"The mounting is of the Everest 'Town Pump' type, described in Scientific American, May 1930. I saw the 'Town Pump' when it was shown at Stellafane, and copied a good many features of it, although mine starts with a rear axle differential carrier for a polar axis. This automobile part is ideal for the purpose, as it has two axes at right angles and the declination axis can be large. Only a few makes of cars have suitable carriers, as most of them have oval or square rims, and some have the pinion shaft out of center with respect to the rim. I wonder that this auto part hasn't cropped up before as a mounting, but I know of only one other-Leuchinger's. [A. R. Leuchinger, Wantagh, N. Y.-Ed.] The old Chevrolet carriers are dandies for the purpose and can be had in any auto graveyard. This Chevrolet carrier is riveted to a torque tube, and Porter could make an elegant mounting design by running this tube through bearings in a concrete pier and dispensing with the rollers under the rim. This would make a simple mounting for those who are not equipped to do considerable machine work.

"The telescope, a 6", has an octagonal tube of wood, 7/16" thick, which rotates in rings made of brass channels rolled circular. It has a phonograph motor drive [This part will be described in the 'A. T. M. Supplement,'-or 'A. T. M.,' Vol. II, as it may now be called-some time later.-Ed.] No vibration from the motor is apparent, even when using a magnification of 425 diameters, and the motor can be wound without disturbing the field of view of a 1/2" eyepiece. I paid a dollar for the differential carrier and, excepting eyepiece and finder, the whole telescope cost about 25 dollars. In general, the mounting is about the same size as Everest's, with still larger bottleneck. The declination axis could be shortened 2 or 3 inches to make it more compact. The counterweight rod slides into the hollow declination axis."

McCartney concludes, "Yours for bigger and better bottlenecks," and he is right-we are for them. So let's hope that more "Town Pump" and "Hempstead Hydrant" mountings will be created, in the interests of solidity.

While McCartney's bottleneck with 3" diameter, isn't quite so chunky as the real bullneck shown in Porter's drawing in "A T. M.," few are equipped to go literally quite that far, though it would be desirable. Someone thought Porter's other sketch- the right hand one in Figure 2, page 131, "A. T. M.,"-was perhaps a caricature and a bit skinnier than any that have actually been made, so we reproduce a photograph of one that is mounted on real "pipe stems" of the kind that Ellison in a letter we published some time ago, called "whippy."

ANOTHER solid mounting of the "Town Pump" type is shown on the opposite page. E. R. Richardson, San Gabriel, California, is the maker and the telescope is a 12-1/2" Pyrex (looks as if this one were almost the thirteenth member of the "Twelve Inch Club,"-but it turned up after that page had already been made up). "This mounting is built around a 14", 120-pound fly wheel which I salvaged from the scrap pile of a local foundry," the owner writes. "The axes are from an auto wrecking yard-truck rear axles 2" diameter and of finest steel, and the rollers are truck ball bearings with double rows of balls. The moving parts weigh over 400 pounds, yet there is very little friction and a 1/25 H.P. synchronous motor drives it."

It begins to look as though Porter's heavy emphasis on mass in the design of telescope mountings were bearing fruit.

In his most recent letter Ellison again reverts to "whippy" mountings-the term, an apt one, was in an earlier letter of his which was published here: "Just a remark on whippy mounts and slide-off observatories. The run-off roof-or run-off shed-is doubtless the easiest to construct. But when you come to work with it, you may well regret that you took the easiest way. The advantages of the revolving roof are that it keeps off (a) wind, and (b) radiation. Even the most rigid mount will vibrate in a breeze, and as for a whippy one, the images execute such a war dance that observation is hopeless. And, if your telescope tube is of sheet metal, as it is three times out of four, you will find the images play the most extraordinary pranks. Often they are like hairy caterpillars. On a clear night, especially if windless, the upper side of the tube gets cooled by radiation, probably several degrees below the lower, and the upper half of the mirror gets cooled below the lower half. Well anyone who knows mirrors and their little ways can tell you what that will mean. The remedy is either a wooden tube, or a roof over the instrument. No amount of swathing in felt and so on, will mend matters."

From this subject Ellison shifts to bees wax, and gives us the history of its recommendation in his treatise in "A.T.M.," along with the "Swedish pitch" ("A.T.M.," p. 75) which no Yankee has ever been able to find; telling how, in his own mirror making, the two of them have now given way to coal tar pitch as is also happening in the U.S.A.

"About that coal tar pitch. The whole trouble began with the old masters of the art in the seventies and eighties of the last century. These old fellows, like all their Victorian generation, were saturated in pedantry, and gave whole pages of directions which I gradually found to be so much 'bunkum,' and scrapped bit by bit. One of these directions was that the pitch must be only the best, and the best meant Swedish pitch. Now Swedish pitch is vile stuff, is full of dirt, and has to be strained; also is desperately sticky. It was in trying to devise some way of mitigating its stickiness that I adopted the plan of mixing in a percentage of beeswax.

"But one time I was in a benighted place where Swedish pitch could not be obtained, and had to put up with what I could get, which was coal tar pitch. And, to my surprise, the stuff figured far better and more certainly than the Swedish. I sometimes mix resin with it. That is good stuff too, but needs a lot of softening with turps."

Ellison then comments on the HCF lap: "I gave the HCF dodge a good try-out, and I find as Everest does. It is unnecessarily complicated for figuring, but for quick polishing it is the goods. I merely pour the hot pitch on the glass tool as usual, but immediately lay a sheet of HCF on it, and press the mirror on, previously covered with a paint of rouge and water. [See A.T.M., p. 367.-Ed.] The heat of the pitch softens the HCF, and it takes the curve very completely. The sheet of HCF need not be the full size of the tool, as it flows under pressure, and spreads to 25 percent or more wider than it was. After this I cut out facets just as usual, only the HCF plus pitch is far easier to cut than plain pitch. This too is fine for polishing. When it comes to parabolizing I make an ordinary tool of the coal tar stuff."

Never having observed HCF flow or spread under pressure Ellison's mention of a 25 percent spread causes one to wonder whether Irish HCF and the Yank variety are quite the same thing. They might differ.

Ellison next comments on the rubber "Door Mat" for tired lap makers: "The very latest stunt seems to be casting the tool by means of a rubber honeycomb mat made expressly for the purpose. I have no doubt that it will work, also that it will be a godsend to many. But I can tell you a story of the same idea, which I tried out in 1890, in collaboration with a friend and former pupil, Dr. Nathaniel H. Alcock, one time Professor of Physiology in McGill University, Montreal. We made a sort of honey- comb mould by cutting out 1" squares in a sheet of plywood. The cutting was done with a fret saw, and the thing when finished ~u was just like the rubber mold, except that it was not pliable. The squares were smoothed with a sharp knife to an angle of 45 degrees inside, and the whole thing dipped in water, and laid on a wet surface. The pitch was ladled into the squares with a teaspoon and when hard was pushed out, and each facet cemented to the face of the glass tool by holding the back of the pitch square to a flame for an instant. When all the squares were in place the tool was held in a basin of hot water till soft, and the facets moulded into contact, by pressing the mirror on in the usual way. The method had the advantage that, if any facet were damaged or detached, it was easy to make and attach a new one. I soon got tired of the tedious job, and found my own way, did all that was required, and did it in far shorter time."

This resembles the method described a little later by Ritchey. Everest no longer spoons the pitch into the "Door Mat," but pours a regulation lap and then pushes the "Door Mat" down into it by means of the mirror, using plenty of warm soap-suds.

MAKING his own drawings, which are reproduced here, Raymond A. Sholes. 10004 Regent St., Los Angeles, California, describes a bit of his technique, as follows:

"In the February number, Nicholas M. Smith's method of testing was described; also Ellsworth L. Martinelli's technique for using HCF. The success of both depends upon knowing the diameter, or radius of zones, which must be measured while the eye is at the knife-edge. Both Everest's and Mason's methods of measuring are O.K., but I hit upon the idea shown in Figure 1 of the accompanying drawing, which has the advantage that it allows the operator to view the whole mirror and yet measure any zone as accurately as is necessary.

"A piece of stiff cardboard was marked off in l" squares, and a hole cut in it, somewhat larger than the mirror, the center of the hole being located where two of the lines cross. Silk threads were strung across the opening both ways, located on the pencil marks. The card was tacked to a block of wood and stood in front of the mirror, as shown, while testing. It must be so located that the center cross is directly in line with the center of the mirror. The threads make black lines where the mirror is light and bright lines over the dark areas. These do not interfere with viewing the shadows as shadows, but are always there to refer to when wanted.

"The crests can he measured and checked both on the vertical centerline where the shadows reverse and on the horizontal centerline where one would normally place a mask. Checking one against the other leads to greater accuracy, For a large mirror, the cardboard would have to be replaced by a piece of plywood or a wooden frame.

"While using underlays and HCF, as described by Mr. Martinelli, my experience was that the work done on the glass is always a little toward the center from the underlay. A typical set-up is shown in the upper part of Figure 2. The lower part shows the result-a depressed zone just inside the raised zone that was being attacked. I found that if the inner diameter of the underlay is made the same as the highest part of the zone, and the outer diameter a little larger than the zone diameter, as shown in Figure 3, there was no tendency to create new zones. Even when a raised zone was near the edge the underlay, as shown in Figure 4, brought it down-believe it or not-without causing a turned down edge."

STELLAFANE convention this year, Saturday, August 8. Porter probably coming.

WE learn that the 4-3/4" x 6-1/2" Saint-Gobain low-expansion glass flat, also the machine, with which Ritchey made the 40" Ritchey-Chrètien a year or so ago, are lying idle in Washington. If some amateur club would pick up these items an interesting club project of some sort might be worked out.

IF you feel you need more materials in

order to swing the telescope making hobby, listen to this, from Bre'r Fred Ferson of Biloxi, Mississippi-just one of the TNs. "I am going to, start the Ferson Plan for the redistribution of telescope materials, and call it 'The Share the Wealth of Telescope Materials'. Every man who joins by paying Ingalls and Ferson six bits might receive one brick building, 20' x 100' with tower and dome, one large and one small lathe, a milling machine, drill press, shaper, planer, a forge, optical spindle, grinding machine and motor, and small tools and sundries too numerous to mention. Also one Pyrex disk, and tool per month-prism blanks, rouge, pitch and 'Door Mat'. Last but not least, $200 per month per TN."

To this great plan for spending our way into vast wealth Ingalls adds a compromise arrangement by which the work is to he divided between Ferson and himself. Ferson is to provide the materials and Ingalls will get the six bit dues. All of the benefactors must agree to drop and break the mirrors before the last day of each month, thus adding to the wealth of the community by making the remainder of its members work that much harder, as well as "putting money into circulation." Local organizers' salaries will be limited to nominal sums-say $12,000.

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