"The second is an f/6-1/4 unity-amplification telescope-primary, 75" focus, 5" secondary is a plane mirror 43-3/4" from the primary. The secondary focus is 12-1/2" in front of the primary.

"The third is an f/2 Schwartzschild telescope-primary 60" focus. The 6" secondary is 30" from primary, and has a radius of curvature of 40". The secondary focus is 12" from the secondary, which is concave.

"The above figures," Mr. Kirkham states. "accept a 12-inch telescope as being the smallest size (possibly ) to which R-C or Schwartzschild curves may advantageously be applied. A ten-inch could be made by adhering to specifications, but disregarding the 6-inch zone "

IN the Astrophysical Journal for May the astronomer Frank E. Ross of Yerkes describes experiments which have recently been made with a correcting lens inserted in the reflected cone of rays. Its purpose is also to eliminate coma. He prefers this form of correction to the aplanatic types of mirrors. This type of lens has been tried on the 100-inch, the 60-inch, the 40-inch refractor and 24-inch reflector at Yerkes, also on10-inch and 3-inch telescopes. The correcting lens for the 60-inch is 8 inches in aperture and is placed 15 inches from the Newtonian focus. In two illustrations below, reproduced from the Astrophysical Journal, the star images were taken about half a degree off the axis, one without the Ross lens, the other with it. Judging from what has appeared in print and what has been said, the Ross correcting lens is not a suitable job for the tyro. This is putting it mildly.

A PLANATIC telescope designer Kirkham, previous to starting an aplanatic recently completed a stubby Cassegrainian similar in appearance to the one show on page 451 of "Amateur Telescope Making." "Attached," he writes, "is a pair of photos of my latest, and here's the dirt: Six-inch primary is of 15-3/4" focus. Secondary is 2" diameter and the e.f.l. of the combination is f/10. It works like any Newt, and has a wide clear field in daytime. One can read signs and billboards five miles away, even with a 1/3" ocular, which magnifies about 200 times. The tube is spring brass, chrome plated. Fork, cell and so on, are cast aluminum-everything else brass. The rig weighs about 12 pounds, including tripod. Star images are tiny dots of light, and the diffraction rings are according to Hoyle.

"Coming back to focal lengths of f/20. f/40 and above." he continues, "that's what's given us the crack about a Cass not being as good as a Newt. One goes to investigate a complaint about Cass and Greg and finds that the eager fellow has tried to make a perfectly good Newt into a Cass simply by making a secondary. The result is f/35 or f/40 and no one can get away with that. There's no reason for making a Cass longer in focus than one would a Newt. One must therefore cut the primary to f/3 or f/4 and design the secondary to give right results with f/8 or thereabouts.

"Why, then bother to make a Cass at all ? Here's why. The thing is short and stubby and easily mounted, convenient to use; also, since there are two curves, they can he made aplanatic."

HERE are two amusing sidelights from the earthquake zone-rather late, but these columns have been filled recently with other matter. Dr. C. N. Lord, dentist, 520 Temple Avenue. Long Beach, California, was photographing the moon with his 8-inch reflector and a Brownie camera when the quake hit. The photograph obtained looks decidedly shimmery (too much so to reproduce). This, so far as we know, is the first practical application of an amateur's telescope as a seismoscope. Everything fell about the telescope but did not hit it, and Astronomer Lord heroically stuck to his post. The other incident was reported by Mr. Ferdinand Ellerman of Mt. Wilson Observatory, who wrote: "I had just silvered the 100 inch mirror and had gotten the finest coat ever put on it. While we were at dinner the earthquake occurred, jarred the telescope enough to spill some mercury from the float down on to the mirror and ruined the silver coat." Russell W Porter describes the same incident at greater length: "Humiston, the astronomer, came down off the mountain today with the strangest tale of what the earthquake did to the 100-inch telescope mirror. It seems that the mirror was resilvered only yesterday. This is done twice a year. It has be removed from its tube and lowered through a manhole in the floor, into the silvering room. Well, Humiston said they put on a beautiful new coat of silver and went to supper. At the first shake they all hurried to the big telescope, to find to their consternation that the new silver coat had disappeared. This is what actually happened: The telescope mounting, weighing some 50 tons, has its polar bearings floating in mercury. The mercury had been forced out of the containers, pouring across the floor to the manhole, and down on the mirror. They are resilvering it again today."

WHEN doesn't a totally reflecting prism totally reflect? When the hypothenuse face is silvered, as occurs in combining the diagonal for a finder with the outer hypothenuse face of the main prism. Experiments described in the Revue d'Optique, October, 1932, show that a coat of silver on the outside, especially if thick, actually affects the percentage of inside reflection as much as one half. To test whether the reflection had really been changed to metallic reflection, mercury was placed against the outside, instead of silver. The index of reflectivity was then the same as that of mercury, showing that the reflection was metallic. Just why this change takes place is not stated. Maybe nobody knows.

"THE Bulletin" is the name of a monthly publication of high intrinsic merit sent out by "The Texas Observers" 312 West Leuda, Fort Worth, Texas. Its emphasis is on observing and it is well worth the dollar a year it costs.

As is now well-known, a 76-inch telescope is soon to be built for the University of Toronto. We learn that its mirror disk is to be of Pyrex and is shortly to be shipped from the Corning Glass Works at Corning, New York, to Sir Howard Grubb. Parsons and Company, at Newcastle-on-Tyne, England, for figuring and mounting.

Can anyone furnish the specifications for designing a telescope rifle sight? We receive occasional requests for these data but have not been able to lay hands on any kind of working specifications.

Here's a note from "Wally" Everest, the HCF man, who lives at 15 Allengate Avenue, Pittsfield, Massachusetts, in which city one of the big General Electric shops and laboratories is located. He says: "Things are moving fast up here. We are forming 'The Berkshire Astronomical Association' which will include some of the best brains in the local branch of the G.E. Co. -about 40 men of more or less important standing here. About15 are making telescopes. As many more are rarin' to go and the rest are interested in the mathematical or scientific side of it. It's getting terrible -the whole gang is simply going nuts possibly finding in this game a welcome relief from the mental strain of the depression. You can any time see a couple of birds, high up in the organization, discussing some fool point in connection with astronomy or telescope making."

If the depression has been driving you crazy, don't consult a psychiatrist. Instead take up the hobby of telescope making and stay crazy about something really worth being crazy about. There are now several thousands of us, some of US harmless, who are crazy over this lobby. Investigate.

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.