"Reference to the picture [page 176.-Ed.] will show the dome which houses the 101/2" Pyrex reflector, in the lower right hand part of the picture. This instrument is carried by a Bruce type mounting and is used with many different combinations. Quartz secondaries provide for focal lengths of 200", 540" and 850". A 6", f/6.5 Petzval lens, which is often mounted on the side, provides speed and wide angle.

"Early in 1932 work was started on an instrument which wechristened the 'spectroheliokinematograph'. Essentially this instrument is a spectroheliograph plus a motion picture camera and such an instrument makes it possible to photograph solar phenomena in the light of some chosen wave-length or element alone. The addition of the motion picture camera has made it possible, for the first time, to secure continuous records of solar phenomena. The spectroheliograph has for its optical train a Littrow type spectroscope employing a 4" Ross collimating lens of 72" focal length. This lens was designed by Prof. Ross and made especially for this instrument. A 4" grating, 20,000 lines to the inch, is in service at this time and the spectroscope, plus the camera, is mounted on the 10-l/2" equatorial telescope. Those who are interested in detailed descriptions are referred to the various publications of the University of Michigan Observatory" [usually available for consultation at the different professional observatories, but otherwise difficult, at this date, to obtain.-Ed.]

In describing the new solar tower, McMath writes: "If the reader will refer to the accompanying line diagram, it will perhaps be easier to follow this description. Experience has taught us that there is no substitute for mass in designing a photographic telescope. Consequently, all parts of this instrument are very heavy. As an illustration, the combined coelostat and flat mountings will weigh a little over six tons.

"Our dome on the solar tower is 17' in diameter inside, and the effective shutter opening is 4'. We used a standard water tank bottom for this dome and cut the shutter opening out with a torch. The base ring is an 8" x 6" x 1/2" angle and the weight is carried on eight rollers, spaced at 45 degrees. An additional eight spacing rollers keep the dome concentric. Construction is entirely of welded steel.

"The outside shell is 17' in diameter and the inside tower is 6' in diameter. Each tower is supported on its own columns and the foundations for each set are separated. Optical tests made show that no vibration is transmitted from the outer shell to the inner tower, which carries the coelostat. The workroom is 28' in diameter inside the octagon, giving ample space in which to work.

"Entrance to the spectroscope pit is through an underground photographic dark room, which will be provided with water and necessary equipment. The pit is 7' in diameter and 30' deep. It has an inner steel lining which was welded water-tight. This pit houses the spectroscope and is provide with a steel cage 2' square, of which about two thirds is carried on the bottom bearing and the remaining one third on the upper hall bearing in the pedestal. The pedestal at ground level, is 4' high and the actual net working surface of the rotatable pedestal top is a circle whose diameter is 52".

"The coelostat mirrors are of optical Pyrex. The first mirror is 22" in diameter and 5-1/4" thick. The flat is 18" in diameter and also 5-1/4" thick. Sunlight passes through the shutter to the coelostat mirror, thence to the flat mirror, and then straight down the inner tower to a 12" parabolic mirror of 20' e.f.l., at the pedestal. This mirror is figured off axis, and returns the now converging beam back up the inner tower to a 9-1/2'' Pyrex flat [Note bracket.-Ed]. This flat reflects the converging beam to its focal point on slit No. 1 of the spectroheliograph. Provision has been made at this point for the use of a 16", 40' e.f.l. mirror to give a larger image of the sun.

"Light from the first slit of the spectroheliograph travels down the pit inside the cage to the collimating lens. We expect to use either a 15' or a 30' spectroscope, as the need may arise. This diverging beam passes through a 6" clear aperture collimating lens and falls upon a 6", 15,000 line plane grating. Light of the desired portion of the spectrum is returned by the collimating lens to the second slit of the spectroheliograph. The camera is, of course; focused on the second slit. These slits are arranged to move in opposite directions at exactly equal speeds and the resulting picture is a spectroheliogram taken with light of one wavelength.

"The coelostat and motion picture camera will be driven by the present equipment located underground, to the northeast of the 10-1/2" dome. All other slow motions, driving rate controls, chronographic recording, mechanism for controlling ratio of light to dark time on the motion picture film, and so on, that have been found essential in our previous work, are also electrically controlled in the new tower by merely extending the electrical circuits from this underground control room. Our method of driving and controlling equatorial telescopes has been described in the Publications of the University of Michigan Observatory. Space prevents a detailed description at this time, but it may be said that the reason for building a solar tower at this location is because of the fact that the existing equipment can be used in toto.

"Some years ago the entire observatory was given to the University of Michigan and is now operated as a branch of the University of Michigan Observatory. It has been financed entirely by private gifts. If a satisfactory example of an amateur is an individual who fails to make money following a hobby, then the present director and staff are amateurs de luxe

All of our equipment is 'home-made,' and has been built from designs made largely by the present director. The mounting and so on have been made by the Motors Metal Manufacturing Company of Detroit, the steel work and so on by Whitehead and Kales Company of Detroit and, with the exception of the two large mirrors for the coelostat, the optical parts are from J. W. Fecker of Pittsburgh, Pa. The two coelostat mirrors are being figured by the Warner and Swasey Company of Cleveland Ohio "

The spectroheliokinematograph describe above by McMath and shown on the opposite page consists of a metal box weighing 70 pounds containing a modified (shortened focal length) Hale spectroheliograph and 35 mm. motion picture camera. Anderson prisms are used, and are driven by a small air turbine. A day's photography of the sun consists of about 600 separate spectroheliograms, and these give a motion picture when run off rapidly. With the solar tower equipment as many as 720 exposures per hour will be obtained.

THE following is a suggestion made by J. R. Haviland, 426 Second Ave., Lyndhurst, N. J., under the heading "Things to Try." Perhaps someone will try it out. " A German patent formula for preventing tarnish on silver (used on silverware) might be tried out on silver films. Solution of potassium chromate in water. Immerse silver at room temperature 5 to 10 minutes. The very thin layer of silver chromate formed is transparent and protects the film. May not work on a mirror."

SOMEWHAT belatedly we have run across an article on "nervous breakdowns," in the April, 1935, number of Fortune. This states that telescope making is being used as "occupational therapy" at a mental sanitarium in the mid-West. Whether it will help the patients or drive them quite crazy is something of a question. Perhaps the wives of those who read this department and follow the hobby will throw pertinent light on this matter.

"Starting at the floor, you first see the 2 H.P. motor that drives the 'Hyvac 100' pump, which is right back of it and is only partly visible. It gives a final vacuum of 3 x 10^-5 mm. of mercury. Above this is the heavy reinforced steel plate upon which the steel 'jar' rests. The steel jar with its ports may look like a Buck Rogers contraption, but the extensions are merely to keep the aluminum vapor from reaching the glass ports. There is approximately 18,000 lbs. pressure on this jar when exhausted, but it stands up O.K. In the rear you will see a small steel jar which I use for small mirrors and special work."

Perhaps others who do evaporating will send in similar pictures.

THE following communication, entitled "Science and Facts," has been received:

"So-called modern science teaches that the earth revolves or rotates on an imaginary axis every 24 hours; and that the sun is stationary; and that the earth whirls around the sun once a year. It also claims that the sun is a larger body than the earth, and that the sun is 93,000,000 miles from the earth.

"It can be proved by more than 100 different facts that this is all nonsense and imagination.

"In the first place, the earth is too large and too heavy a body to be able to rotate or to revolve. Such a movement would also be perpetual motion.

"It would also be impossible for the earth to rotate or to revolve evenly and regularly, on an axis, every 24 hours, as the axis would sooner or later wear away, thereby causing the earth's poles to become lopsided, which would then cause the earth to rotate or to revolve unevenly and irregularly.

"It would also be impossible for us to live more than a few minutes, with the earth traveling at such a speed as 1000 miles an hour, as we would all soon suffocate. And it would also be impossible for the clouds, traveling at the rate of 40 miles an hour to catch up with the earth. It would also be impossible for the sun to heat and warm the earth, with the earth traveling at the rate of 1000 miles an hour, as the earth would soon freeze up solid in a few days."-W. J. BARTH, Howard Lake, Minnesota, Authority on Science.

Let Timken, S-K-F, Hyatt engineers install bearings that won't permit the earth to wobble.

THE dingbats shown above are combinations for using finders without added inconvenience. The one at the top was suggested by James Hart Wyld, 307 Foulke Hall, Princeton, N. J. The regular prism carries a finder objective on a bipod or bracket, and is rotatable against stops. The lower one is by M. C. Parks, Electric Vacuum Cleaner Co., Cleveland, Ohio, and, like the first, explains itself. In both cases the prisms rotate.

HERE are some solid data from Horace n H. Selby, a chemist, of San Diego. "Since last you wrote," he says, "I've attempted to compare the Foucault test with the Ronchi, on several surfaces, both directly and with a flat. Briefly, my conclusions are:

"1: The two methods are equa1 in sensitivity at f/6 direct, and at f/12 with a flat.

"2: Ronchi is better at large aperture ratios: f/l, f/2.3, f/4.5.

"3: Foucault is better at small ratios: f/6.8, f/8, f/10.

"4: Neither is sensitive enough (0.1 wave) below f/4.5.

"5: Straight-edge, diffraction (Everest test) and Ronchi are equal for edge.

"6: When using a flat or a Hindle sphere, these surfaces must be pretty near to fairly good: 0.1 wave is none too close.

"All of the above was done with 120-line- per-inch Lower wire grating and smoked razor blade. In all comparisons, source (pinhole) and eye were precisely together on the axis. Surfaces used had apertures of 1.09, 1.4, 2.3, 3.5, 4.5, 6, 8, 10 and 11.3. Sensitivity was judged by polishing grooves in surfaces with pitch laps l/8" diameter, loaded 50 grams per square centimeter, and using black rouge washed from worn-down stock.

"Don't forget," Selby adds, "that other may not get the same results."

Comments on the above: Everest-"I choose the old tin can and razor blade." Sheib- "Interesting. I agree with Selby on No. 3, also No. 4 and No. 5. I am not sure I agree with him on No. 1 or No. 2."

Well, there it is-now it is a public fight along with who is going to be the next president. Great pains should be taken t eliminate variables, in making tests similar to these.

HERE are some further data from Selby who is the one who made the "dinosaur" telescope described last July, also whole fleet of flats.

"Regarding the cutting speeds of polishing materials," he says, "I find:

"With very hard pitch, No. 600 pits, load 50 grams per sq. cm., stroke 250" per min:

"Very hard laps of pure pitch polish much slower than pure pitch laps of medium hardness on Pyrex.

"Regarding tendency to scratch, with superhard laps on Pyrex, B. and L. sleeks and scratches least, Clark next, then Fuller's black, then Am. Opt. Co., and worst, H. W. and M.; although, with a medium lap, none scratches at all."

Naturally, this is only one man's findings. He does not claim they are final.

In Selby's notes, "Black Arg. Glass" refers to a special melt called "Marbletex," from Wells Glass Co., Kokomo, Ind. "H. W. and M." refers to Hanson, van Winkle and Munning Co., East Matawan, N. J. "Clark" refers to Alvan Clark and Sons Co., '' Somerville, Mass. The other two are mentioned in "A. T. M." The black "rouge" was from W. P. Fuller Co., San Diego, Calif. Binney and Smith, 41 East 42 St., New York, make black rouge but your scribe has not yet tested it. Some black "rouge" which H. A. Lower sent him proved to be as scratchless as a newly hatched chick. It is slow (note Selby's figures), but after no end of trouble with scratches Lower found it a haven of rest.

THE cut at left shows how W. B. Hiner, 123 Cleaves Ave., San Jose, Calif., added a Barlow lens to an eyepiece. In this case it was one component of an old camera lens, a meniscus. The Barlow principle is explained by Hindle, in "A. T. M.," p. 215. If the lens is arranged to slide along the axis, as explained in "Splendour of the Heavens," p. 751, the amount of magnification may be varied at will.

A NEW aluminum evaporating outfit installed by Leroy M. E. Clausing of Chicago is shown opposite. He writes: "The enclosed print is one that I made of the evaporating outfit. The streaks of super brilliancy on the 20" flat are not caused by super-reflection, but are due to my moving the light to the wrong place while taking the picture.

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