MOSQUITOES IN SUMMER, and cold in winter. Most amateur astronomers put up with these troubles in observing because the construction of a warmed observatory room, such as those described by Porter and others in "A.T.M.," is relatively formidable. One such type is the turret telescope and of these there are now about half a dozen. One of them, warmed electrically, has just been constructed by Roelof Weertman, of Dutch descent, member of The Amateur Astronomers Association of Pittsburgh, residing at Division Lane. Observatory Hill, Vanport, Pa., 25 miles north-west of Pittsburgh (mailing address, R.F.D. 1, Beaver, Pa.), and is shown in Figures 1, 2, 3, and 4. This is a larger, heavier more elaborate installation than the illustrations at first suggest, the parts above the roof-line alone weighing 1500 pounds.

The telescope itself, when examined closely, proves to be more conventional in type than the first glance suggests. It is a simple, ordinary Newtonian, 12 1/2" in aperture, an f/9; its 100-pound counterweight being carried on an extension of the tube rather than in separate form. This makes the tube 14' long. There are no added reflections-no siderostat as, for example, at Stellafane's turret telescope. This, of course, entails reversing the dome-toward the building as shown.

In this type of telescope the observer within the dome looks into an eyepiece which lies in the declination axis. He also stands within the polar axis, which is expanded into a big ring to permit his entrance into it.

Starting at the bottom and working upward, as in the actual construction, we have in this telescope the following catalog of elements:

A reinforced concrete foundation on bed rock.

A hollow tile building of dimensions shown in Figure 4-narrow enough (56") to permit the tube to reach the zenith on either side.

A 2" plank floor and a 2" plank roof deck, the latter covered with tinned iron and painted.

Inside the building a stairway, as shown (Figure 4). This is only 24" wide and is on the side nearer the reader. At its head is a trap door 24" wide, and beyond this a fixed section of platform also 24" wide. The entering observer

pushes up the trap-door, climbs up on the fixed platform, lets the trap-door down, and thus is on a platform 33" wide and 48" long. There is ample room for two observers, but three's a crowd. Well, sometimes.

Surrounding the rectangular opening through the roof deck, where the dome emerges, a large, rectangular, horizontal iron base, 51" by 33".

Welded to this, four upright struts of 2" pipe, to carry the tilted ring.

Fixedly welded to these four supports, a 315-pound ring of 50" inside diameter, made of 3 5/8" by 4 3/8" angle

iron, and slanted at 49°15'. The web space between the basal rectangle and the fixed ring is filled in with metal lath and plastered inside and outside with 2" of concrete through which there is a window (Figure 2) 14" by 27".

Bolted to the fixed ring, three 3 1/8" ball-bearing rollers from automobile rear axle housings.

Pressed on one of these three rollers a 10" worm wheel to provide the friction drive to rotate the dome (done by an automobile window crank).

At right angles to these rollers, two 4 3/8" thrust bearing rollers to prevent the movable ring and its attached telescope from slipping off.

A 215-pound movable ring of 3 5/8" by 4 3/8" angle iron. This carries the telescope, the dome, and the hour circle.

Welded on the movable ring a 2' length of 4" by 6" angle iron, as a base, and on this a square piece of 12" flange beam, stood on end. This unit carries the mounting for the tube, also a declination slip plate, eyepiece holder, holder for 2 1/2" elliptical flat, declination and setting circle, declination worm, and ball bearings. A blueprint of these details may be had gratis from the owner.

In its swing, or traverse, the eyepiece does not rise more than 1' above its lowest ( E. and W. ) positions.

On the above unit the tube, 14" inside diameter, built of 1" by 1" tee-bar straights and 1 l/4" by l/4" by 1/2" hoops.

At its upper end the tube carries a 100-pound counterweight.

Attached to the movable ring a dome of galvanized, riveted, sheet steel. Its interior is marked with latitude and meridian circles. Prominent stars and nebulae are indicated on it, with their R.A. and Dec., so that these and other landmarks can be found instantly.

A 12 1/2" mirror which, before silvering, was subjected to the criticism of Norbert J. Schell, Beaver Falls, Pa., of off-axis and criss-cross off-axis telescope fame.

When the telescope is not in actual use, the mirror is left in it covered by a latched lid. A 3' sack, like a big mailsack (Figure 3), is drawn over the end of the tube as a protection against rain, and the tube is then turned mirror end up.

The 300-pound tube unit, including the tube's own 100-pound counterweight, is hung on one side of the movable ring. This is balanced by a 570-pound counterweight mounted inside the dome opposite the telescope.

In the photographs (Figures 1, 2, and 3) are seen respectively: Weertman; Billy Weertman, Mrs. Weertman; John Cool, Billy again, and at ground level Mrs. Weertman again with Betty Tulip Weertman, Billy's goat (not, however, a billygoat). All-especially Mrs. Weertman-assisted in the work, even Betty. That is, when anybody made a mistake, Betty was the goat.

Weertman says the observatory once served as a fort. No sooner had he finished the concrete doorstep than a "halitosis kitty" ambled up, drove him inside and left his or her footprints in the soft concrete.

Altogether, this is a notable telescope.

PARTIAL silvering, sometimes spoken of as half-silvering, is sometimes desired for optical instruments. Accomplishing it by the familiar Brashear process often requires agility and involves an element of uncertainty, since the silver ordinarily is deposited too quickly to permit calm, steady observation and quantitative control. Two readers of this department, Dr. Henry Paul, of the Norwich Pharmical Company, a chemist, and Dr. Wilbur Silvertooth, of Paramount Pictures, Inc., a physicist-both amateur telescope makers-have called to our attention a new method of partial silvering originally described in Industrial and Engineering Chemistry (May, 1942) by Robert D. Barnard, M.D., of The Chicago Medical School, as follows:

"The surface should be cleaned with hot chromate sulfuric acid solution and thoroughly rinsed with distilled water. It is unnecessary to use the application of caustic soda so often recommended. If a drop of distilled water will spread evenly over the entire surface, it may be considered free from grease or other organic matter.

"About a half liter of (1) a 10 percent silver nitrate solution containing one or two drops of concentrated nitric acid and of (2) a 10 percent solution of technical triethanolamine are conveniently made up. Both solutions will keep indefinitely.

"The surface to be mirrored is placed face upward in a clean Petri dish of sufficient diameter to accommodate it. To 25 cc. of solution l in a large test tube are added 10 cc. of solution 2: then, with constant agitation, further additions are made of 2 or 3 cc. at a time just to the point where the precipitate which forms on the first addition clears completely. The mixed solution is poured immediately over the object to bc plated so as to cover it by a layer of at least 0.25 inch. The deposition of silver begins within a few seconds.

"For the half-reflecting surface required for interferometers, a layer of silver which transmits about as much light as it reflects is ideal. Such a layer has a distinct violet tinge and appears within l0 minutes at room temperature.

"For completely reflecting surfaces, the immersion may last for 24 hours; this particular bath is unique in that the deposition seems to be continuous for that length of time.

"The Petri dish gives good visual control of the extent of plating, since deposition of silver occurs only on a surface and not through the body of the solution. It is possible that the low surface tension of the triethanolamine may be responsible for this phenomenon.

"When the desired thickness is deposited, the plated object is taken from the bath only the edges being handled."

Dr. Silvertooth, mentioned above, states that "We have used the method here at Paramount Pictures, Inc., with considerable success, in preparing partial transmission films."

Dr. Paul, also mentioned above, suggests caution in adding nitric acid to as concentrated a solution of silver nitrate as is used in the Barnard Method-risk of explosion (see warnings in "A.T.M.," pages 412-415). In this, Dr. Barnard concurs.

The triethanolamine needed is easily obtained through chemical supply houses.

Replying to a private communication, Dr. Barnard emphasizes again that his method was devised particularly for partial transmitting surfaces, and points out that, for full reflecting surfaces which require a heavier coating, the original triethanolamine method developed by Professor M. Meltsner, of the College of the City of New York, described in U. S. Patent No. 1,988,764, is more suitable. "Difficulties will arise in the latter case," he writes, "and the directions in the present article will have to be modified by using a much higher concentration of triethanolamine, even up to a concentration of 90 percent. Because of the difficulties encountered with the variation in composition of commercial triethanolamine solution now available, the method used in the cold. as I described it, requires a certain amount of manipulation for best results. Samples of triethanolamine containing a large amount of volatile alkyl amines (strong fishy odor) should be rejected, as should those with a large amount of chloride present. These do not appear to interfere with the Meltsner Method as much, though the last method is inapplicable to surfaces which cannot be heated."

DRIVE, clean. simple, free from gadgets and hickerpickers. made by N. J. Schell, 1019 Third Avenue, Beaver Falls, Pa., is shown in Figure 5. Asked to describe it, Schell writes:

"The drive is used with an equatorial which has for its upper polar bearing a large cast iron flange, or plate, which rolls on two ball-bearing rollers (Porter's design, I believe). I found it would be necessary to re-build the whole thing if a worm-wheel was to he used, so tried using a thin band or belt of phosphor-bronze (continuous) which passes around both rollers and under the large flange. This hand is just taut when the weight is on it.

"The hand is pulled by a screw of 12 threads per inch, by means of a nut which has a yoke over the top-the band passing between the top of the nut and the yoke. An eccentric pin or shaft enables the band to be clamped firmly to the nut at any point, a simple wrench turning the eccentric pin as shown. When not clamped, the band can slide freely as the mounting is moved in right ascension.

"The drive begins with a 12-watt Telechron motor which is enclosed in a box below the main plate, continues through a train of helical gears in the narrow box at the right, terminating in the screw. The knobbed wheel on the gear box is a clutch to disengage the gears, which is necessary in order to run the nut back on the screw after it has traveled from left to right. This takes only a minute or so and, as it takes about three hours for the nut to travel the length of the screw, a single resetting will take care of an entire evening.

"The whole assembly, with the exception of the band, is in one piece and is attached by the single bolt shown just below the wrench (the pin and yoke are first slipped off, however, and the band remains on the mounting). The base of the assembly is 1/2" steel plate. The bar below and parallel to the screw serves the dual purpose of tie-rod and guide for the nut.

"There is no claim for originality in this design."

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