PRODUCED on this page at 7/16 original size are several pages from Sir Isaac Newton's classic "Opticks" (1704). The selection begins at the fateful point where Sir Isaac made the famous mistake that led him just to miss discovering the achromatic lens principle-but also to invent and make the first Newtonian telescope. In it, the amateur telescope maker of today may see

Newton, himself essentially an amateur, at work on the first telescope mirror of record.

First-edition copies of Newton's "Opticks" are sold by rare book dealers at prices current from about $30 to $70. Let not the old-style of Newton's time dismay you, since after remarkably little reading it no longer trips you up.

The first complete sentence on Newton's 75th page begins on line 2 with the word "But," and contains the statement which delayed discovery of the achromatic lens almost a century. After a sketchy experiment Newton had jumped to the conclusion that refractive index and dispersion were proportional, so that by no two-component objective lens dodge could lenses be freed from chromatic aberration. The pundits long blindly accepted Newton's dictum.Plaintively, Newton next states that, so far as the reflector is concerned, he supposes people would simply have to go on using the same old principle, the one-lens objective of Kepler which had immense focal length to minimize aberrations, and obtain any improvements by still further increasing these focal lengths. But Newton goes on to say that users could at least avoid the long slender and cumbersome tubes which this had made necessary by using Huygens' new and really manageable mounting.

After finishing with Newton we shall return, in this antiquarian optical amble, to this new Huygens aerial mounting for which Newton puts in so strong a plug.

"I contrived a perspective," Newton writes on the same page. Old term for telescope.

The fraction on the same page, in tiny type even on the original, is 1/5. While, as Newton states, he stopped his aperture to 1-1/3", this was not the full diameter of his bell-metal speculum, which was 2-1/16". Even then his focal ratio became f/4.7, and it is remarkable that this gave performance, especially on a sphere-if it really was a sphere in the lack of a test. But any amateur knows the tendency with a soft lap to work toward the hyperboloid, and maybe Newton luckily landed squarely on the paraboloid without knowing it. He did know a paraboloid was needed, but neither he nor anyone else knew how to figure one.

The bottom line on page 75 refers to a refractor, obviously a Galilean type.

Page 76, line 6, mentions "overcharged." Empty magnification. Beginners still cry for it.

Line 8, "two of these." Of the two telescopes only the second, too often mislabeled the "first," survives. It is at the headquarters of the Royal Society of London, where your scribe once was permitted to examine it. The treasure was perched atop a cabinet at eye level, entirely in the open but in private office quarters. The accompanying photograph was obtained at that time.

The competent workmanship clearly proves that Newton was himself a good amateur telescope maker and mechanic and there is record that he bought a lathe while at Cambridge University. On that lathe and with his own hands he must have turned up the wooden base, the cup and ball mounting so simple and ingenious, and the eyepiece shell.

Newton made these two reflectors respectively in 1668 and 1671 and, since they were approximately alike, the question whether the one that survives is the first or the second is, after all, of lesser moment. He and others in 1674 communicated several items concerning them to the Royal Society through its periodical (still being published) the Philosophical Transactions. He did not write his book, "Opticks," until about 1687 and then delayed its publication until 1704.

There are replicas of Newton's telescope in the planetariums in Philadelphia and Chicago and in the Buffalo Museum of Science. As a pure sporting proposition, any modern amateur who makes a copy of Newton's telescope might at least consider the whim of foregoing those advantages which Newton could not enjoy, which would prove to be more than at first appears, and afterward ascertaining whether his work would pass the test to which Newton put his telescope. "I found," he writes "that I could read in the Philosophical Transactions, placed in the Sun's light, at an hundred foot distance, and that at one hundred and twenty foot distance I could discern some of the words.

Page 76, "as thin as a groat." Your scribe caught up with a Henry VIII groat at the Scott Stamp and Coin Co. and, though not much worn, it was very much thinner than a badly worn dime.

"Putty" is tin oxide.

RETURNING now to the old long-focus, one-lens Kepler refractors, typical examples of its kind are: 3" lens, 30' f.1. (f/120), 5" lens, 100' f.1. (f/219); 7-3/4" lens, 200' f.1. (f/258). The long, slender, floppy, shimmying-tubes were skeletonized and braced laterally by spreaders and hung on multiple bridles from tall poles, but in his new aerial mounting Huygens substituted for all this cumbersome gear one single simple silken cord of seven-pound strength (finest modern bait casting line nine pounds test-Abercrombie and Fitch). This line alone linked together and controlled the objective in a delicately counterpoised cell on a ball-and-socket, pivot, and the eyepiece.

Details show in the accompanying illustration from Smith's "Compleat System of Opticks" (1738). A little crook in the tail of the cell stick offsets the angle of sag (sketch 614) of the line. Sketch 615 shows the large eyepiece on a stick, the line and its guide, also the violin peg adjustment for f.1. (The scissors-like part is a variable rhombus attachment on a rest, by which a star, once found, could be held long enough to enable an inexperienced observer to get to the eyepiece.) Sketch 616 is a Mr. de la Hire's lens cell control.

The whole, after study, ceases to seem ludicrous.

SOME years ago, in the Proceedings of the Royal Society of Edinburgh the astronomer Sampson and the famous professor of optical design Conrady, with R. Westlake, today professor at the University of Rochester and lens designer for Eastman Kodak, examined, tested, and described three of these old one-lens, long-focus objectives preserved at the Royal Society of London. One was a 7-7/8" of 122' f.1., diamond-signed by Huygens in 1686, together with the original apparatus for adjustment of his aerial telescopes, including eyepiece of 2-1/4" aperture and 6" f.l. The second was an 8-3/8" of 170' f.1., signed by Huygens 26 June 1686 and later owned by Newton. The third was a 9-1/8" of 210' f.1.

These examiners reported: "In comparison with even the cheapest of modern window or bottle glass, that in Huygens' lenses is extremely bad. Besides numerous bubbles and small stones and frequent black particles considerable size . . . the entire dish are simply one tangle of innumerable mostly fine veins which would render really regular refractive effects quite impossible." The refractive index for the 170' was 1.53, for the 210', 1.58, corresponding to modern plate.

The plano side of the 210' was found to be "amazingly close to flat." Centering was precise within 0.0016" and 0.0056", yet Huygens centered by milking lens edges with a hand vise.

The two authors add: "There is widely current misapprehension in the matter of achromation in relation to these early systems. If the ocular is also a single lens and mate of glass of the same dispersion, then for the combination, focused to infinity, the angular magnification is measured by the ratio of the focal lengths, and from this ratio the refractive index of the glass eliminates itself and leaves a function of the curves alone. Hence the image would be achromatic. The case is not so simple as this because the combination cannot be focused to infinity simultaneously for different colors, but a good approximation to it may be reached by focusing in the orange-yellow. We conclude," say Sampson and Conrady, "that the chromatic faults of these combinations were less noxious than is generally believed."

Suppose a Kepler-Huygens aerial telescope were today or post-war made and set up beside a Newtonian of comparable aperture as a demonstration, what widespread attention it would attract! Utility, low. Scientific demonstration value, interesting, somewhat instructive. Such stunts should, however, be done for the fun of it-justification enough.

A few possibilities, from a table of Huygens' standards, are: a 5.48" of 100' f.l., hoisted up and down on a 75' pole, eyepiece 6.03" f.l. Or a 3.87" of 50' f.l with 4.26" eyepiece and a 40' pole.

Specific directions for ordering from large libraries photostats of the Newton, Smith, and Sampson-Conrady writings, giving working data, are available from this department.

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