Mrs. Bessie M. Brownlow, 288 North Eighth St., Marshfield, Oregon, writes: "In perfecting the instrument shown in Figure 1, the Scientific American's book 'Amateur Telescope Making' was consulted freely and frequently. For the mirror a disk of commercial plate glass, 8" in diameter and 1/2" thick, was used. Grinding was done outdoors with the tool mounted on a deeply set post, and the time consumed was 8 hours, 5 minutes.

"Applying the Foucault test, after a short period of polishing with the conventional pitch lap, revealed that I had developed a hyperboloidal figure. I could, of course, have reversed my disk and gone through the process of re- grinding, but instead I chose to rub out my error with rouge, and from that point forward I worked 'up-hill'. I poured a new lap and proceeded, but shall not attempt to explain at length the altering of facets and modification of strokes which were necessary before I was able to detect the shadows which told me that at last I had achieved a satisfactory parabolic surface. Final tests were made on Saturn and Vega with the mirror temporarily mounted in the tube, and even in its unfinished state the image was sharp and well defined."

Mrs. Brownlow states that two sons assisted to the extent of devising the cell block and making the mounting, She also gives credit to Mr. H. B. Donahay, who had previously made two Newtonians, for his counsel.

WE had always heard that H. E. Bussey of Atlanta was a wizard telescope maker who followed the hobby years before there was any "A. T. M.", but now it appears that the same household holds a wizaress as well. Figure 2 is a focogram of a mirror made by Mrs. Bussey, and Figure 3 is the ronchigram. The mere man in the case writes: "My wife had listened and looked in silence at 25 years of my efforts to make a good mirror. She said, some time ago, that if the materials were provided, she would prove that a woman could beat a man at it. I didn't like the way she said it, the man of course being myself, hence materials were immediately produced.

I was not permitted to touch the mirror, except that in final figuring a 'pile of rocks' showed up in the central inch and I was permitted to use a small polisher to remove them, and of course I did this with careful supervision and copious advice from Mrs. Bussey. The mirror is excellent. A hair got across the film and looks like a scratch but there are none, and the central spot is the photographer's fault. I was the photographer "

And Mrs. Bussey writes: "I realize that it would have been utterly impossible for me to have produced anything like as good a mirror if it had not been for the guidance I received,"-a graceful recognition, though we hate to publish it, preferring to believe that the ladies can do it without any help. In fact, we know one who could but, confound it, she won't.

SOMETIMES we wonder just how important it is in the average case to test a mirror across different diameters. Once the test rack is adjusted so that the reflected cone strikes the most convenient place to do the testing, it is always a temptation to place the mirror on the rack with the same diameter up (usually determined by some landmark or blemish on the disk). This may have the unhappy result that some kind of flexure is accidentally masked, but it is human to take a chance, on the presumption that the figure itself is a surface of revolution and the flexure, if any, will sort of "unlax" if talked to in nice purring language-which it won't. From the depths of our stock drawer we fish up an old photograph, Figure 4 sent in 1928 by Mr. Henry H. Mason of Florida, since deceased. It is self-explanatory-a belt hung from a pulley, with a little crank for rotating the mirror. Before his death Mr. Mason was building a large (20"?) Cassegrainian and had a large Ritchey-type grinding machine. These remain at East Pensacola, Florida, a fact which may interest some southern amateur on the look-out for something that ought to be put into use.

AS these notes are being written, on October 15, it is at last possible to say something a little less indefinite about that "new book" we have been promising for a year or so. At last we were able to get in all the many contributions and work them up into a single pile and this, when sent to the printer on September 18, made a manuscript of 860 typewritten pages. This is now being set in type and every day or two brings us a dozen more galley proofs to be corrected and sent to the authors to be again read and corrected. As there are just 47 chapters, some of them as long as many books themselves, all this is quite a "job of work" (try it and see).

When will the book be ready? We still don't know, and if you are impatient please don't shoot the editor-he is doing his best We have set our hopes on being "out of the trenches by Christmas." Piloting a complex book through preparation is worse than rearing quintuplets, and this is a complex book-in addition to which there will be a lot of it-pretty close to the size of "A.T.M." and on the upper side at that.

Here are some of the chapter subjects: Everest on his close mirror technic. (He was asked to set down "everything he knew," and this item should run to 30 pages of compact dope, all practical and definite. If you've seen some Everest mirrors you'll know what that means.) Chapter on use of sub-diameter tools. One on metal 3 tools. Another on metal mirrors. Warner on detecting astigmatized mirrors-a subtle game, this. One on the Zernike test, by Dr. Burch, English physicist. Huh-what's that test? It's a new one and mighty interesting. Selby on flat making-full, detailed dope. Clark on small lenses and eyepiece making-all practical and very detailed. Taylor on the metal parts for a refractor, likewise practical. Kirkham on rifle sights. Haviland on the refractor-the longest chapter in the book, about 40 pages uniform with those of "A.T.M." Chapter on making setting-circles. H. A. Lower on design of clock drives, with auxiliary chapters on spring drives. A long, very detailed section on the Springfield mounting, by Porter and Ferson. Porter has revised his famous mounting and made it neater, heavier, and more rugged. He tells how to make the patterns, Ferson tells how to cast them, and Porter again tells how to machine and finish the whole mounting. Detailed dimensioned drawings-the whole Springfield down cold.

To continue: Making a 19" reflector. Schmidt, telescope. Camera obscura, by Dall-this is an interesting item. How to make a Synchronize clock, by Soother. Micrometers. Chronograph. How to aluminize mirrors, by Strong. Scanlon on observatory design. Meteor timer, by Halbach. This the main drift in Part I, but much has been skipped.

Part II, a much shorter part, more on the use than the making of things Halbach on organized observing. Millman on meteor photography. Von Arx on celestial photography and so on for nine more chapters. We hope to publish next month a more detailed announcement of all chapters in the book, and later the precise data.

What is the name of the book? A year ago it was to be called a "Supplement" to "A.T.M." Then it grew too big for that and we dubbed it "A.T.M., Vol. II." Later we became afraid the uninitiated beginner would think he had to get this as well as "A.T.M.", all at one time, and would pass out, so we renamed it "Amateur Telescope Making-Advanced," and that's final; we call it "A.T.M.A." Hence this book isn't a part of "A.T.M." but a wholly separate book-though it is being printed uniform with "A.T.M." in every way.

WHEN Prof. Russell's article on the red reflection nebula near Antares came in, and mentioned a Schmidt camera used by the Yerkes staff at McDonald Observatory in Texas, we suddenly recalled that C. H. Nicholson, one of the Amateur Telescope Makers of Chicago, made the optical elements of that camera. Urgent requests for data and a photograph brought the former from Mr. Nicholson and the latter, Figure 7, from Dr. Struve (through the kind assistance of A.H.C. of Chicago, who can produce, at instant's notice, anything anybody wants). Mr. Nicholson writes:

"Dr. Otto Struve, Director of the Yerkes Observatory of the University of Chicago, who is also in charge of the construction and operation of the new McDonald Observatory, indicated to the Chicago amateurs his inability to produce from professional makers two Schmidt cameras to be used in connection with the quartz spectrograph and the 82-inch telescope of the Texas Observatory.

"As a good deal of original research hinged upon the procuring of these in instruments, Dr. Struve suggested that the Chicago Amateur Astronomical Association attempt the task as one means of aiding in the advance of astronomical knowledge. Mr. William Callum and Dr. A. H. Carpenter, the guiding spirits of the Club, requested me to build the first camera.

"The specifications for this camera were that the mirror was to he of Pyrex, 122 mm clear aperture and 180 mm focal length, with a correcting plate of LV glass at center of curvature and of 92 mm clear aperture.

"Although the mirror gave me no real trouble, I found the correcting plate very difficult to figure, for the reason that it was necessary to do all the correcting by fine grinding with small tools and then repolishing to examine the figure. This involved a great deal of time, as it is very easy to make large errors when figuring by grinding in this manner. Testing was done by pinhole at focus of the Schmidt camera and the knife-edge at focus of a 6" telescope. All curvature was placed on the front surface, necessitating a convex curve at the center, changing to an equal concave curve at the edge of the plate.

"Upon completion it was tested by Dr. Morgan of the Yerkes Observatory Staff and found to yield star images as small as he had ever seen; their size being limited by the grain structure of the photographic plate and were therefore less than the resolving power of the optical combination."

Dr. Struve points out that the photograph (Figure 7) shows the camera "in highly foreshortened form, as seen from the top. The correcting plate is in the plane o the top surface of the box, and we are looking through this correcting plate into the camera. A part of the spherical mirror shows as a white segment upon which is projected the device for holding the plate." A.H.C. states that the mounting (that is Dr. G. W. Moffitt of Yerkes and made by Gaertner.

Schmidt enthusiasts will find, in addition to the matter in "A. T.M.A.," by Russell, Wright, and Lower, an excellent article on the Schmidt, by Prof. C. H. Smiley of Brown, in the October, 1936, Popular Astronomy.

FIGURES 5, 6, and 8 show a telescope made by J. V. McAdam, a mechanical engineer, Hastings-on-Hudson, N. Y. It is a 12-1/2" Newt-Cass combination of Springfield type. The first feature is the solid concrete bench pedestal built for solid comfort-not having to straddle a pier. We long-legged fellows have a hard time folding up our hind legs in just such places, and McAdam's solution of the jack-knife leg difficulty is fine. He writes:

"Wires for the motor drive and light in. side the mounting come up through the concrete. The P.A. has a hole clear through it for locating it on the celestial pole; a 1-1/4" tube with cross-wires fits into the eyepiece tube and there is a peek-hole in the south end of the P.A. I find this ideal for adjusting: just turn the cross-wire tube till it is in the right hour for Polaris, move the mounting till Polaris is at the cross-wires, and clamp down.

"Dec. axis is a 2-1/2" steel tube (2" internal) pressed into P.A., with a 6", 10 P. gear keyed to outer end, and the casting carrying the tube rotates on this steel tubing, carried around by a worm running on the stationary worm gear. The P.A. has an 8", 10 P. worm gear with hand wheels on either end of the worm shaft the motor clutch being operated by the left thumb.

"Figure 6 shows the cell and flotation system with part of the first prism adjustment. The prism is carried on the inner end of a 2-1/2" tube mounted on the six-leg spider extending into the barrel. For a change to the Cass the prism assembly is removed. Castings of the cell can be had at cost, in duralumin.

"The final photograph shows the combination support for the Cass secondary and Newt prism.

"Both mirrors are Pyrex. A tin can cover over both ends of the barrel puts the scope up for the night, whereupon everything is water-tight without further shelter. Once I had to chop it out of the ice but it functioned, even then."

THE question often comes up, "can anyone successfully make his first mirror on a machine, with no previous hand experience to learn the 'feel' of the work?" We have generally recommended making at least one mirror by hand but advice of that kind seldom is taken willingly by a tyro who has the machine complex. Can it be done? Another question: Does anyone silver mirrors any more, or have aluminize mirrors already made a clean sweep?

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.