sending out an abundance of heat, we gather for our meeting and discuss those things in which telescope makers are interested. And then, as midnight approaches, we wend our way homeward with a feeling of an evening well spent."

Stellafane is fine in summer but still finer in its mantle of winter snows. And then, too, there are no mosquitoes and no venomous snakes at that time of the year. At last summer's convention an exasperated snake chased a lady twice around Stellafane.

Several have inquired for a list of the organized associations of amateur telescope makers. Here is the list. The Cincinnati group was organized latest-some time last winter. There are also informal groups in Little Rock and Indianapolis. Which community will be the next to organize?

"The Amateur Telescope Makers of Springfield," A. D. Baker, Secretary, Springfield, Vermont. ~

"The Amateur Telescope Makers and Astronomers of Los Angeles," E. R. McCartney, Secretary, 2940 Mount Curve Avenue, Altadena, California.

"The Amateur Telescope Makers of Chicago," William Callum, Secretary, 1319 West 78 Street, Chicago, Illinois.

The Astronomical Section of the Academy of Science and Art of Pittsburgh, Leo J. Scanlon, Sec.-Treasurer, 1405 East Street North Side, Pittsburgh, Pennsylvania.

"The Telescope Makers' Section of the Eastbay Astronomical Association," Franklin B. Wright, Chairman, 155 Bret Harte Road, Berkeley, California.

"The Amateur Telescope Makers and Astronomers of Tacoma," George Croston, Secretary, LaGrande, Washington.

"The Amateur Telescope Makers of Cincinnati," W. Clemmer Mitchell, Sec.-Treasurer, 2390 Wheeler Street, Cincinnati, Ohio.

THOSE ever enterprising enthusiasts, the Astronomical Section of the Academy of Science and Art in Pittsburgh, have just done a good turn for amateurdom. They thought so well of the Hindle monograph on the Cassegrainian and Gregorian that they volunteered to mimeograph for us 125 copies, if we would prepare the illustrations and send the monograph out to advanced amateurs who request it. This advanced monograph would be valueless to a beginner, who should first study the elementary instruction book "Amateur Telescope Making." To others seriously interested it goes for the asking and need not be returned.

Vitreosil is a material made by the Thermal Syndicate, Ltd., 58 Schenectady Avenue, Brooklyn, New York, and we know of no present reason why it should not b regarded as available for mirrors. A six-inch blank appears to cost about 45 dollars. These disks consist of an outer transparent layer of fused quartz on each side with intermediate layers of translucent fused silicon.

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.