The first concerns a telescope made by a Benedictine nun, Sister Cornelia of Mount Saint Mary's Convent in Pittsburgh, whose photograph, kindly sent us at our request by her mentor in telescope making, Leo J. Scanlon of that city, is reproduced above. Sister Cornelia is an instructor in mathematics and physics at the high school in the Convent. "Before the bell sounds at 4:30 in the morning, summoning the nuns to chapel," says the Pittsburgh Press, whose photographer took this photograph, "Sister Cornelia trains her lens from her window to see Venus." The amateur telescope makers of Pittsburgh have elected Sister Cornelia an honorary member of their organization.

THE second picture shows the 120-inch Pyrex disk arriving at the optical shop of the California Institute of Technology. This disk is being figured as a flat for testing the 200-inch disk. The larger 200-inch disk cast last March at Corning was pre-cooled rapidly from 1800 to 120 degrees Fahrenheit, to permit an examination, which showed it to be crystal clear, free from cracks and bubbles. Whether the same disk will be repaired, annealed and used, or a new one cast has not been decided at present writing (July 20), newspaper reports to the contrary notwithstanding.

The 200-inch mirror is to be aluminized, not silvered, and no doubt, when the time comes, that job will devolve on Dr. John Strong of the California Institute of Technology, the man who has mainly developed this process. In the meantime Dr. Strong keeps his hand in by aluminizing various smaller mirrors from the 30-inch Crossley reflector at Lick to a three-inch mirror he gave to your scribe. A snapshot of Dr. Strong, taken by the same humble scribe, is reproduced on this page. An eight-page article by Dr. Strong, on evaporated aluminum mirrors, appeared in the February 1934 number of the Publications of the Astronomical Society of the Pacific. This article gives the best data thus far made available on this work.

SIX or eight years ago a very young lad named Evans besought our aid in building a telescope, and now his endeavors have finally led him to choose astronomy as a profession. Accordingly he has specialized in that science when in college, and has become just what he set out to be. Mr. Evans (see photograph, opposite page) did his undergraduate work at Swarthmore and has been an observer in the Flower Observatory of the University of Pennsylvania and a graduate student in astronomy for the past year or so. Next year he is to be at the Oak Ridge Station of the Harvard Observatory, with his principal duty as assistant to Dr. W. A. Calder in photo-electric photometry with the 61-inch reflector. Here is one amateur telescope maker who has already lost his amateur status-gone professional. Dr. Calder is another victim of A.T.M. who switched over from physics after making a telescope.

A DRAWING on the opposite page shows the mounting for the new 32-inch reflector at the Provence station of the Paris Observatory, as described in the Journal of the British Astronomical Association (Vol. 44, No. 5) by A. F. Bennett, F.R.A.S., who points out that in this design all esthetic considerations have been subordinated to simplicity and absolute rigidity. The polar axis is set definitely out of center to diminish the unbalanced effect of the tube. The leverage of the tube around the axis is thus reduced, while at the same time the heaviest part of the axis serves as a large part of the counterweight. The mounting is a combined Newt-Cass, and the diagonal is oddly set in order to reflect the rays out at a 125-degree angle. The 32-inch mirror is only 3 inches thick and, but for the lever supports, its flexures, which figure out 50 times the allowable limit, would be bad. Other things being equal, the deformations of mirrors due to their own weight, Mr. Bennett points out, are in the ratio of the fourth power of the diameter divided by the square of the thickness. An interesting piece of engineering design.

SOME workers take zone radius readings on mirrors by means of micrometers attached to the knife-edge, and express these in thousandths of an inch, which implies a high degree of accuracy. However, the question has arisen whether readings finer than hundredths of an inch do not represent fictitious accuracy. The worker may set the micrometer, and he may make the readings in thousandths of an inch, but can the eye estimate the opposite zones under comparison closely enough to justify these very precise readings? The ability of the eye to do this-its "contrast sensitivity" -varies with the amount of illumination (see, for example, Hardy and Perrin, "Principles of Optics," under "Fechner's fraction"); also with the distance of separation of the illuminated areas.

We submitted this question, with a sketch of the typical Foucault test set-up, to a noted physicist-illuminating engineer, and he answered as follows:

"You bring up the question of the photometric accuracy. This largely depends upon a perfect juxtaposition of the two brightnesses being compared. Under these conditions brightnesses can be compared to an accuracy of a fraction of a percent, providing a number of readings are averaged. However, ordinary photometric accuracy is commonly considered to be about 1 percent. Of course, as the brightness diminishes the accuracy decreases. As I understand your letter and drawing, the two fields are not perfectly juxtaposed but are perceptibly separated. This would diminish accuracy considerably. I do not believe I can estimate within a few percent the accuracy of a brightness comparison with the set-up you describe. However, I do not see how such comparisons of brightness could be accurate within several percent unless a very large number of readings were made and averaged. If your intensity of illumination is very low, I believe Fechner's constant would be of the order of magnitude of 3 percent, even when the fields were perfectly juxtaposed.

"If I understand the set-up correctly, I would be inclined to estimate that, if you have very low brightnesses, the error of brightness match would be of the order of magnitude of 5 or 10 percent "

Perhaps it is not so bad as this. It would be interesting, however, if someone who understands the Foucault test would work out an answer to the question whether zonal readings expressed in thousandths of an inch mean something, or are largely illusory.

IN the June number we mentioned that Richard Perkin, 122 Chester Avenue Garden City, New York, would act as a sort of informal "committeeman" to ascertain how many would buy 20 inch mirror disks of Pyrex, if such combined purchasing would result in a lowered price. Mr. Perkin received many inquiries and has now obtained a quotation on Pyrex disks, 20-1/2 by 3-inches in size, in lots of six, of 85 dollars-a reduction of nearly one half from the ordinary price. By the way, Mr. Perkin is not a dealer, but an amateur who undertook to do this little job as a kindness. Evidently some thought him a dealer. He received a total of about 50 inquiries, to which the above is his answer.

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