BOSTON, traditional home of the bean and the cod, is said to have slipped somewhat in beans, but in telescope making it has come up a long way since the organization, some years ago, of the enterprising Amateur Telescope Makers of Boston. Leading spirit and first president of this organization has been W. H. Hargbol, 600 Beech St., Roslindale, Mass., (a postal station in Boston), and this column has too long been remiss about describing Hargbol's telescopes, three of which are shown in Figures 1, 2, and 3.

Hargbol began, some years ago, the same as any typical amateur, by making a modest first telescope, and the rest simply followed as usual by a kind of internal compulsion: he has now worked, he says when questioned, on 125 to 200 telescopes for himself and others, and he instructs in formal university extension classes at Harvard and at the Franklin Union Technical Institute. He does all his mirror work by hand.

Figure 1 is an 8", f/6.5 portable, with brass-covered galvanized tube.

Figure 2 is a 10", f/6.2 portable, with a tube of 3/32" Bakelite. This is attached to the declination axis spider casting by means of two long rails. These in turn are attached to two end brackets screwed respectively to the cell and to the central tube ring, so that the tube itself does not touch any of these except the ring and cell.

As Figure 2 shows, nearly half of the total tube length lies above the central ring, and this part may be rotated, the ring shown being divided in two parts. Hargbol was warned in advance that such a long rotated tube end usually is difficult to maintain in accurate geometrical relation to the lower end, and causes adjustment troubles. He therefore saw to it that the rings received very fine machine work, and found that the extra pains taken paid well, since the arrangement has proved good. Both rings are essentially L-shaped in cross-section, the lower one having an inner, upward projection. In addition, there are six external clamps, held on by screws into the lower ring, and, between the retaining projection and the clamps, the tube end does stay where it is told to stay.

The polar axis is a solid piece of 1-3/4" steel, the declination axis l-1/2". Both have thrust ball bearings.

Figure 3 is a 12-l/2'' reflector with an f/5 Pyrex mirror. Figure 4 is its focogram with very good shadows-for a short focal-ratio mirror. Since there is perennial evidence that, despite warnings in the handbook, "Amateur Telescope Making," many beginners, not to speak of some who are not beginners, are satisfied to judge a mirror merely by visual inspection of the shadows without actually measuring zones; and since this practice is very likely to lead to the production of over-corrected mirrors, some of them grossly so, readers are warned not to take away with them as a mental standard of shadow density, for application to the average mirror, the shadows of this focogram. The shadows are right for this f/5 mirror but would be wrong for the average mirror with medium focal ratio. Ellison emphatically points this out in "ATM," page 96. The mere distribution of lights and shadows on a mirror is not an adequate criterion of the radii of its respective parts. This point is twice labored here for the benefit of the increased number of younger men-18 to 22-who are known to be taking up telescope making today. We have evidence that good mirrors are becoming fewer and farther between, and some think the two facts are related. Middle-aged men are more tenacious and patient, and less inclined to be in a big hurry, and therefore they turn out better jobs. Hence, measure zones-don't merely hope, even if the shadow map looks right. Looks are deceptive; mirrors, too, wear make-up. And refigure, even if it hurts, when the map looks fine but the curve proves to be too deep. On an f/8 the shadows will be much greyer and thinner than those of Figure 4.

The 2" polar axis shaft of Hargbol's 12" telescope is mounted on a tapered roller bearing at top and a ball bearing at bottom, the bearings packed in grease and provided with dust covers. The photograph shows the wide, thin fins cast integral with the declination axis casting, making it very stiff-practically as stiff as it would be if the entire envelope were solid, yet much lighter. Hargbol made the patterns and core box and will be glad to pass along to any interested amateur the experience he gained in doing this part of the job.

The triangular spider at top of the declination axis appears in Figure 3 to have an open center, which would mean weakness, but actually it is a casting having a strong central web.

The base casting of this telescope weighs 40 pounds, the declination casting 25 pounds, the tube base weighs 15 pounds, and the counterweight 56 pounds.

TRAUB, not Pope, as stated, was the maker of the observatory dome shown in the October number on page 234. Pope writes to say that he doesn't want credit for another man's work. Ours was the error.

TED WATTERSON, official photographer at Palomar Observatory, Palomar Mt. (Yes, it's now a United States post office), Calif., made the two photographs of the 200" telescope shown in Figures 5 and 6.

Figure 5 shows the upper end of the tube, 20'3" in diameter, cuddled down into the big horseshoe, 46' in diameter, which constitutes the north bearing, and pointing toward the celestial pole. The two oil pads on which the horseshoe floats as it rotates show at left and right. Figure 6 is a close-up of one of these unique pads. Oil is constantly pumped into these pads under pressure. This cuts the torque required to rotate the telescope from 22,000 pound-feet as calculated for roller bearings, to 50 pound-feet. The oil comes up through holes. The pads are covered with babbit metal. The entire pad rests on a knife-edge and each half rests on a spherical seat.

The horseshoe (split ring) bearing is a Porter contribution.

BUBBLES in Pyrex mirror disks cannot be entirely avoided, because Pyrex remains so viscous at temperatures to which it can be raised in melting (about 2800 degrees F.) that the smaller ones haven't enough flotation power to push upward to the top and escape. The manufacturers therefore have to cull the disks over, throwing out the more bubbley ones. Recently, we learn, they have been culling these disks more closely.

If, when the disk is ground, the grinding intersects bubbles, a thin edge is usually created and any fragments breaking loose may scratch the glass. Different amateurs have used various methods of anticipating these troubles and heading them off in time (when the first break-through occurs) by reaming them out. Our file on this subject shows that M. J. Ireland, Dearborn, Mich., used a twist drill and abrasive grains. Edward P. Woodcock, Long Beach, Calif., used the rear end of a twist drill or a rattail file with abrasive grains. Lew Lojas, New York, put a round-head screw in a drill brace and similarly used abrasive grains. Woodcock further commented: "Because the bubbles do not materially affect the surface optically, they can do little harm if left alone, provided the edge looks safe from chipping, as in cases where they lie perpendicular to the face."

H. H. Selby, of California, after having some perplexing difficult with mysterious scratches, found bubbles to be the cause. "After each wet," he says, therefore, "I dried the surface, scrubbed the bubbles hard with a toothbrush and shellac and, after ten minutes, scraped off the excess. During this scrubbing, the brush broke the thin edges of the glass and the shellac sealed in the fragments."

INVENTION of the telescope is generally credited to Jan Lippershay, who in 1608 arranged a convex lens in front of a concave. Bell, in "The Telescope," says Lippershay's telescope was far, however, from being an astronomical instrument. In the following spring Galileo heard rumor of this instrument that made distant objects seem near, sat down and, in one evening, independently figured out an arrangement of lenses which would accomplish this end and it magnified three diameters. Galileo, as Bell states, soon developed this crude beginning into a real instrument of research, magnifying 32 diameters. This telescope is on display in a museum in Florence, behind glass, and your scribe in 1928 slipped the guard there 50 cents to open the case and place a step-ladder before it, so he could climb up close for a little veneration at this fane. Main credit for the invention of the astronomical telescope rightly goes to Galileo; he (1) really made something of it and (2) did important research with it. Moreover, Galileo, not a meek man, fought for his discoveries and gave them publicity, when he could have kept out of hot water merely by being tactful and o agreeable This probably had very much to do with their survival.

While visiting the exhibition of the scientific achievements of Leonardo da Vinci, described on page 332, with Russell Porter, your scribe stumbled on the two grinding machines shown in Figures 7 and 8. If Galileo, who lived from 1564 to 1642, gave us the first astronomical telescope, what was Leonardo da Vinci, who lived from 1452 to 1519, or roughly a whole century earlier, doing with these designs? Porter and Ingalls looked at one another and remarked, "What does it mean?" Were the histories of science then all mistaken? "Better look into that," said Porter, and took a train for California.

The machine in Figure 7 was accompanied by a label stating that it was "a model of a hand-operated machine for grinding a concave lens for a telescope or other instruments." The radius beam on the one in Figure 8 bore the label, in Italian, "Leonardo made this up to 12 meters long." The first machine has a stub lever beneath the bed-plate, with a notch on which a weight could be hung to hold the disk against the grinding wheel just as it is shown in the photograph. The remainder of the mechanism is obvious. (While the lantern gear may look antique, be it remembered that in Leonardo's time a man couldn't simply turn to the Chicago or Boston Gear Works catalog and select a gear; he had to make his own. Moreover, some of these old gears were not so inefficient as one might think.) The machine in Figure 8 is crank-operated (crank at right-hand end removed in photo) and causes the convex metal sector on the nearer end of the long radius beam to traverse the disk. Evidently the crank man must go into reverse after each two or three turns.

At the offices of the New York Museum of Science and Industry, it was learned that Prof. Georgio Nicodemi, Director of the Department of Fine Arts of the Common of Milan, also Director of Museums in Sforza Castle and an outstanding authority and writer on Leonardo, had accompanied the exhibition to New York. When hunted up and questioned, through an interpreter, he said that the question of Leonardo's possible priority of invention of the telescope had been the subject of recent discussion in Italy, and he kindly offered to prepare a note summarizing these discussions.

It appears that Prof. Claudio Argentieri has discovered some pages of Leonardo's original notes which have not yet been published. "The most surprising of Argentieri's observations," Prof. Nicodemi writes, "are those concerning the telescope. On folio 25T, of Codice F, which is now in the Institute of France, in Paris, Argentieri noticed, under a figure of a large tube mounted on a stand, the words, 'This eyeglass of crystal must be flawless and very clear, and is to be thin in the center.' The note obviously refers to a negative lens. Other notes on the same sheet leave no doubt that Leonardo wished to design a magnifying instrument, and still others explain that one lens was to be plano-convex. Brief writings in Codex E and Codex A [exact references available to any interested reader.-Ed.] indicate that Leonard intended his telescope for astronomic applications."

Prof. Nicodemi goes on to state that Leonardo improved his telescope by using a concave mirror with a catacaustic curve but without an eyepiece. The machines shown in Figure 8 might have been used for roughing out such a mirror.

Since Leonardo couldn't have used a concave lens alone as a telescope, though he could use a convex, it seems possible that he had used the two in combination-that is, the arrangement now known as "Galilean;" apparently he also used a concave mirror without eyepiece. But in any case, he omitted to publish an account of his telescopes, thus losing credit if this were his due; incidentally, delaying availability of the telescope to the world for about a century.

Whether this would have opened up man's cramped horizons in Leonardo's times, as it later did in Galileo's, and accelerated the Age of Science as much, is, of course, a question. Our guess is that, today, the 200" telescope would be a back number.

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