NOVELTY FOR NOVELTY'S sake can easily be argued down by cold logic but, who wants to be too logical when a hobby is involved? Recently your scribe, in mining down through the Archeozoic strata of a desk filled with many years' accumulations of telescoptical lore, in search of an elusive file of papers, hauled out the following item dated 1939. No apology is offered for its age; some ageless and fascinating items lurk in the same place.

The present little item came from C. H. Helm, an electrical engineer Blidahlund 1, Chrl., Copenhagen, Denmark. He says he bought "A.T.M." in 1928, when living in the U. S., made a 10" Cass, returned to Denmark, forgot optics for 9 years, then made five concave grating mirrors for the Academy of Science at Stockholm, made a Fabry-Pérot interferometer for the University of Lund, with mirrors worked to 1/50 wavelength (and sends a ronchigram to prove it), also made two mirrors to 1/50 wavelength for the famous Danish physicist Bohr.

The idea offered by Helm is shown in the figure-a modified Gregorian for terrestial use. A is the usual paraboloidal primary. B is a secondary, also paraboloidal and adjusted to return the rays as parallel light. CD is a small telescope, like field glasses, adjusted to infinity. The parallel lines represent a tube to exclude extraneous light. "It works all right," Helm reports. He reports also that "A.T.M." is "the best book ever published on any one subject," which may be slightly hyperbolic but is pleasant to hear.

Commenting on Helm's ideas, N. J. Schell, Beaver Falls, Pa., says "Have never seen just this before, but the secondary acts similar to an erecting lens if used in this fashion. The rays would be parallel to the axis only on an object in line with the axis, all others being inclined from the axis at angles corresponding to the entrance (or incoming) angles. This would tend to limit the extent of the field to the proportions of the secondary. The arrangement would serve somewhat along the lines of Dall's 16" spherical Cass, which has the secondary focus between the mirrors, but since Dall's is á-la-Cass, the size of the field available would be larger with a given size of secondary. Dall's also gives an erect image.

"Two or three years ago, at the request of the late Dr. Palmer of Pittsburgh," Schell continues, "I suggested to him a Cass with a secondary designed and figured to have a secondary focus at infinity, for a special purpose he had in mind. This has no bearing on Helm's design, except to indicate that the idea of infinity secondary focus, having occurred to me, probably has occurred to many others as well.

"However, if this has any advantage not readily apparent, it might be worth developing further."

One function of this department being to put ideas on public record, the above idea is hereby put on public record. In fact, not enough of those proposed to this department have been similarly put on such record-they hide in special files of old letters in the above-mentioned desk, and every now and then some new worker rediscovers them and proposes them, which then sets in motion a search. The variety of telescoptical ideas hit on by amateurs during the past 10 years has been astonishing.

IN A TINY NOTE in this department in July, 1942, mention was made of the death of J. H. Hindle, co-author of "A.T.M." and of "A.T.M.A.," and promise of further facts was made. At long last, and despite the complications of the war, data have now come to light in the form of an obituary contributed by William Porthouse, of England, to the famous "M.N.," or Monthly Notices, of the Royal Astronomical Society, principal organ of British professional astronomers. Hindle was an amateur but, just as several amateurs enjoy membership in the professionals' American Astronomical Society, so was Hindle regarded by British professionals as properly belonging to both groups. The Monthly Notices is a magazine of scope solid substance, abstruse depth and height, similar to our American professional astronomers magazine, The Astrophysical Journal. The obituary:

"John Henry Hindle was born at Edenfield, in the Rossendale valley of Lancashire, of Scottish stock, on 1869 November 2, and was elected to Fellowship of the Society on 1922 June 22.

"He was a shrewd Lancashire ironmaster, generous of heart and hand, with all the many virtues of his race: a man of robust intelligence, inexhaustible patience and infinite resource. At the date of his death he was the governing director of the firm Hindle, Son & Co., Ltd., Engineers, of Witton, Blackburn, where he produced, based on his own and his son's patents, electric and other baling presses, and powerful wide looms for the weaving of cotton and woolen dryer felts for use in the paper-making industry. He was indeed the first person directly to apply electrical power to the generation of mechanical pressure for baling loose materials, and the convenience of this machine has been widely recognized.

"Apart from elementary education at the local school at Edenfield, Hindle was practically self-taught At the age of 12 years he commenced work as a 'half-timer' in the textile industry, and upon leaving school at the age of 13 went into the mill office where his father was secretary and cashier. During this period he worked in an iron foundry and workshop in his spare time and developed very early his interest in engineering, particularly on the electrical side. About 1895 he had attained the position of electrical consultant on hoisting machinery and electrical motors and dynamos. He developed and patented automatic control gear, an electro-magnetic brake and an emergency safety mechanism for use in electric passenger and goods lifts.

"In 1910 he courageously started in business for himself as a practical engineer in Manchester, removing in 1918 to Haslingden and afterwards to the present Union Engineering Works, Blackburn, where, with the assistance of his only son Thomas, who survives him, he built up a considerable business in textile engineering.

"As his major hobby the production of telescope mirrors appealed to him because of his love of the delicate and precise in science and art. Although not physically a big man he had a wonderful facility in the handing of large specula. Some years ago he was described in the Manchester Guardian as 'one of the leading optical experts of the time.' He produced and mounted many Newtonian and kindred mirrors of all sizes, the largest being.the 20-1/2" made for Dr. W. H. Steavenson, the 25" which he used himself for the delight of his friends, and the 30" which is being mounted at the Cambridge University Observatory by arrangement with Sir Arthur Eddington. This instrument is to be available for the Observatory staff until such time as Dr. Steavenson is free to put it to full use. It is described in detail by Hindle himself in Scientific American for 1939 September. Notwithstanding the magnitude of these instruments Hindle always considered himself a 'pure' amateur, never profiting financially by his hobby, but always shrewdly placing his telescopes where he knew they would do the best work.

"His principal contributions to the craft were:-(a) 'The Compound Telescope-Cassegrainian and Gregorian Types.' (b) 'The Mechanical Flotation of Mirrors.' (c) 'How to Make a Diagonal for a Newtonian Reflector.' (All appearing in permanent form in 'Amateur Telescope Making' and 'Amateur Telescope Making-Advanced.') (d) 'A New Test for Cassegrainian and Gregorian Secondary Mirrors.' (M.N., 91, 592, 1931.)

"This new test was considered by Professor Sampson to be a great improvement on other practice, and led to Hindle's being commissioned to make a new 19-1/2'' convex secondary for the 72" reflector at the Dominion Observatory, B. C., to be subjected to the new test. I cannot find, however, that this convex was actually completed.

"Hindle designed his own 'ovoid stroke' grinding and polishing machine' but refused to patent it. It is described in 'Amateur Telescope Making' and it has become justly popular in the United States of America. A machine of its type is installed at the Kyoto Imperial Observatory, Japan.

"Hindle was a world-wide traveler. His unique business took him constantly to the Continent. He visited South Africa, the United States, and Canada, the last two on many occasions. At such times he always made it convenient to visit the great observatories where his acquaintance with the optics of reflection made him persona grata with those in control. He was present at the pouring of the 200" disk for the Mount Palomar reflector, an experience which he afterwards described to the; present writer in vivid phrases and good Lancashire accent.

"Hindle died at his home in Blackburn on 1942, May 17, at the age of 72. He is buried with his wife (who predeceased him by 22 years) in Helmshore churchyard and his memorial bears the simple inscription of his devoted daughter, who survives him: 'He helped them to look at the stars."'

Your scribe recalls several protracted visits made by Hindle in New York for business purposes. The "good Lancashire accent" is closer to American than the so-called "standard" English.

He was a thick-set man who, despite his descent from Scottish stock, reminded one of the chunky, substantial John Bull of the familiar sketches, and he was a bit "set." His Scottish stock came to the surface in a long but exceedingly lively argument which he conducted with Ellison in English Mechanics in 1926, regarding the effects of changing temperature in telescope mirrors In issue after issue the Englishman of Scottish descent and the sometimes peppery Irishman of Scottish-English descent did major combat, barring no holds. Your scribe still has most of these serial communications- a dozen rounds of pitched battle, each provocative of many a chuckle-preserved in a treasured file clipped from English Mechanics. Few of us are wholly logical when it comes to higher authorities. We incline to place them beneath the haloes of saints. Most of them would prefer to be regarded only as people, and these two were very human.

CYRIL G. WATES, 7718 Jasper Ave., Edmonton, Alberta, Canada, writes:

"With reference to J. R. Haviland's note on the Barlow lens in the September, 1943, issue, the following points may be of interest. The amplifying power of any Barlow is given the formula using the same notation as in Haviland's equations. The focal length of the lens is the principal factor in determining the amplifying power.

"While it is true that the position of the lens has some bearing upon the magnification, the result of moving the lens within reasonable limits is very small. In the example given the lens is placed 2" inside the prime focus, giving an amplification of 4. With the lens 1" inside prime focus, A is 3.8 with the lens 6" from prime focus, A is 5.

"As a rough method of determining the correct focal length of the Barlow lens and its position in relation to the prime focus, the following formulas are approximately correct. No exact formula is possible, since each factor depends upon the other.

"The 'power' of spectacle lenses is given in diopters, and the amateur who wishes to experiment with a Barlow lens purchased from his local optician should ask for a negative lens of 39.4 divided by in inches."

READERS of this department have inquired about the cause of rough, porous, or flaky aluminum coatings that have sometimes been found on telescope mirrors. The question was submitted to an outstanding authority on aluminizing and he replied that this is often a case of what he called "measles," due to faulty cleaning of the mirror before it is put into the jar for coating, or to greasing up in the "evaporatus" after the mirror is put m before mirroring.

An independent means by which the recipient of an aluminized mirror may evaluate the job done consists, as described in a private communication from the authority just mentioned, in pressing a little strip of scotch tape onto the edge of the aluminized surface. If the latter is correctly mirrored the scotch tape will not, when pulled off, remove any of the aluminum film.

On the other side of the question. some who have aluminized mirrors have been blamed unjustly for imperfect coatings of another type, that were caused by pits left in the polishing by the mirror maker himself. Many mirrors-a very great many-especially first ones but sometimes subsequent ones, are not polished out. No aluminizer can be even remotely expected to cover over these faults; in fact, the coating will make them appear to be much more prominent than they appeared before.

Those, also, who hurry the aluminizer, asking immediate return of the mirror sent him, run risk of receiving a case of measles, especially if the job has been done in damp weather, when there is a tendency for oil to creep into the chamber. The disease does not always appear at once but may have a gestation period of a few days. If, therefore, the aluminizer is given a few days to age the mirror before he ships it back, the latent measles, if any, may show up and be cured by recoating.

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