THIS, NOW THAT it can be told, is the second half of the story of the recent Roof Prism Program of Scientific American's advanced amateur telescope makers.

In the first account, published in the May 1943 number, it was told how Russell Porter, Alex MacTavish, and your scribe, had discovered in 1941 that the nation's need for roof prisms for military instruments was desperate. Roof prisms (Amici type) were suddenly needed by scores of thousands but there had been no peacetime demand and only two or three precision opticians had learned how to make them. They were about the toughest thing to make in optics; two of their faces had to be within two seconds (1/1800 degree) of a perfect right angle, or 60 times as close as the Porro prisms in binoculars and far closer than all but the most uncommon right-angled prisms.

It was told how this magazine arranged with Frankford Arsenal to be the link between that institution and the amateurs, and how it organized 100 of the more able amateurs and throughout a year and a half coordinated their work while they progressed from single trial prisms to small and then large orders, working at home. Into this program Russell Porter threw the weight of his prestige, inspiration and all the help he was able to give. The third leader, MacTavish, had foreseen the nation's need for the difficult roof prism and, working alone and without written instructions (none then existed) had ferreted out the technique. He had patriotically turned over to the 100 amateurs, through mimeos issued by Scientific American all that he had learned, enabling them to start level with him. Who was MacTavish?

"MacTavish" was the alias for Fred B. Ferson, Biloxi, Mississippi, which had to be assigned when the Office of Censorship, after going over the manuscript of the account of May 1943, said: Give all the roof prism producers fictitious names and, for fear of sabotage, omit their locations. "MacTavish's" (Ferson's) photograph has been in "Amateur Telescope Making - Advanced," page 337, for years.

Thus the man who, out of patriotic motives, gave hundreds of tired hours to others and answered hundreds of letters while busy making his own roof prisms, was simply one of the nationwide fraternity of glass pushers-an average three-mirror amateur when he began making prisms. It is ironical that wartime necessity forbade revealing the identity of the amateur who gave the most to the Roof Prism Program.

Here is a summary of the roof prism production of the amateurs-the prisms acctually accepted and purchased by Frankford Arsenal and three large wartime military instrument makers. Most of the names look more professional than amateur. This is because assuming formal company names proved easier than to convince a puzzled world that amateurs could make roof prisms.

No conclusions should be drawn because of the large variation in production of the individual amateurs. Some unwittingly began almost too late; others lacked time or strength for the exacting work, which experience proved to be too strenuous for performance in spare hours.

F. L. Frazine, jeweler, St. Petersburg, Fla., 18 prisms.

F. A. Jasset, podiatrist, with F. Richards, Newton, Mass., 24 prisms.

G. E. Gordon, photographer, Natick Mass., 25 prisms.

F. R. Varela, engineer, Tenafly, N. J., 50 prisms.

A. H. Johns, decorator, Larchmont N. Y., 165 prisms.

G. Dallas Hanna, zoologist, paleontologist, California Academy of Sciences, San Francisco, with others of the Academy museum staff, made 165 prisms but shifted to emergency repair of Navy optical instruments.

K. E. Dykoski, assistant in astronomy, University of Minnesota, 300 prisms.

The Precision Military Optical Co., H. H. Selby, Encanto, Calif., 700 prisms. Selby later turned to essential war work in his vocation, chemistry.

The Wellsville Optical Co., Wellsville, N. Y., David Broadhead (the "Jim Fogarty" of the May 1943 account) assisted by two part-time employees and by Mrs. Broadhead in the capacity of prism inspector, cleaner, and packer, food provider, and sympathetic listener to beefs and griefs individual and collective, 1850 prisms. Broadhead's vocation, doctor and bonesetter to the motion picture projectors of S. W. New York State, afforded him considerable spare time.

The Emerson Optical Co., Inwood N. Y., Ralph Franklin, engineer, and Frank Cameron, assisted by Mrs. Cameron and one employee, were the only ones who made a large number of prisms (1700) in spare time, after doing full days' work in their vocations. For this they paid the penalty of creeping fatigue.

The Optical Associates, of Detroit, L. H. Sampson ant several other amateurs, made 4500 prisms-which, however, was only a part of their general optical work. They plan to remain permanently in optics.

The Modern Optical Co., Toledo 7300 prisms, consisted of Wm. Buchele, an amateur who had made a 20" reflector described in this department October 1939, assisted by his father, son, wife, and brothers, whom he trained to do some of the processes He remains permanently in optical work.

Ferson-Linde Optical Co., Biloxi, Miss., 11,160 prisms, was Fred Ferson of Biloxi and Paul Linde ("Pavel Uvaroff'') of Crossville, Tenn., assisted by one full-time helper trained to do grinding. Ferson remains in optics as head of the Ferson Optical Co., Biloxi, while Linde, in Crossville, Tenn., is doing individual optical jobs on the side, as he had been doing before the war. Like the rest, these two pitched the time-clock into the well and worked from 8 A.M. till 9 P.M. till they were fagged-and then kept going.

The total production mentioned above is 28,420 Amici roof prisms accepted and purchased at prices which ranged somewhat above and below ten dollars each.

What percentage of the total roof prisms produced in the nation the 28,420 represents cannot yet be stated and is not large-probably under a tenth part. Where the amateurs made up for this, and more than made up, was in quality. Their percentage of prisms accepted by Government inspectors was higher than for all or nearly all the professional producers. This is not, however, a reflection on the professional. The amateur was running a small shop and doing his own work, or the finer parts of it, himself. He had high incentive-interest in optics as a science-and, above all, personal pride derived from his telescope making days. The professional seldom could employ men having the same incentive. In other words, had the amateurs greatly expanded they, too, would have had to employ wage earners for the finer parts of the work and then their level would have had to fall to the common level, which ran from 80 to 90 percent acceptance of prisms submitted; in a few instances higher. Not all the amateurs even equalled this level but most of them considerably exceeded it. Buchele, Broadhead, and others ranged around 98 percent. On their 11,160 prisms Ferson-Linde bettered 99-1/2 percent acceptance by purchasers.

As Ferson pointed out in these columns in May, 1943, the telescope maker is judge and jury of his own work but when optics are sold to others a disinterested, tough, and hard-boiled, impersonal inspector steps in. Suppose, for illustration, the same rigorous standard were applied to the mirrors you make. For one single pit a mirror would be rejected, or for one tiny scratch visible only under a ten-power glass perhaps after you had been shown just where to look. How many mirrors would get by? That is what the prism makers encountered-greatly stepped up requirements (not a bad thing, however, since compromise would only beget more compromise, then laxity).

The amateur had much more skill compared with the field-a major part of which consisted either of new firms without optical background or old non-optical firms thrown into optical work because it had to be done by somebody-than was sensed at the time. Had this been sufficiently realized nothing would have been allowed to obstruct a plan which Porter, Ferson, and your scribe at first projected: the gathering of the amateurs in one place and in one organization-Amateurs Incorporated. To this, two obstructions arose. One was the simple fact that, until the amateurs' own ability to do this optical work of the toughest kind equally well with professionals had been demonstrated-a thing which required so long a time that the demand for roof prisms was largely filled by the time that they knew they could successfully do it-they dared not quit their regular jobs and make the leap. A second was the fact that a certain professional optician was able to convince authorities that amateurs never could make roof prisms. The man who accomplished this questionable end did so at a critical time when the nation's need for roof prisms has been described as desperate. At best he used bad judgment. At worst his outlook was constricted.

When World War III comes (compare with the history of Rome's three Punic Wars, in the third of which Rome virtually erased Carthage when Carthage was once more found to be rearming) let the amateur hit his optics early, hard, and unitedly, and with no inferiority complex.

SINCE Ferson, starting with average advanced amateur background (three mirrors, a flat, a lens), devoted three years of intensive concentration to optics and learned a lot which daily work of the same kind afforded frequent opportunity to check, this department recently invited him to write out for the benefit of other amateurs and professionals the boiled-down juice of his experience; and since two chapters in "Amateur Telescope Making-Advanced" (those on the Gaviola and Zernike tests) had aroused little interest since their inclusion seven years ago, these have now been replaced by a single 29-page chapter by Ferson, entitled "Prisms, Flats, Mirrors," in a new printing of that book. In the same printing Dr. John Strong has completely rewritten his chapter on mirror aluminization and has included in it some new and valuable working pointers. The book is still Edition 1 but is now the fifth printing of that edition, and is revised to the extent of a total of 39 new pages.

In his 29-page chapter Ferson gives the essential principles of prism manufacture for large- and small-scale production, also for hand production of small batches from a dozen down to pairs and singles-the singles being polished and corrected within annuli of plate glass for easier control by the tyro.

He gives a list of prism-making equipment and some dodges for avoiding too heavy investment on small jobs, compared with the value of the prisms.

He tells how to grind a prism to a close angle before polishing, a very pretty and labor-saving art.

He explains how prism face angles are tested.

He explains the exquisite art of correcting, freehand, the polished prism faces. This is the final process and the one calling for the greatest skill, but also is the most interesting one-rubbing off single seconds of are with a few simple strokes (simple if you know how!).

For prisms, flats, and mirrors, Ferson lays much greater stress on grinding than our art has ever called for before. His intensive experience revealed grinding to be just as important as polishing and no longer a perfunctory merely mechanical, preliminary process. The practical dividend from supergrinding is the avoidance of such ills as turned edge. Ferson thus pursued one source of turned edge into its hole and dug up the hole-found the basic principle involved and devised a remedy, a part of which includes the use of a channeled glass tool for grinding, a talc-emery mixture, and drying up the wets. One hour per stage also is now held to be too little with Pyrex.

The relation between prisms and flats may seem remote but actually is immediate: prism making is flat making. Prisms have flat faces but, even more to the point, they are blocked in batches in plaster matrices and thus are elements of a single big flat. Before the beginning of polishing, a flat can be ground within half a wave of the ultimate.

For polishing, Ferson finds that scratches are not attributable to hard laps.

He uses onion sack for sub-facetting and a rosin-pine tar mixture for the lap.

The main secret of success is the use of the dummy polisher for keeping the lap itself flat: the same dummy is used in keeping a lap dead flat for hand correcting prisms.

Ferson's work brought out the vital importance of correctly conditioning the rouge after applying it.

Some rules of heat effects are stated.

Finally, in his chapter, Ferson applies his prism and flat technique to mirror work, with the same channeled tool, same drying up of the wets, as precautions against turned edge inherited from grinding. But the dummy obviously can't be used on a non-flat surface. Mirrors are polished face up.

Not all these methods are claimed by Ferson; some are old. Mainly they are modifications of our amateur technique which protracted, intensive work brought out as more important than we amateurs had previously realized. Some of them seem radical, yet 11,160 roof prisms with an acceptance percentage of better than 99-1/2 seems to commend them. Proof of the pudding

Ferson now does professional work yet remains amateur at heart, still freely giving his experience to the fraternity, as in the new "A.T.M.A." Amo means to love. The amateur is one who works for the love of it.

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.