ROSE TOOLS having petals which are tapered, in contradistinction to I tools similarly used for local correction of optical surfaces but which are simply channeled in the normal manner, turn out to have been the invention of the famous "Uncle John" Brashear. Mirror makers have used such tools for years but their origin has been lost sight of. Porter, in "A.T.M.," 64, describes such a tool.

The rediscovery of the rose tool's origin happened thus: G. Dallas Hanna, a San Francisco advanced amateur mentioned having come across "an interesting paper" in Volume 33 (1884) of the Proceedings of the American Association for the Advancement of Science, and when this paper was looked up it was found to contain evidence that Brashear invented that type of tool. Background is supplied by Brashear's "Autobiography."

In 1872 Brashear, then a steel mill worker in Pittsburgh, started a 5" objective lens as an amateur, broke the crown lens while polishing it, started again and finished the telescope. In 1877 he started a 12" f/10 mirror, finished it but cracked it while silvering, but made another. (At that time he found "Burton's Method" of silvering the backs of looking glasses described in Scientific American, modified it, and this was the genesis of the Brashear Method of fame.) In 1880, while still laboring in the steel mill, he inserted in Scientific American, October 30, the tiny advertisement here reproduced. "Alas for me!" he writes, "Hundreds of inquiries came to me from that advertisement;" such a market vacuum in telescopes existed at that time in this country.

By Christmas Brashear had shipped three mirrors but, working daytimes in the steel mills, spare time on optics, he underwent a breakdown. The Pittsburgh philanthropist William Thaw . saw him, liked the cut of his jib, gave him an equipped new shop, paid off his home mortgage, and told him to do optics whole time.

By 1884 Brashear "had invented and successfully used for several years a method of correcting the local errors in optical surfaces which proved to be very efficient" ("Autobiography") and which "has been used by many of the best opticians of the world..." He was invited to read a paper before the scientists of the nation and did so in 1884, its title being "The Production of Optical Surfaces." This paper is not merely a historical curiosity; it lucidly presents instructions of as great practical application in 1946 as in 1884. The paper:

IT is the purpose of this paper to describe briefly a new method of producing accurate optical surfaces, both plane and curved. The hand and machine methods of past and present workers in this line of research should not be forgotten, especially Foucault's method of local correction and Dr Draper's excellent modification thereof.

In order that the new method may be more clearly understood, attention is called to the serious difficulties met with in producing regular surfaces with the ordinary forms and methods of using local polishers. It is quite well known that the tendency of all local retouching is to leave on the surface of the abraded material what may be aptly called residual errors. This may be readily understood by the following illustration.

Suppose in the sectional view, Figure 1, we wish to work down the high zone, a, in an over-corrected surface A local polisher is worked over the high zone, either by hand or machine, of a size corresponding with the breadth of the zone and usually circular in outline. The result of this local abrasion is seen in Figure 2 in which the zone, a, Figure 1, is seen to be broken down, but generally the residual zones, b and c, are left incompletely abraded by the edge of the local polisher, which must afterwards be abraded by a larger polisher, which may or may not introduce new periodic or systematic errors. Dr. Draper seems to have overcome this tendency in a great measure by the use of the machine described in his monograph. After many experiments and much careful study of these zonal errors, I endeavored to eliminate them with a machine constructed so as to give an intricate motion to the polisher, a motion that would scarcely return into itself in many thousands of strokes. Notwithstanding the fact that this machine produced a number of excellent curves, it could not be depended upon, for h spite of the intricate interlacing of the polisher, zonal errors would creep in. After six years of labor. I reluctantly gave up the pursuit in this direction. From the fact that occasionally good results were produced by the machine, I was led to a careful study of the forms of polishers, and after three years of experimental work, I have been led to this conclusion: that, given a properly shaped polisher, surfaces of the highest excellence may be produced; either by hand or machine work, and that the simple rotary and reciprocal motions are all that are necessary to be given to the polishing tool.

I will now give as briefly as possible the leading features of the method which I have found so sure and certain in its results, by which not only ional errors are overcome, but by which any desired curve may be given to the optical surface under treatment. As it is necessary h all optical work to get the highest attainable polish, the first polishers are made h the ordinary form, i. e., with square or circular facets equally distributed over the surface of the tool, as shown h Figure 8. This is done to expedite the polishing. When the polish is brought up to the best (the best polish is no doubt the finest scratching we are able to do) the glass is allowed to come to a normal temperature, and is then studied by the admirable methods devised by M. Foucault for curved, and by Stehheil and Dr. C. S. Hastings for flat surfaces. Very seldom are the surfaces found free from defect. In order to clearly understand the method which I use for the correction of errors in producing a regular curve, let us take the former case of Figure 1, where the Foucault test shows a decided overcorrection or hyperboloid of revolution on the concave surface. The zone a is to be depressed and at the same time new errors, especially zonal errors, are to be avoided. The iron tool, which is of the same diameter as the surface to be worked, is laid off into six points diametrically opposite with the dividers set to the radius of the tool; as in Figure 3. The tool is now warmed and the pitch is spread over the leaf-like spaces, which are given the proper curve by being pressed down on the (previously wetted) concave surface. The pitch and tool are now cooled quickly by an abundant flow of water. In the shaping of this leaflet lies the whole secret of success. The zone, a, Figure 1, needing the greatest amount of abrasion, the leaflet is made widest at that point, but h order that no zonal errors may be introduced, as in Figure 2, it is gently tapered h each direction, the amount of taper being somewhat governed by the amount of lateral stroke given to the polisher, as well as the amount of departure of the zone from the normal curve. After the proper shape is given to the correcting or figuring tool, the pitch is again slightly warmed, pressed on the wetted surface, laid aside for an hour or so and the work of correcting or figuring is then begun. When the polisher has worked long enough to transfer its own peculiarities to the surface under treatment, the glass is allowed to come to a normal temperature and again tested. If any change in the shape of the leaflets is needed, an inspection of the surface will indicate the character of the change required.

Cooper Key many years ago graduated- the square facets of his polisher Elliptical, ring and other forms of polishers have been tried from time to time with varying success, and I have myself tried many forms, but with none have I had such uniform success as with the form which I have just described. It has all the advantages of a local polisher without its defects, and as these leaflets can be so readily shaped, and so easily manipulated, we have a ready means of giving any desired form to the optical surface we are manipulating. Figures 4, 5 and 6 show the various forms of these polishers which are designed to correct different forms of errors. Figure 7 shows a polishing or figuring tool which will give fine results, when time is not an element in the work. Such a polisher would break down almost any form of irregular surface, and give a regular curve, the kind of curve—oblate spheroid, spherical, elliptical, paraboloid or hyperboloid, depending on the length of lateral motion given to the polisher; indeed almost any idiosyncrasy which a curve may present can be successfully treated with a slight modification of this form of polisher.

Flat surfaces may also be treated by modifications of the same general form of tool, and overworking the edge zone, so difficult to avoid in hand polishing, can be readily and easily overcome.

It is beyond the limits of this paper to discuss the various difficulties which the practical optician has to deal with besides those noted, but I would mention one thing that seems to be an insurmountable barrier to the production of an ideal optical surface, in the lack of homogeneousness in material. It is a fact well known to everyone who has to deal with minute measurements that no two pieces of glass, speculum metal or other optical material made by artificial means are ever absolutely homogeneous when they come into the hands of the optician; hence every piece of material must have its special study, and in many cases idiosyncrasies present themselves which say "Thus far shalt thou come, but no farther."

If, in this brief paper, I have said anything that will add to the interest of this study, intimately associated with the names of Newton, Herschel, Ross, Lassell, Foucault, Nasmyth, Dr. Draper any many eminent opticians of to-day, I shall feel more than repaid for my work.

END of Brashear's paper. In it, he mentions the Draper modification of Foucault's method of local correction This was described in Draper's paper "On the Construction of a Silvered Glass Telescope," 1864, in Volume 14

of the "Smithsonian Contributions to Knowledge." That paper was reprinted in the Smithsonian Contributions in 1905, Volume 34, as well as in Scientific American Supplement, July 29, August 5, 12, 1905. There Draper described his machine, the one shown in "A.T.M." 165, as a simplification of Lord Rosse's and Lord Rosse described that machine in 1840 in the Philosophical Transactions of the Royal Society of London.

There are a number of these old classical papers pertaining to telescoptics. For example, Lassell on "Polishing the Specula of Reflecting Telescopes," Philosophical Transactions 1875; Ritchey on the "Two-foot Reflecting Telescopes of the Yerkes Observatory," in The Astrophysical Journal, 1901; and Ritchey "On the Modern Reflecting Telescope, and the Making and Testing of Optical Surfaces," from the "Smithsonian Contributions to Knowledge," 1905—all of which are out of print and to the average reader out of reach. Much of their content is obsolete and they are also too long to reprint in the present place. Some o£ them and others may, however, be reprinted in a sequel to "A.T.M." and "A.T.M.A." which has been planned, as sources of scattered pointers. It is difficult to estimate in advance how readers would regard these things. On the one hand, if you had the originals of these classics by your side would you read them? But if you had been asked to pay the added cost of including them in a book partly of original contributions, as in "A.T.M.A.," at about two cents a thousand words, would you then be critical? Please apply the same test to the inclusion of selected reprints—those of potential usefulness to telescope makers—from two decades of the present department and cast your vote.

Theoretically, all this matter may be looked up in large libraries but the difference between that and having the same things within the covers of a single volume, one's own, permanently available at home to pick up, dip into and throw down at any time, without strings attached, is almost absolute.

Your advice about this book is solicited and, as usual in human affairs, will be followed if it is liked.

When the shades of night have fallen
But the seeing's very bad
Other views may oft be had.
Sometimes a celestial maid
Has forgot to draw the shade.
Thus, from studies astronomical
One can turn to anatomical.

Albert H. Johns, Larchmont, N. Y., speaks feelingly in light verse:

The kitchen floor knee deep in pitch—
To make a lap 'e'd 'ad an itch.
"I'll build a telescope," 'e said.
(When young, 'e'd fallen on 'is 'ead.)

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