"Several 12-inch reflecting telescopes have been made for the California Institute of Technology for the purpose of testing seeing conditions at the various sites being investigated for the location of the 200-inch telescope now in course of construction.

"The Pyrex mirrors for the 12-inch reflectors were figured in the optical shop of the Mount Wilson Observatory at Pasadena. The primary focus is five feet, but a Cassegrain focus is available which gives an equivalent focus of 20 feet. Eyepieces of 60, 320, and 480 power are used, the 'seeing' being judged by observing the separate of double stars, the diffraction pattern around stars, and the quality of the detail seen on the moon and planets.

"The mounting is of duralumin, the weight of the complete telescope being 235 pounds. It is provided with reading circles and slow-motion adjustments for right ascension and declination, and is driven by a clock actuated by a weight "

The photograph reproduced was shown to Russell W. Porter, designer of the telescope, who was induced to dictate the following additional comment: "The specifications laid down for this particular mounting were that it should be very rugged and stand rough treatment, as it was intended to be transferred from one site to another on the backs of pack mules or men, and to be easily separated into convenient units for packing. These considerations made it desirable that all delicate parts be enclosed, as far as possible.

"The entire mounting is of duralumin castings; the tube is of sheet aluminum the worm gear and adjusting screws of bronze. The only steel in the mounting is the lower hearing of the polar axis and the declination studs. These are chromium plated. The clock weights will drive the clock for 40 minutes before rewinding. The yoke, which is hollow, is especially rugged, and the declination arm and tangent screw are inside one of the arms. A slip ring at the upper end of the polar axis is divided into hour angles, allowing quick setting on any star in right ascension. Hand control in right ascension is by a removable key which engages the worm, whose end can be seen in the little hole on the base casting, just below the yoke.

"The cell holding the 12-inch primary mirror is fastened to the casting at the lower end of the tube by a threaded joint making about a half turn. This is not visible on the photograph but lies about halfway between the declination stud and the bottom of the cell. This method of attachment allows the mirror to be removed for safe keeping and to go back again to a positive stop, thus preserving the alignment.

"The whole instrument was painted a light gray with a dull finish and worked down to a beautiful white finish.

"The two telescopes were made by Fred G. Henson of Pasadena. Preliminary tests of the instruments on close doubles showed that the optical surfaces exhausted the resolving power."

THE number of spectrohelioscopes attempted thus far is disappointing. Perhaps the insertion of the series of sketches shown on this page, which gives a concrete idea of what the amateur may expect to see with a spectrohelioscope, may serve to, arouse further interest. These sketches were drawn from a solar prominence observed during the morning hours of June 19, 1930 by F. J. Sellers, F. R. A. S. and are reproduced from the Journal of the British Astronomical Association. Mr. Sellers points out that this prominence was not a large one, as prominences go, though it was very active. At 9 o'clock A.M. it had reached a height of about 30,000 miles, having risen at the rate of about 12 miles a second.

Seen through the spectrohelioscope these prominences are red and are a moving sight in more senses than one. There are plenty of them; Russell, Dugan and Stewart's "Astronomy" states that it is not at all unusual to find as many as 20 at once on the sun's limb. In 1916 (May 26) one was seen to reach the height of 500,000 miles, ascending at the rate of 20 miles a second. Can you imagine yourself sleeping late on a Sunday morning if you had a spectrohelioscope and could watch such stupendous cosmic events as these? Golf would not pull you away from the eyepiece, nor would motoring. No doubt when the dinner hour came your family would have to feed you forcibly.

FOR some months we have known that Professor George W. Ritchey had secured the necessary financial backing to begin work on a large telescope of the Ritchey-Chrétien type. He now has made this fact public. He proposes to build a reflecting telescope, of aperture not yet announced, and Miami, Florida, has been selected tentatively as the site. Robert Heckle, Gar Wood, the speed boat builder (who long has been an enthusiastic amateur astronomer), and other Detroit people are his backers. G. H. Lutz ("A. T. M.," pages 243-244) will assist him.

The Ritchey-Chrétien telescope was described by Professor Ritchey in a long series of articles in the Journal of the Royal Astronomical Society of Canada, beginning with the May-June, 1928 number. It has a short focal ratio and resembles a Cassegrainian except that, instead of a parabola and hyperbola, a combination of new curves is used. This does away with the distortion of stars not in the center of the field, from which all existing reflecting telescopes now suffer. He also plans to use curved photographic plates accurately ground and polished to a sphere of long radius, since the image projected by the mirror or mirrors of a reflector is not flat but is curved or "dished." He has developed several other extreme refinements, all of which if successfully compounded in one instrument should bring about a striking advance in the technique of telescope making and use. [These mysterious curves have been described-mathematically-in the Revue d'Optique (Jan. and Feb. 1922). How to put them on glass never has been described. Don't ask us; we don't know. We asked Professor Ritchey once and his reply was that it is "simple," but he did not describe the method.]

CHICAGO now has an organized group of amateur astronomers and telescope makers, so W. L. Dennis, secretary of the Pickwick Society, 4653 Addison Street, Chicago, has advised us. The Pickwick Society is an established amateur scientific organization but its telescope making activities are new. Its membership includes the professional telescope maker John F. Mellish and Professor Philip Fox, Director of the Adler Planetarium, who will act as advisors. The Society already has a seven-inch, two eight-inch, and a ten-inch reflector. Its activities will center in the Planetarium where meetings will be held. Mr. Dennis asks us to enlist the support of all amateurs in the Chicago district. We wish more power to the Pickwickian elbows. What city is next?

WE learn that the Corning Glass Works (Corning, New York) now has available some standard Pyrex sight glasses which happen to be quite suitable for telescope mirrors. There are several sizes: 6 by1/2-inch; 7-1/4 by 3/4; and 9 by 3/4. The prices are low. These disks seem pretty thin but should "get by" in nearly every case, as the 8 to 1 ratio usually specified allows a large factor of safety. They often contain bubbles but that can't be helped and these do little or no real harm.

TO complete this month's batch of odd items, here is one furnished by J. V. McAdam, Hastings-on-Hudson, New York. To avoid bubbles in a pitch lap, pour melted pitch on cold tool to half desired thickness and on face of cold mirror (first wet with rouge or soapy water) to equal thickness, and then lay the mirror disk on the other, pitch to pitch. Try it. Mr. McAdam also has modified the Rogers finder (see SCENTIFIC AMERICAN instruction book "Amateur Telescope Making," page 232) by inserting a monocular in the side of the tube, pointed at a second prism mounted within the tube and in line with the main prism where it intercepts no extra light. An ingenious wrinkle. Although it requires a larger prism, it reduces the number of outside gadgets on the telescope and renders the instrument less vulnerable.

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