OPTIMUM IS THE word to characterize the Richest-Field Telescope, which affords a optimum broad view of the heavens.

"I enclose a photograph (Figure 1) of a 6", short-focus telescope made for me by two friends, W. F. Gale in the chair," writes G. H. Hoskins, of Ewarra, Brewongle, New South Wales, Australia. "My interest was aroused by a chapter on 'The Richest-Field Telescope,' in your book. 'Amateur Telescope Making-Advanced.'

"The telescope is 30" long over-all, focal length is 24", mirror is 6" diameter, Ramsden eyepiece, magnification 19 diameters, field of view 2 degrees.

"It struck me, when suggesting its construction, that the design could be made more comfortable to use, hence a leather-covered pad was attached to the base, so that the telescope could sit easily on a rather bony knee-it also helps to take up vibration. The eyepiece is just at the right height when one is sitting in a chair. A door handle is attached to the tube, to allow safe carrying, but it also gives a remarkably steady hold when observing-the telescope is steadier than a binocular. Another part of the apparatus and a most useful one, is the alt-azimuth mounting shown. This is extraordinarily good.

"I have used telescopes, up to 18", but in none of them have I seen such comprehensive and beautiful views of the heavens As a comet seeker it would be hard to find its equal and, for ease of use, I know of no other unmounted telescope to approach it. All thanks to 'ATMA.'"

Thanks mainly to S. L. Walkden, father of the RFT.-Ed.

ENDLESS and largely futile has been the age-old debate between exponents of the refracting telescope and those of the reflector. After years of near ostracism by American amateur telescope makers, the refractor is now in the social swim, thanks largely to J. R. Haviland's lengthy and detailed treatise in "ATMA." An amateur whom we shall designate as X, because he prefers to be anonymous, has completed a 7-1/2'' refractor (Figure 2) and says he enjoyed the job, also likes the telescope.

X says he feared to begin the 7-1/2" objective lens as his maiden refractor job but, after a talk with J. R. Haviland, he felt encouraged to wade in. The 8" flat required in testing the objective good to a quarter wave, was successfully completed in 150 hours. Then came the actual objective. "It definitely was not difficult," states X. "The edge testing jig and spherometer described by D. Everett Taylor, in the February, 1940, Scientific American is the thing. However, I found the three-ball jig recommended in 'ATMA' by Haviland was good. Using a Starrett gage on the Taylor equipment, it was necessary only to take a little care and use patience to get the crown and flint to radius and the edges within the limit of accuracy of the gage. This eliminated the bugbear of centering.

"To avoid scratches I ground glass blanks to the same radius as each curve and used these to break in the pitch laps. Figuring was rather baffling until I tried Ellison's stunt of putting a heated flannel pad in the center of the back of the flint to indicate definitely what a hill should look like, then varying lap and stroke accordingly. To save making King's test for convexes I drew on my flat-making experiences and interpreted the fringes against the concave; for this the concave should be a true surface with a clean edge. I finished No. 1 surface one fringe off, and No. 2 about three off, but this was cemented to the concave.

"The objective required about 225 hours of actual work. It is second grade Jena and of course has some striae (a pair of guaranteed discs would have cost probably five times as much.) Strange to say, it is difficult to trace any irregularities to the striae in actual performance, though in the collimation tests they stood out like a sore thumb. Under test on the stars the glass is quite satisfactory. There is much less scattered light in the field than in my reflector. The planets and, particularly, the Moon's detail, stand up much better under high power."

John R. Haviland, author of the chapter on objective lens making, in "ATMA," states that he has tested this objective against his 10" flat, and that it tests first class and has a beautiful polish. The anonymity of X is not of his own choosing, it isn't due to shyness, and the G-men aren't after him! Your scribe will forward to him private letters from readers, if addressed in care of this department.

William R. Harlow, 328 Fisher Hall, Ox ford. Ohio, states that he made a 7-3/4" objective lens, working from Haviland's chapter in "ATMA," which he praises, the job lasting from November to May. "The biconvex crown part was easy," he says, "but I had trouble with the back surface of the flint. The unit was quite a bit over-corrected and had to be separated by about 0.1". The definition of the image then was somewhat spoiled by the light reflected back and forth between the surfaces. All in all, the lens is all right," Harlow continues, "but I will stay with smaller ones after this."

A 3" is usually about the best size objective for a maiden job, (at least one previous reflector having been made). One man fob lowed this by a 4-1/2", then a 6", obtained good results from all, and has used nothing but these refractors for the past several years.

SILVERING isn't extinct, by any means, even though aluminizing today seems superior. From C. S. Walton, 5975 W. 44th Ave., Wheatridge, Colo., we recently received word that a method of silvering described in The Philosophical Magazine (London), December, 1938, pages 953-970, had been successful in his hands and that he believed it had advantages over the more familiar method. On the basis of its origins, also of Walton's praises, we asked him to describe it, which he does as follows.

"My attention was directed to an article on silvering in The Philosophical Magazine, December, 1938, written by B. Dasannacharya and Amar Chand Seth, of the Hindu University, Benares, India, which seemed to offer improvements over the familiar Brashear method. Trial met with success, so I pass the method and my experiences along.

"Clean and prepare the mirrors according to the methods stated in 'ATM.'

"Prepare two sets of solutions based on 1 gram of silver nitrate in 2-1/2 oz. water, 1/2 gram potassium hydroxide in 1 oz. water, and 6 cc. regular sugar reducing solution for each 175 square centimeters of area, including a dish, if any. An 8" mirror, for example, having 314 sq. cm. of area, with a band around it, would be silvered by preparing two solutions, each made of 2 grams silver nitrate in 5 oz. of water, 1 gram potassium hydroxide in 2 oz. water, and 12 cc. reducing solution. The water happens to be an amount that will cover an 8" mirror properly. The two gentlemen of Benares state that the concentration is not important but that the relation of silver nitrate to area is. They found one gram to 525 sq. cm. to he the best, but with prolonged depositing time I did not get a sufficiently heavy coat and preferred one gram to 175 to 200 sq. cm. Other chemicals are, of course, always maintained in the usual ratio to the silver nitrate. Two applications on the basis described will produce a heavy coat.

"Clear the silver nitrate solutions with ammonia, as usual; add potassium hydroxide solution slowly, stirring constantly; clear again with ammonia, very carefully. The solutions clear decisively and there will be no turbidity, sediment or black suspended matter left. They therefore need no filtering.

"Forget the reserve nitrate solution and the instructions to have silver in excess. The authors state that the worker should just clear with ammonia each time, and that, in the second clearing, a slight ammonia excess (a drop or two) may be desirable since the coats will be more free from spots and action will be retarded to a convenient rate. Further, they say that temperature is of little importance. I can subscribe to the workability of all this.

"The solution on the mirror, to which reducing solution has previously been added, will turn clear brown, then opaque black, then gray, and finally, if left on 10 or 15 minutes, will clear to some extent and will not form a lot of black muck as it does when using the more familiar methods. Pouring off solutions about the time they turn gray seems to be the dividing line between a bright surface and too much white bloom. The wet coat may be washed with mild soap and water to remove bloom and sediment-with reasonable care, of course.

"While I use two applications, I do not deliberately strive for as thick a coat as results, because thin coats seem brighter and have less bloom, and after five years' experience with various coats on a 10-1/2" and 12" mirrors, plus a lot of use of the 20" Alvan Clark refractor at Chamberlain Observatory, entirely on faint variables and novae which frequently were beyond reach of even the 20", I have concluded that something is wrong with the dictum, 'a thick coat is better in every way'. However, double coats produce fewer pinholes for me, which soothes my feelings. Moderately thin coats and thick coats reach about the same minimum star magnitudes in my reflectors, and their performance is exactly proportionate to the 20" refractor in that respect.

"In sum. I consider that the improvements in silvering made in India not only save chemicals, but that the process works clean and precise as compared with the one described in the Bureau of Standards circular quoted in 'ATM'."

FOR the alt-azimuth mounting a wrinkle usually attributed to the Earl of Crawford, and described by S. L. Walkden, of London, provides a fairly good rough working substitute for the drive clock used on equatorial mountings, Figure 3 is self-explanatory Walkden writes: "The scheme can be made to work pretty well for looking southward within about four or five hours of the meridian and up to about 60 degrees North Declination. It generally works suitably enough for about an hour's observation. If the eye end of the telescope is slightly over" weighted, a cord may be substituted for the extension rod."

IN "ATMA" Everest describes the use of kerosene in place of water for mirror grinding, since the cooling caused by evaporation of water causes temperature effects well worth taking note of in advanced mirror making. W. A. Mason, 1303 Lakeview Avenue, Lorain, Ohio, says he has tried instead some carbon tetrachloride, also "Prestone'' anti-freeze, diluted about 1 to, 1, and believes these are better than kerosene-though he states that he has used' them on only one mirror, hence does not wish to make this claim dogmatically. He also diluted "Prestone" anti-freeze 1 to 1 with rouge and thought it kept the rouge mixture on the lap better than water, also retarding evaporation. Mason is the author of a chapter in "ATMA" (p. 361).

"Prestone" anti-freeze used in automobile radiators, and known to everybody, has an ethylene glycol base and suffers practically no loss by evaporation. In a 1 to 1 mixture of "Prestone" anti-freeze and water, the evaporation, at ordinary temperatures, would be approximately one half that of water alone.

You invited some friends over to spend the evening looking at the stars through your telescope. They came-whereupon everything clouded up. The friends hung around through an awkward two hours, giving you the dog-eye, as if it were your fault, and you felt like a plugged nickel. Then they went home whereupon all the stars came out.

It hasn't happened to you?

This total depravity of inanimate objects does not catch W. L. Chamberlain, 519 Liberty Street, Meriden, Connecticut napping. He keeps in reserve a dummy telescope made of cardboard tubing, equipped with indirect lighting and an "eyepiece"-a sort of peep-show-and into this he slips various mounted astronomical pictures, half-tones and drawings from here and there. And he says his friends actually think these look better than the reality!

Well, when you consider that these would be mainly exceptional pictures, corresponding to rare views of the heavens taken with large telescopes; also that most persons who have studied or read no astronomy at all are disappointed when they see the stars through a telescope, because in seeing they see only with their eyes while the amateur astronomer "sees" also with the intellect then these cut-and-dried pictures probably do look better than reality to your friends, who no doubt would be too polite to say so. Of course, one could show such pictures to the visitor even without a dummy telescope, yet there is just enough of the kid in most of us to fall in readily enough with some such guise, just as we do with scenery at a play. This saves the evening when guests look reproachful.

Chamberlain wasn't, however, the first amateur to try this stunt. Holden's biography of Sir William Herschel contains a letter from Sir William to his daughter Carolina, dated July 1782, in which is revealed how Herschel tried it on King George III and his Queen when they came to look through his telescope (George III became a good amateur astronomer later on, even though as a King we Yankees think he wasn't so hot). "When the evening appeared to be totally unpromising," Herschel wrote, "I proposed an artificial Saturn as: an object. I had beforehand prepared this: little piece, as I guessed by the appearance of the weather in the afternoon we should have no stars to look at. This being accepted with great pleasure, I had the lamps lighted up, which illuminated the picture of a Saturn cut out in pasteboard at the bottom of the garden wall. The effect was fine and so natural that the best astronomer might have been deceived. Their royal highnesses and other ladies seemed to be much pleased with the sacrifice.

CONVENTIONS of amateur astronomers will be held Friday-Sunday, July 5 -7 at Buhl Planetarium, Federal and West Ohio Sts., Pittsburgh, Pa., by the Amateur Astronomers Association of Pittsburgh, 11. Clinton Kyle, General Chairman; also Saturday, August 10, at Stellafane, near Springfield, Vt., Roy J. Lyon, Secretary. All are welcome to both gatherings.

NEWTELLIAN is the name given by John M. Pierce, 11 Harvard St., Springfield, Vt., to a reflector having a small diagonal just outside the incoming beam of rays, which he has described in one of his hobbygraphs.

ADVANCED optical design sharks will be interested in a 13 page article on "The Design of Wide aperture Photographic Objectives," by R. Kingslake, of the Eastman Kodak Co., in last January's Journal of Applied Physics (175 Fifth Ave., New York). Trends is the main thread in this.

FROM The Journal of the Royal Astronomical Society of Canada, 198 College St., Toronto, Ont., can be obtained for a quarter, a practical booklet on "The Small Observatory and its Design," by Brydon, who contributed to same journal in 1939 an article describing "Two Inexpensive Drives for Small Telescopes," one drive being especially interesting. Same cost.

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.