It is suggested that amateurs paste this picture in their copy of "Amateur Telescope Making." Had it been at hand when the new edition of that instruction book was in preparation it would surely have been included within the volume, which was originally built around Ellison's book, "The Amateur's Telescope" as a nucleus.

NOTHING but refractors are shown this month. So far as is known, these are all of the refractors that have been made since Ellison's unequalled instructions were included in "A. T. M." It is possible to make a refractor (of a sort) without due attention to the calculation of curves and care with other details, in fact many have been made from second-hand lenses previously used for other purposes. Henry Kawecki of Chicago (no street address submitted), a high school student, has made the one shown at left, using as the objective what he describes as "a lens which was once a mirror of planoconvex type from which the silver and paint were removed." The tube is three lengths of four-inch stove pipe and the eyepiece was taken from a microscope. Despite what some might regard as a doubtful type of objective, the maker states that he sees clearly Saturn's rings and Jupiter's moons, using 125 diameters magnification. "The chromatic aberration," he writes, "is not as bad as may be expected." He is now making a reflector.

Fred Caley, 5122 Hawthorne Street, Frankford, Pennsylvania, writes: "I enclose a photo of a refractor I recently constructed, thinking it might be of interest to the ever-increasing army of telescope makers. I used the second 92 formula given in 'A.T.M.' viz., three equal curves and a plane surface. Ellison states, 'The only snag is the plane surface.' I heartily corroborate his statement. The objective is 5-1/4 inches clear aperture and has a 76-inch focal length.

"The telescope is equipped with a worm gear, universal joint, and extension rod that can be worked without taking the eye from the ocular. Setting circles and a diagonal eyepiece are also fitted. Total cost, not more than 70 dollars."I previously ground and figured an eight-inch reflector which gave very satisfactory results. I also made a 5-1/2 inch flat and a couple of prisms, in order to gain experience. The refractor turned out much better than I expected."

Mr. Caley has obviously gone at this job right: after suitable preparatory experience of a practical nature-making mirrors, prisms and flats, all of which enlarges one's resourcefulness in optical work-he has tackled the more difficult objective lens job and succeeded.

A SIMILAR approach to the objective lens has been made by Franklin W. Smith, 407 Scott Avenue, Glen Olden, Pennsylvania, whose telescope is shown in the illustration reproduced above."After finishing my first reflecting telescope, which was described in your January, 1927, issue, I have made several small reflectors, and have recently completed a refractor," Mr. Smith writes. "The achromatic objective has an aperture of three inches and a focal length of 60 inches. Great care was taken while polishing the convex surfaces of the crown glass to prevent wearing down the centers excessively; in this way, positive spherical aberration was avoided, and it was therefore possible to finish the figuring, which was controlled by Ellison's ingenious 'auto-collimation test,' quickly and without difficulty.

"The color correction and defining power of the telescope seem satisfactory; double stars such as alpha Geminorum, gamma Virginis, and gamma Leonis are readily separated, even under the rather poor conditions of seeing which prevail here at certain times of the year.

"Although it takes vastly more time and labor to make a refractor than to make a reflector of the same aperture, the actual work is really no more difficult, assuming, of course, that the worker has had sufficient experience to enable him readily to produce a zone-free optical surface. I found that it required over four times as much work to make the three-inch refractor as to make a five-inch reflector. Not only are there four surfaces to work instead of one, but at least three of the four curves are much deeper than the single curve of the reflector. While rough grinding I soon came to the conclusion that the use of metal tools previously turned on the lathe to the proper radii would be a much more economical means of producing the deep curves necessary, since a glass tool grinds the edges as well as the center of a concave surface and the center as well as the edge of a convex, and much labor is needlessly expended.

"The auto-collimation test is as simple to apply as the ordinary mirror test assuming of course that a flat the size of the lens is available. I prepared the flat by the method given on page 37 of 'Amateur Telescope Making.'

"Since completing the three-inch refractor, I have been using it for observing variable stars. Under ordinary conditions of seeing it will show stars slightly fainter than magnitude 11. In this locality, the theoretical limit of a telescope can be reached on exceptionally good nights only. At least that has been my experience with the 10-ineh Clark refractor of the Haverford College Observatory."

The fourth refractor shown is apparently one of the synthetic type. The photograph reached us without accompanying letter and bore on its back only the name of the sender, Mr. George E. Stephenson, Roosevelt Avenue, Roosevelt, Long Island.- A. G. I., Tel. Ed.

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