"I became interested in making a telescope through watching my husband make his 9" Newtonian. In the beginning I had no thought of making a compound telescope, but gained my first practical experience by grinding and polishing a 6" mirror made up of layers of wind shield plate, which, true to what has been said of its type, proved in the final polishing not to hold its figure.

"My husband supplied the tube and mounting, the latter being of pipe fittings welded to a fly-wheel as a base. The eighteen sided wooden tube is made of lattice strips.

"My primary mirror is 8" in diameter and is pierced for the Cassegrainian and Gregorian set-up. The Newtonian focus is slightly over f/4-1/2. The Gregorian secondary is approximately 10" from the Newtonian focus. I ground, polished, and figured both mirrors, also ground and polished a pair of plano-convex lenses for a Ramsden ocular of approximately 2" e.f.l. The finder was made of reading glasses of the pocket variety.

"As it could be figured directly without the primary, I completed the Gregorian secondary first.

"My Gregorian is somewhat difficult to keep on a star, but I have spent many enjoyable evenings with it. I get sharp, beautiful detail on the moon; and Saturn's rings, Jupiter's zones, belts and satellites, as shown by the telescope, are of never-ending fascination to me. The making of my telescope has not been easy. At every phase of the procedure I experienced the telescope maker's usual troubles. What I do not know about optics would fill many a book, but that I have, by the liberal use of 'Amateur Telescope Making,' been able to fashion a workable instrument, gives me considerable satisfaction."

CEMENTED skeleton glass disks may or may not hold their figure. Often, when they do, it is difficult to ascertain whether the front disk held its shape without actual aid-the other parts then being mere excess baggage-or whether an actual structural limit has been created: In ATM, p. 308, there is a note bearing on cemented disks. Thomas A. Martin, resident at 126 Monroe Ave., in the famous Wisconsin center of gravity of the overall industry (see Figure 2) says:

"I am sending you a picture of my latest telescope. Total cost, $15. The mirror is made of two 12-inch disks, five-eighths of an inch thick, cemented together with 12 glass blocks between. It took 16 hours to complete the mirror with what I think is a pretty fair parabola.

"The mounting is constructed entirely of used two-by-sixes-very inexpensive but remarkably stable. The whole thing rolls out of the garage on four bed casters. The tube is made of 22-gage iron. The top 18 inches, holding the eyepiece, can be turned to the most comfortable position."

Having gone so far as to equip his telescope with bed casters, the maker may have missed a trick in omitting the bed itself- especially as the bed of the mounting has just about the right proportions to receive one. Seriously, R. W. Porter, years ago when working out the indoor telescope shown in ATM, at V on p. 51, tried to arrange it so that he could use it from bed. This would be the very summum bonum in telescopes and the problem is passed on to others who may care to lie abed and expend gray matter on it.

WHATEVER a man designs and makes, brings his own inner character tangibly and visibly into the open where all may inspect it. Some amateurs' telescopes are roughly designed and inefficient, others roughly designed but efficient; still other are smooth in appearance but mechanically lacking at some vital point or points, while a few are both well designed and easy to look at. The one shown in Figure 3 was noted at the Stellafane convention, where it was brought last summer, because it seemed to fall in this fourth category, and the following data were given by its maker, Philetus Allen, 45 Sheridan St., Glens Falls N. Y. It is a 6" and has heavy axes, the PA being 1-15/16" and the Dec. axis 1-11/16" in diameter. The heavy base casting weigh 105 pounds and is of solid bronze-a beautiful metal. Allen made his own pattern. Th main ring around the tube's waist is 6" wide and 5/8" thick and is of solid bronze, as are the two end rings. The tube is finished in antique bronze. The whole job has a sleek clean appearance-good taste, both mechanical and aesthetic.

Figure 4 shows the adjustable eyepiece rack which carries with it the prism mounting-an old idea but an efficient one, cleanly worked out.

SMOOTH also is the 7" Cassegrain shown in Figure 5, the optics by A. Priselac, the machining by Emir Kelly, members of the Amateur Telescope Makers of Pittsburgh. "This one really works as nicely as most refractors," we are told by Leo J. Scanlon-"splendid definition, smooth mounting, professional touches."

AMONG amateur telescopticians (isn't that at least as good a word as mortician?) there is a group having an interest in clock drives, and a more or less refined mathematical interest in gear trains that will split fine hairs in accuracy of time keeping. E. C. Stanton, Washington, D.C., writes:

"How's this for a polar axis telescope drive? Starting with 1 revolution per minute, given by any clock motor, the drive shaft connects with a gear of 44 teeth, meshing with another with 179 teeth on a worm shaft, the worm wheel is on the polar axis and has 353 teeth. This mechanism will rotate the axis in 1436 3/44 minutes, equal to 23 hrs., 56 min., 4.091 sec., which is the length of a sidereal day to the last decimal place given in the Ephemeris. In a tropical year of 365.24219879 days the axis would be revolved 366.24219721 times, an error which amounts to 1 degree in 1760 years.

"This is offered to your fans with my compliments-and a challenge to beat it in accuracy."

Of course, at this point or sooner, the question becomes mainly one of the pursuit of the ultimate for its own sake rather than a practical one, but even this is of much interest to those who enjoy refinements of method. Hence we reprint a part of a letter which appeared a year ago (Nov. 28, 1936, p. 931) in Nature (London). Its writer is the same F. Hope-Jones who is prominently, mentioned in ATMA in connection with the Synchronome clock (pp. 427-446), and it looks as though the Dr. Comrie mentioned in it, a mathematical astronomer at the Greenwich Observatory, had beaten the challenge mentioned above, even before it was issued.

"The problem involves the precise expression of the ratio between the sidereal and mean time in the form of a train of gear wheels. Since one mean solar day is 24^h, 03^m, 56555 36^S in sidereal time, the ratio of sidereal to mean is 1002 737 909 3....This ratio must be expressed by a fraction; for our purpose the numerator and denominator of this fraction must both be factorizable into factors not exceeding a few hundreds, as the number of teeth on any wheel cannot reasonably exceed this. Moreover, the number of factors (or suitable combinations of them) in the numerator and denominator must be the same, as wheels must work in pairs.

"The first to accomplish it was George Margetts, a member of the Clockmakers' Company circa 1800. It is in the form of a large watch and is to be seen in the Company's collection in the Guildhall. It has separate dials for hours, minutes, and seconds, each having a smaller dial mounted concentrically with the larger ones. These inner dials were gradually revolved backwards by gearing, so that the same three hands indicated simultaneously mean time on the outer dial and sidereal time on the inner dial. His train includes a wheel of 487 teeth so fine that they are invisible to the naked eye. The ratio is 1002 737 85, which is correct to the sixth decimal. The sidereal component would lose at the rate of 18^S in a year.

"In the Science Museum there is a clock designed by Joseph Vines a hundred years ago (1836), with two dials coupled by the ratio . This is 1002 737 915 4, which is correct to the seventh decimal. It will lake 5.2 years for the sidereal dial to be in error relatively to the solar dial by one second.

"Paris adopted a train by Ungerer, of Strasbourg, , which is 1002 737 905 4, and correct to the eighth decimal; it will be 82 years before it is a second wrong.

"Sir George Airy contributed to the Monthly Notices of the Royal Astronomical Society in 1850 a train by Dr. Henderson, , a ratio of 1002 737 908 5. This is very close, being correct to the ninth decimal, and requiring 40 years to accumulate an error of one second.

"At this stage of the investigation, I was fortunate in interesting Dr. L. J. Comrie, who, as a result of 'a pleasant week-end's arithmetical recreation,' summed up the whole matter and contributed a solution which we may accept as final. He gives the true ratio as 1002 737 909 265, plus the centennial term, and a wheel train of , which is the value of the precise ratio required in the year 1955, namely, 1002 737 909 297. The error would amount to one second in about 100,000 years."

At this point hard-headed extraverts who may consider all this sub splitting of ultra microscopic hairs a trifle over-refined for US mere amateurs with plain back-yard telescopes which may or may not even sport an alarm clock drive are entitled, if they wish, to offer the yarn about the Yankee salesman who was working hard on a western farmer trying to sell him a cornsheller. At great length he urged its purchase but the farmer, throughout the sales talk, wore a puzzled expression; and finally, when the torrent weakened a bit, he manage to say: "Yeah, but what's the purpose of it?" Came the reply: "Why, man, think of all the time it will save your hogs in eating." His eyes at last brightening up with a sudden in inspiration of understanding, the farmer answered: "Haw haw! What's time to a hog? "Nevertheless that outstanding one second in 100,000 years is a challenge to all mathematically-minded introverts. It's scandalous!

When the above letter was first published in Nature the London Times stated that "A new clock whose error is only one second in about 100,000 years is described in Nature by Mr. Hope-Jones." The Astronomer Royal soon pointed out that one second a year was the clock record, and that there was no actual clock of that refinement, the calculations merely tell what could be-if other sources of inaccuracy did not far outrank this one.

ONE function of this telescoptical columnist (or telescoptimist) is to keep a weather eye on scientific journals of limited circulation, and reproduce here items from them that may interest other amateur telescopticians. Hence another letter from Nature (Aug. 21, l931, by Dr. James Weir French, of Barr and Stroud, Ltd., optical manufacturers, Glasgow, Scotland:

"It is not generally known that by a simple device so-called optical contact can propagate itself.

"Contact is usually produced by the application of considerable pressure, first on the center of the plate and thereafter in a spiral path outwardly to the periphery. If, however, the test plate is pierced by a small hole and pressure is applied at one point and then withdrawn, the surfaces, without further manipulation, will move together into optical contact.

"In Figure 6, A is an optically polished glass disk, lying upon a test plate B, pierced by a hole C. Pressure is applied, say, at F, and then withdrawn. The Newton rings around the point, without further assistance, expand and disappear, leaving the surfaces in pseudo-contact and in darkness devoid of colors. A small speck of dust, such as D, will not arrest the movement. It is interesting to observe the rings at E attempting to encircle the speck and ultimately doing so, leaving around it two small bluish white rings, separated by a mottled dark one. These white rings suggest the following explanation of the phenomenon under consideration:

"Optically polished glass surfaces, unless they are specially treated, have surface layers of something akin to grease. Pressure at F bends the plate A sufficiently to join the grease films, as at G. Surface tension forces around G expel the air and extend the liquid continuity over the whole surface. Light falling upon the area G passes through more or less completely, according to the equality of the refractive indices of the grease and glass. Viewed from above, the liquid region G appears dark and, from below, bright.

"Light is reflected from the rounded surface tension contours, which regions appear bluish white. Newton rings may appear in the remainder of the area, From measurements made by Sir Isaac Newton, I reckon the thickness of each grease layer to be less than one millionth of an inch."

HOW many of the more recent amateurs have ever heard about the Porter Garden Telescope? Figure 7 shows one of these handsome decorative bronze mountings. About 1923, when R. W. Porter was optical associate of the Junes and Lamson Machine Company, in Vermont, and before this magazine had adopted the infant amateur telescope making hobby, he designed, made, and his company sold, 75 or 100 of them. They had 6" mirrors and were f/4, and sold for 400 dollars. Many of the mirrors were figured by a local lad named Wilbur Perry, whom Porter trained to do this work, and he took to it like a duck to water. Later, Perry took a position making diffraction gratings with Prof. R. W. Wood of Johns Hopkins, and is doing that ultra-skilled work today. For the Garden Telescope Porter employed his split ring equatorial principle which has been adopted for the 200" mounting. None of these telescopes are to be had today, in case any reader suspects this of being a subtle advertisement. The irregular swelling of the spinal column is a representation of a leaf, and another leaf swings down under the mirror and part way up again. These were handsome instruments.

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