Schell repeated this experiment and found Prof. Pickering s words true. The upshot was the design and construction of the off side telescope shown in Figure 1, in Figure 2, and in principle in Figure 3. At first it looks about like any ordinary Newtonian reflector (except that it looks unusually trim) but- far from it! Study the upper part of Figure 3.

"The method decided upon," he writes, "was to make a mirror of a certain diameter but give it a figure the same as if it were a section cut out of a larger mirror, and to one side of the center. The image from such a mirror would come to the same point as if the imaginary large mirror were in use, but it would be sufficiently to one side of the section actually used to permit us to view it direct, or else use a flat or even a secondary, without obstructing the path of light to the mirror."

To make this mirror, which would not be paraboloidal but eccentric or lop-sided. 'it would be possible," he states, "to grind and polish four mirrors distributed around a center and blocked up with fillers, the whole assembly figured as a paraboloid and then taken apart, but it would be doubtful if the difficulties would be justified, considering the large size of the assembly.'' For this and other reasons (one, it is suspected, being that there was a more interesting, even if harder, way) it was decided to figure the off-side mirror singly.

"At this time," Schell continues, ''explained the scheme to Mr. T. C. Beede of Youngstown, Ohio, who has had 45 years of experience in producing high-grade surfaces and who has no equal, to my knowledge, in this class of work. Mr. Beede became interested.

"As Figure 3 shows, the 10" mirror is a section of an imaginary mirror 25" in diameter and 75" in focal length-long enough to use at primary focus, yet short enough to apply a future 2:1 secondary to give 15:1 final focus-that of the usual refractor, if this were desired.

From this point on the entire job is a great credit to the ability and patience of Mr. Beede. The figuring job is not one to be recommended for beginners!" [As H. A. Longer comments, "it is easy to do on paper-but what a lot of aspirin one would need before he made one on glass! -Ed.]

Well, Beede made the off-side or lop- sided mirror, and the final result was, in Schell's words, "star images that were small planet-like disks, with ring systems surrounding them more nearly of the theoretical kind than we have ever seen in any reflector. Also increased detail in the Moon and planets-for example, colors in Jupiter's bands more pronounced-due to concentration of an estimated 90 percent of the light in the central disk."

The tube used is 13-1/2" in diameter, with a small flat 5" inside focus, the image being brought out at right angles to the tube. The mirror is tilted about 1/2".

Afterward it turned out that there was already an off-side mirror at Mt. Wilson and two at the McMath-Hulbert Observatory. Schell swears on "ATM" that he did not know any such mirror had ever been made, and, even if several had, Beede figured the peculiar mirror from scratch since he had no instructions not of his own gradual making.

So far so good, but how did he do it? For that is what the reader has no doubt been asking as he read the above. This question we put up to Schell and he came through with all he and Beede had. Here it is:

"While this is written by myself, Mr. Beede has concurred in the figuring description he and I having gone over the matter the last time I was up to see him." [Youngstown 40 miles N.W. of Beaver Falls, Beaver Falls 30 N.W. of Pittsburgh.-Ed.]

"The mirror was worked by hand, face up on a fixed pedestal, throughout grinding polishing and figuring. No machine work or mechanical controls whatever were used, although a mechanical control was tried first and discarded, as it was found unsatisfactory.

"After bringing the mirror to a true spherical surface, no further movement completely around the pedestal in the ordinary way was possible. The mirror was always placed on the pedestal support in the identical position with relation to the axis line during the figuring, and a mental picture of the condition of tile surface guided the application of the figuring tools.

"The figuring tools were pitch-coated in the usual manner. Their size was varied, but they were all sub-diameter tools, the diameters varying from 1/2 to 1/4 of mirror diameter, as needed. No advantage was found in the use of tools of shape other than round, and their edges were not trimmed to a rosette, or similar form.

"Considerable difficulty was encountered in getting a proper understanding of the surface from the appearance under test (Figure 3, bottom), and the effect of the application of the tools in correction. Mr. Beede found it a distinct advantage to use an elaboration of the knife-edge, consisting of two knife-edges facing each other in the form of a narrow perpendicular slit. By this means the cut could be made from either direction, thus reversing the shadows.

"These mirrors, when placed in this position for testing, while spherical, show marked astigmatism, with the greatest apparent bulge toward the axis, depending on the position of the knife-edge, and the figuring consists of lowering this apparent bulge and bringing the remainder of the surface into collimation. Likewise, when tested with eyepiece, while spherical, the returned pin-hole image (a slit would not be satisfactory here) shows a marked coma, and as the figuring progresses, the coma will shorten accordingly, if proper action is taking place in the figuring; otherwise the distortion of image indicates improper polishing on. This type of test and the figuring to correct the surface is not unlike correcting large refractor objectives described many ears ago by Alvan Clark where he stressed particularly the local correction necessary to round up such lenses, the local figuring being necessitated by differences in the refracting power of one portion of a piece of glass compared with another portion; and is quite apart from the zonal correction having to do with spherical aberration ordinarily associated with surface conditions or gape of a lens. While we do not have this trouble in mirrors, we have similar work in figuring an off-axis mirror.

"The figuring was found to require strokes following the varying radii, as indicated by the distances from the theoretical axis, great care being necessary literally to coax the surface down without getting too deep. Also it was found that, since the reduction involves undercutting the sphere, it was best to continue this action until the extreme outer edge area (i.e., side away from the axis) blended with the remainder of the surface. In other words, it was better not to attempt a combination action of lengthening the radius of the outer zones and shortening the inner ones.

"As previously stated, extreme care was necessary in orientation of the mirror relative to the axis-line when placing the testing stand, as this would present an altered aspect, making it difficult to determine the state of correction.

"The final criterion of correction was the quality of the pin-hole image as received at the testing position after the three reflections taking place in the set-lip.

"The above is the result of experience in working three of these mirrors. The first was finished after r running up several blind alleys and getting back out of them again. I feel that an experienced mirror worker will follow this description, but no doubt if he tries it, will use his own methods and get there just the same. So much depends on the individual, and his sense of touch and experience, in this hand work, that to lay down hard and fast rules is impossible. It is easier to do it than to tell how it is done. I think it was Ellison who once said that a man could read all the books on the subject and still might not have the ability to figure a good mirror.''

Now that Schell and Beede have presented the working hints, who will undertake lop-sided mirrors? The surface is not an ordinary figure of revolution, and the work is irregular. Perhaps prudence is the better part of valor, if one is really a tyro.

FEW amateurs attain the distinction of having the results of their work published in quite so "toney'' a purely scientific journal as The Astrophysical Journal, but Dr. Otto Struve, Director of Yerkes Observatory and one of its editors, has called to the attention of your scribe in a letter, ''the recognition which the professional astronomers have given to Mr. H. A. Lower of San Diego by printing his marvelous photographs of the Milky Way. I am extremely enthusiastic,'' he adds, "about the efforts of the two Lowers, of Mr. Arthur DeVany, and of other pioneers in the construction and use of the Schmidt camera. These men have rendered a real service to astronomy and have produced results of permanent value."

Harold Lower's textual contribution to the journal named (January number) consists of but half a page of very compact descriptive matter written in the scientist's traditional objective style, but the photographic contribution it so concisely describes consists of six full-page photographs in Orion, Cepheus, and elsewhere, taken by his father, Charles A. Lower, in red light with the Lower Schmidt. These are reproduced on fine paper. "I call to your attention,'' Dr. Strove continues, "the conspicuous little nebula shown on one plate. This nebula is shown only on the red photograph and is absent on the photographs secured with violet light. An inspection of our standard photographs of the Milky Way by Professor Ross, Professor Barnard, and others shows that the object can be barely suspected on some of the best violet exposures, but it seems to have escaped previous detection and is not listed in the NGC or IC. I am mentioning this case only because I think it should serve as an additional stimulus to our amateur astronomers."

Examination of the red-filter plate mentioned, and comparison with the no-filter plate of the same area, reveals a prominent object looking like a tuft of nebular matter on the one where there was nothing on the other. And so it looks to this department, which, however, lays no claim to knowledge of astronomy (telescope making is mechanics, not astronomy), as though the Lowers had discovered at least some kind of world, even if it is not Southern California real estate. Moreover, they have themselves been discovered by the astronomers.

In the same number of The Astrophysical Journal there is a 14 page article on the lens of the 89" mirror recently figured by C. A. R. Lundin, formerly of Alvan Clark and Sons, now of Warner and Swasey, for McDonald Observatory, its author being J. S. Plaskett, Director of the Dominion Observatory, Canada. Dr. Plaskett is an expert among astronomers in testing large mirrors, having been called in by numerous institutions to test completed mirrors before their acceptance. The article shows in full detail how such mirrors are put over the jumps; too bad that lack of space prevents a reprinting it here, at least at present. Concluding his tests Dr. Plaskett states: "The quality of the mirror proved to be unequalled by any mirror previously made or tested," a completely categorical statement made possible by the fact that the mirror s maximum departure from perfection was nowhere more than seven tenths of one millionths of an inch!

IN The Astrophysical Journal for December, 1938, G. A. Mitchell of Pasadena has a five page illustrated article on "A Simplified Spectrohelioscope, " describing the construction of a rotating-disk type of instrument. Readers of the Hale chapters on the spectrohelioscope in "ATM," will fully understand the significance. The design is such that all the mechanical work except one piece can be done with a breast drill, file, and a few taps. Mitchell is an amateur telescope maker whose vocation is the manufacture of the Mitchell Motion Picture Camera, standard camera in the Hollywood studios.

MOST normally constituted scientists enjoy reading science fiction of the H. G. Wells type, provided it is original and really clever. Hearing that Harold Lower had contributed to the January number of Astounding Science-Fiction, your scribe visited the newsstand and picked up a copy to see how good the yarn would be. Disappointment! For the "yarn" turned out to be a straight descriptive article on stellar- photography with Schmidts and other fast astronomical cameras, and at that, a pretty stiff, technical one-and not astounding.

IN The Journal of the Royal Astronomical Society of Canada, H. Boyd Brydon, of Victoria, B. C., recently published four articles on the design of small observatories giving many detailed drawings of several types. These articles in separate form as a circular are now available for two bits from the society named, at 198 College St. Toronto, Ont., Canada. Incidentally, Brydon has also published an article on ''Two Inexpensive Drives for Small Telescopes," in the January number of the same journal, this also being two bits.

THE Amateur Astronomical Association of Des Moines is the name of a new organization, of which C. O. Davis, Des Moines, Iowa (no local address furnished) is the secretary.

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.