THIS month, instead of the usual description of telescopes made by the amateur from the instructions in the SCIENTIFIC AMERICAN book Amateur Telescope Making," we present a few "accessories" and some odds and ends of the art. One amateur who seems to be everlastingly at it is Harold A. Lower of San Diego California (1032 Pennsylvania Avenue). We have published photographs sent by Lower on one or two previous occasions and now we show one of his water-clock drive; also one of a flat he has made. Lower writes: "The picture shows about all there is of the clepsydra or water-clock. Everything is made of brass except the piston, which is aluminum. The inside of the brass cylinder was highly polished and the piston very closely fitted. There is so little friction that the piston will move of its own weight. The cylinder is mounted horizontally so that the changing weight of water will not affect the rate. The apparatus works much better than we expected. No tremors due to the drive can be detected, even with a high power eyepiece. The motion is smooth and steady."

The principle of the clepsydra is simply water escaping through a minute opening. This allows a piston gradually to move and the piston rod actuates the telescope tube through some mechanical connection; in the present case by a length of picture wire. It is said that one must be fussy with details in order to make one of these things work accurately and smoothly. In fact, that is just what we had advised Lower before he made it, but it didn't stop him and he "proved the pudding." Later he sent us a word of warning based on the experience he gained: "First," he says "there should be a screen to prevent dirt in the water from getting into the needle valve which lets the water out. Secondly, the needle valve requires a fine control; an old radio vernier dial works fine." The cylinder is usually placed on the north but Mr. Lower moved it to the east side, as shown, in order to photograph it.

Lower sends in a detailed criticismof his own flat; it is only a maiden effort, he says. The edge is turned (they usually are) but he expected that and purposely began with a larger disk (12 inches) than the flat he needed. Just inside the edge there is a raised zone of half a fringe (less than 1/200,000 of an inch). The irregularities near the center will be in the shadow of the secondary used in testing a Cassegrainian. The photograph was taken by blue light, hence the inaccuracies show up more than yellow sodium light, with its greater wavelength, would reveal. The photograph does not do the flat full justice.

OPPOSITE is an observatory by G. F. Hofferberth (Rural Route 13, Day. ton, Ohio). Hofferberth was one of the earliest telescope makers. He says: "Boy that curved dome was some job [told you so]. Every time I wanted to add a piece of roofing it had to be cut curved, but the dome sure is a daisy. The dome framing is of wood and the shingles of Compo pitched down with steep roof pitch. The dome is 6 inches in diameter." Hofferberth, in an unguarded moment, has confessed that he built the dome in a barn and then had to tear off the side of the barn in order to get the dome out.

FROM Pittsburgh comes the following, signed by Leo J. Scanlon, Sec.-Treas. of the Astronomical Section of the Academy of Science and Art of Pittsburgh (1405 East Street, N. S. Pittsburgh Pa.). "Here is a brainstorm I had recently for getting the most out of a prism or flat, when it is desired to use a finder on a telescope. When a prism is used you simply silver the back of it and use the silver surface for a flat mirror in the optical train of the finder; when a flat is used you silver both surfaces of the flat" See Scanlon's sketch.

BELOW is another which is no more of a "brainstorm" than the first-on the contrary, pretty good, we think. The writer is E. Lloyd McCarthy of Canton, New York (10 Powers Street). "In brief," he says, "the idea is to use one eyepiece for the finder and speculum also. When the slide carrying the small 45 degree mirror is pulled out the mirror delivers light from the finder to the eyepiece. When the object is in the center of the field the slide is pushed in allowing the light from the speculum to pass through a hole in the slide and thence to the same eyepiece." Can you beat it?

IT appears that each and every amateur worker must have obtained a copy of the Bureau of Standards' Letter-circular 32, on Silvering, as the Bureau has repeatedly been forced to prepare new editions. This rough, mimeographed publication has now been replaced by Circular 389 of the Bureau, entitled "The Making of Mirror by the Deposition of Metal on Glass." This is a printed pamphlet and a valuable source of practical information. It is no longer to be obtained from the Bureau but from the Superintendent of Documents Government Printing Office, Washington D. C., the price being five cents and, by the way, the Government will not accept payment in postage stamps.

In this new circular on silvering the Bureau, at which quite a lot of silvering is regularly done, lays new stress on the risk involved in silvering by the Brashear process. One is taking an entirely unnecessary risk, they state, "probably greater than is commonly realized," in silvering without goggles. We never have received word of a single explosion due to silvering, though several thousand have silvered. Can any one tell us of a concrete instance? On general principles it is, of course, better to b careful than sorry and we have no motive for minimizing the risk or pooh-poohing it.

The same circular states that the reducing solution does not deteriorate with age. This statement has appeared many times and probably is correct. On the other hand we recall seeing in one or perhaps several rather recent periodicals or books the statement that reducing solution improve with age, up to a certain period, and then a deterioration sets in. Can anyone advise us where such statements have appeared? We have lost the reference.Apparently the Bureau has upset the claim that the Brashear process of silvering gives a coat that reflects more light than the others. However, as our space is used up, let the worker obtain the circular and read about it.

The Society for Amateur Scientists (SAS) is a nonprofit research and educational organization dedicated to helping people enrich their lives by following their passion to take part in scientific adventures of all kinds.