The Mirror-Making Notes of Sir William Herschel: An Introduction By Matthew Considine, August 2002 http://www.considine.net/mac/wmherschel/dublin2002.txt Sir William Herschel (1738-1822) needs no introduction. An accomplished musician, mathematician, and astronomer, he has been the subject of a number of biographies . In addition to composing works for the oboe, submitting papers on a range of topics to the Royal Society of London, William Herschel discovered the planet Uranus and catalogued a number of non-stellar objects. Along with his sister Caroline and his son John, he was a member one of the premier scientific families of England. Unfortunately, his mirror-making notes do need an introduction. If for no other reason than the fact that they have been unpublished and generally unexamined for the last 200 years, then for the fact that William Herschel was self taught, the materials left behind merit attention: In Transactions Optical Society, No. 4 for 1924 -- 25, Dr. W. H. Stevenson, F.R.A.S., outlines "A Peep Into Herschel's Workshop.: Sir William Herschel left four complete volumes in manuscript, relating to his processes and experiments, in which he sums up the results of 40 years of experience in telescope making. These manuscripts are now in the hands of the Royal Astronomical Society, and, says Dr. Stevenson, "it is greatly to be desired that means should someday be found for publishing them." (Here's an opportunity for some generous amateur enthusiast or group of enthusiasts-editor.) To date, the best published use of this material has been made by J. L. E. Dreyer , followed by J. A. Bennett . In Dreyer's work, however, the primary aim was a biography, while the goal in Bennett's article was to discuss Herschel's telescopes. Additionally, both works are relatively difficult to come by. And neither was an attempt to chronicle the methods Herschel used in casting, grinding and polishing specula. In fact, regarding the notes' lack of publication, Bennett writes: "It is not clear why the results of Herschel's polishing experiments were never published. … By January 1805 Herschel had written 'a work on the subject of making mirrors for telescopes of all sizes, in which the method of giving them not only the parabolic form but any other of the conic sections that may be required, is explained with perfect clearness and supported by several thousands of facts', and was beginning to arrange its publication by the Royal Society, see RAS MSS Herschel W.1/13.B.126; 1/1, p. 257." A desire to understand Herschel's learning curve, coupled with the above passage from "Amateur Telescope Making", has prompted this author to undertake the task of transcribing and publishing Herschel's notes. The aim of this paper is to provide an introduction to the mirror-making notes held by the Royal Astronomical Society, present a finding-aid suitable for use with the microfilm copies of this material, and to provide some observations gleaned from an initial review of the notes. Also, the status of the current transcription process will be given, as well as some ideas for augmenting the work once it is completed. Background Sir William Herschel was a self-taught instrument maker. Having come across a copy of Ferguson's astronomy in the late 1700's and then having had the opportunity to observe with a small telescope , Herschel was bitten by the astronomy "bug". Like others before and after him, however, he soon longed for an instrument capable of revealing more. Upon inquiry to opticians in London, he found that it would be both expensive and time-consuming to get a larger instrument. Rather than purchasing an instrument, he resolved to build his own. Seeking out a gentleman in a nearby town who was known to make mirrors, Herschel took some lessons and eventually bought the gentleman's stock of material and equipment. (Unfortunately, it is not known who this gentleman was, for it seems that he must have been fairly accomplished and worthy of some documentation.) Armed with some raw material upon which to work, some tools, and a small amount of experience gained from the lessons, Herschel began making his own mirrors. Here, his penchant for note-taking proved valuable, for early on he began to record the results of his efforts. The result was a step-by-step chronicle of his learning curve, allowing him to benefit from mistakes than he would if a less structured approach to the task were adopted. As we know, he was successful in making telescopes of that were well-regarded, using them not only for his own purposes and discoveries but providing them to others. At the same time, with the discovery of Uranus and the generosity of the king at the time, Herschel was able to devote himself exclusively to astronomy and telescope-making. Part of the notes he kept contained a treatise on the construction of mirrors. This seems to have been the end goal of his note-taking efforts - to create a systematic approach to create a mirror with specific qualities. The preserved material The notes preserved at the Royal Astronomical Society have generally not been reviewed by many people. Horace Dall is one example of a telescope maker who made trips to review the notes at Oxford (though the copies held there are not believed to be complete). No doubt others similarly reviewed the material. J. L. E. Dreyer was one notable example. In his two-volume work he provides as part of the biography of Herschel a description on his techniques. While not a verbatim transcription of Herschel's notes, it has provided the best insights to date. Yet even Dreyer admits that a more thorough discussion was warranted. Further, Dreyer's two-volume work today is difficult to find. So, from the perspective of many involved in telescope-making - and certainly from the perspective of the amateur - Herschel's notes have remained unpublished and essentially unexamined. At present, the original papers of Sir William Herschel can be found in the collection of the Royal Astronomical Society. On microfilm, they are available in a handful of libraries. In 1978 in volume 85 of the Memoirs of the Royal Astronomical Society James Bennett provided a catalog of the archives and manuscripts then held. This issue of the Memoirs is also difficult to find as they ceased publication after this point. (Note that the memoirs are different from the Monthly Notices of the Royal Astronomical Society, which of course are still being published.) Quoting from the Bennett catalog: "The Herschel collection is divided into four sections: papers of Carolyn Herschel of John Herschel, of William Herschel and books and papers from the Herschel family which cannot fall into one of these groups. The contents of the miscellaneous section had not been listed in full except for books which have belonged to Carolyn John or William. The books containing indications have been included, as appropriate, under section C., J. or W. Almost all material in this collection has been donated by members of the Herschel family. In 1866 John Herschel gave the society the four volumes on his father's registers sheets of double stars and copies made by Carolyn on the sweeps with 20 ft. telescope. John Herschel also gave a series of manuscripts star charts by himself but unfortunately these kidnapped now be located. In 1918 dryer was invited to selectmen description of families collection which the society would value in W. H. Stevenson admitted further selection in 1943 some additional material has recently been donated by Mrs. E. Shoreline." This collection has been microfilmed and the Carolyn, John, and William Herschel papers can be found on 24 reels. (Note there is a separate archive of Herschel correspondence belonging to his son John, which is in a separate microfilmed collection.) In my search, it was not apparent that a mapping or finding-aid to the reels existed. This was the first task that needed to be accomplished and was done over several weeks. The 24 reels begin with material belonging to Carolyn Herschel. This is found on Reels 1, 2 and the beginning of Reel 3. Of possible interest is Reel two which appears to contain a photocopy of Carolyn Herschel's incomplete autobiography. The original is listed as being in the possession of Mrs. E. Shorland, but that may have subsequently changed hands. The material in this collection pertaining to John Herschel begins on Reel 3 and extends to and includes Reel 11. William Herschel's material begins on Reel 12 and continues through to the end at Reel 24. Beginning on Reel 12 is Sir William's correspondence, which extends to the beginning of Reel 14. Also beginning on reel 14 is his journal of observations. His observations continue through to the end of Reel 17. Beginning on Reel 18 are copies of papers, as well as calculations and observations relating to the subjects of those papers. For example, observations on the transit Mercury, an account of the discovery of the sixth and seventh satellites of Saturn, and similar items like this can be found throughout the remaining Reels until we get to Reel 21. Beginning about halfway through real 21 is the section on telescopes. This is the material that is currently being transcribed. Items 5/1 to 5/11 are found on Reel 22. Items 5/12 are found on Reel 23. Entries beyond 5/13 are found on Reel 24. Following the numbering scheme adopted by Bennett, the telescope-related items on the Reels are as follows: Reel 21 5/1 description of the lamp micrometer and the method of using it (paper) 5/2.1 description of 40 feet reflecting telescope (paper) 5/2.2 calculations and notes are relating to the above paper 5/2.3 A copy of the printed version of the above paper (first pages on microfilm) 5/2.4 another copy of the above paper (not on the microfilm?) 5/3.1 on the powers of penetrating into space by telescopes (paper) 5/3.2 calculations relating to the above paper 5/3.3 part of a letter in reply to criticism of the above paper and three alterations 5/4.1 experiments for ascertaining how far telescopes will enable us to determine very small angles (paper) 5/4.2 calculations relevant to the above 5/5 drawings of telescopes. There are 13 drawings of 7 ft., 10 ft., small 20 ft. and large 10 ft. Some of these were done by William Watson 5/6 a users manual for the 7 ft. telescope 5/7 another users manual for 7 ft. telescope this being a photocopy of original in a possession of a A. C. Sanderson 5/8 user manual for large 10 ft. telescope 5/9 user manual for the 20 ft. telescope 5/10 bills expenses for the 20 ft. telescope includes directions for on packing the cases and an item station of the contents of the cases 5/11.1 contents of boxes for parts of 25 ft. Herschel and telescope (5/11.2 "woodwork belonging to the above telescope" is not on the microfilm) 5/11.3 directions for the management of the 25 ft. telescope The next section encompasses the material directly related to mirror-making and this is the primary interest at present. Reel 22 5/12 experiments on the construction of speculative see dryer page 552 5/12.1 volume 1 covers experiments conducted from 1773 to the 28th of November 1790 5/12.2 volume 2 cover is the second of December 1790 to the 16th of December 1793 5/12.3 volume 3 cover is the 20th of December 1793 to the 4th Jan. 1804 5/12.4 volume 4 covers the night to Jan. 1804 to the fifth of December 1818 5/12.5 there is indexed articles contained in the four volumes of experiments 5/12.6 there is second index to the same degree 5/12.7 a listing of what were considered to be successful experiments arrange for each mirror size according to the succession of volumes in numbers 5/13 the treaties entitled on the construction of speculative taking up by folders see dryer page 553 5/14 the second treaties entitled results of experiments on the construction of merits for telescopes 5/14.1 this document results of experiments is unique folders 5/14.2 going with this document are 59 drawings of grinding machines made by John Herschel under William Herschel's inspection Reel 23 5/14.3 large number of slips of paper carrying results from experiments in the construction of speculative arrange and bundles by subject from which the sections of this treatise has been created A note in the catalog mentions that item "3/4" on the transit Mercury contains a section entitled "observations experiments relating to the causes which often affect yours is to prevent their showing objects distinctly." This paper - and many others printed in the Philosophical Transactions - can be found online at http://bnf.gallica.fr. In the remaining Reels there are some miscellaneous items of interest. There are papers and calculations regarding the nature of light high-end invisible raisins on ID into red light are also some loose papers entitled philosophical experiments 19 sand being experiments to be made. There is a photocopy of editorial page of notes by one Herschel experiments concerning strength of glass there are also some loose notes always page of notes undercover mark bike your own Herschel and that they should abandon there were slated to be thrown out the there also miscellaneous collection of papers as well as a copy of buyers kept by William Herschel and various torch 1791-1817 interestingly among these is a description of it before he took through England and the notes that he made on glass kind grained grinding machines. Observations In reviewing Herschel's notes a couple of things catch one's attention: 1: While probably most associated with speculum metal, Herschel also experimented with glass as a mirror. But he found it useful only for solar observations as he had no way to increase the reflectiveness of the surface. Nevertheless, he certainly recognized the merits of the material, vis-à-vis ease of polishing: __ A glass mirror to reflect light from the first surface takes a high polish and fine figure, it is of use in solar observations A 3.589,2. B 3.648,8. 2: While Herschel is probably best known for his Newtonian telescopes and the so-called Herschelian reflector, it is also quite clear that he ground mirrors for Gregorian telescopes. At least one was for a Professor Wood. There are also references to making mirrors and objectives for microscopes. It would be a worthwhile exercise to track down instruments such as these, inasmuch as a couple of authors have suggested that some mirrors were probably not made by Herschel. However, there is no evidence offered to suggest why this would be the case, other than their quality leaves something to be desired. 3: The notes also detail Herschel's testing methods, whereby he evaluated a mirror by looking at the quality of an image in three zones. Given his attention to detail and his interest in experimenting, one wonders how close he came to realizing that he was viewing the surface of the mirror as a deviation from its desired curve. And given the following observation, just how far away from discovering the knife-edge test was Sir William Herschel? __At double the focal length and holding a straight white narrow piece of board, so as to make it pass in succession over the mirror, blotches or lunar appearances will be perceived that would otherwise have escaped notice. C 3.319,5. 4: Among the miscellaneous papers is what appears to be a "to do" list showing how telescope-construction labor was divided among various people. There is also a note from the Pitt Brothers with respect to expenses for the mounting (called "machine") for a 20 foot telescope. The lack of drawings for optical tube assemblies or mounts prompts one to wonder how much he sub-contracted this design work, or relied on the mounting schemes of others before him. 5: Herschel's eyepiece manufacturing may have been carried out using the Della Torre procedure, as there are no specific notes or experiments discussing eyepieces. (See Appendix II) As this paper was translated by him early in his telescope making career (1781)it perhaps stands to reason that this is the method he used for creating his eyepieces 6: Other experiments which Herschel carried out involved the use of binocular vision, thin mirrors, and a variety of polishing materials and mirror substrates. This leads one to the conclusion that Herschel must certainly have viewed the insight he gained from his experiments as a trade secret. It is not surprising, then, that he never published any material detailing how he made his telescopes. In 1787 he did send to the Royal Society a short paper that described some of his efforts in constructing specula, but he never published the paper. (In fact, it has only been found in Dreyer's two volume work "The Life and Scientific Papers of Sir William Herschel.") So it makes one wonder which audience Herschel had in mind when he wrote his treatises. Were they intended for his son, should he continue with the business? Or did Herschel intend to publish them despite the fact that he essentially ran a telescope-making business? Status At present (August, 2002), approximately half of one of the treatises has been transcribed. This actually represents a substantial portion of the second treatise as well, since that is an expanded version of the first treatise. All of the images have been taken off of microfilm and put into a format that is easier to work with (e.g. hardcopy). While the handwriting is generally not difficult to read, the use of archaic or obscure words has necessitated the creation of a glossary. This will facilitate an easier analysis of the notes, once both treatises have been transcribed. Additionally, the treatises contain references to specific experiments that were conducted and from which some conclusions were drawn. Ideally, these will be transcribed at some point, and linked into the current document being developed. Also, there may be some material on Reel 2, under the Caroline Herschel collection, which has some bearing on Herschel's telescope-making techniques. Dreyer alludes to a selection of miscellaneous papers that may contain the Della Torre letter and a couple of other items that, while published by Dreyer in 1912, do not appear to be on the reels with the other William Herschel material. Finally, the machine drawings of JFW Herschel will need to be redrawn for the sake of clarity and labeling. Suggestions for future work It seems that a broader audience would benefit from more accessible versions of Dreyer's work and Bennett's catalog. At the very least, the Bennett catalog merits an electronic or "online" version, to make future research at the R.A.S. easier. A significant body of correspondence from and to John FW Herschel exists in a number of collections. Although spread out, this material has been reviewed and categorized by Prof. Michael Crowe. Reviewing Prof. Crowe's work, one sees a number of items pertaining to telescopes, mirrors and mirror-making. It would be valuable to track down each of these letters and review them in the context of Sir William's work. With the addition of Caroline Herschel's perspectives, the result would be a more comprehensive analysis of Herschel-family mirror-making knowledge. Lastly, the papers of W. H. Steavenson are - according to the Bennett catalog - on file at the R.A.S., but were not catalogued. Given Steavenson's articles on Herschel, it would perhaps be useful to see if any unpublished material exists that would shed light on his analysis of Herschel. Conclusion The albeit brief discussion above is meant to serve as a description of the William Herschel mirror-making material preserved at the R. A. S. and to provide the backdrop for the current transcription process under way. If nothing else, it is hoped that this introduction shows that a significant contribution to the history and development of mirror-making techniques is still to be found in the Herschel material. Matthew Considine Doylestown, PA, USA August, 2002 Acknowledgments I am greatly indebted Peter Hingley, librarian of the Royal Astronomical Society, and to the Royal Astronomical Society itself, for help in gaining easier access to the material on microfilm and for granting permission to have the material published. Thanks also go to Peter Abrahams, for providing encouragement and assistance in getting copies of a number of articles that would have otherwise been difficult to find. In no particular order, the following have also been very helpful in answering questions and/or directing me to various sources : Prof. Michael Crowe, J. A. Bennett, J. Herschel-Shorland, Bart Fried, Jack Koester, and the members of the "oldscope" email discussion list. The American Philosophical Society was instrumental in helping to get copies of the relevant microfilm Reels. And the microfilm facilities at the Univ. of Delaware - though they don't know it - have been a great resource to use for film review. Lastly, my wife Melanie deserves credit for putting up with my time spent at the computer, the film reader, and for the muttering of words like "colcather" and "scabrousness." Bibliography Bennett, J.A. "Catalogue of the Archives and Manuscripts of the Royal Astronomical Society," Memoirs of the Royal Astronomical Society, Vol 85, 1978 Bennett, J. A., "On the Power of Penetrating into Space": The Telescopes of William Herschel", Journal of History of Astronomy, vii (1976), pp 75-108. Davies, C. D. P. (Rev.), "Herschel's 18 3/4 inch Speculum (the '20 ft')", MNRAS, pp23-26, 11/1923 Dreyer, "Description of ..", 1912, Monthly Notices of the Royal Astronomical Society. Dreyer, "The Life and Writings of Sir William Herschel. The scientific papers of Sir William Herschel, knt. ... including early papers hitherto unpublished; collected and edited under the direction of a joint committee of the Royal society and the Royal astronomical society, with a biographical introduction …" London, The Royal society and the Royal astronomical society, 1912. Herschel, C "Memoirs and Correspondence of Caroline Herschel" Herschel, W RAS MS Herschel, W. 3/4, 5, 6, 7 (Reels 21-24) Hysom, E. J., "Test of the Shape of Mirrors by Herschel," Journal of the History of Astronomy, xxvii (1996), pp 348-352. Maurer, Andreas, "William Herschel's Telescopes," JBAA, 1971, pp 284-296. Maurer, Andreas, "A Compendium of All Known Herschel Telescopes", J. Of the Antique Telescope Society, #14, Winter 1998 Rienitz, Joachim, "William Herschel's Mirror Test and its Consequences," Steavenson, W. H., "Herschel's first 40-foot Speculum", The Observatory, Vol. 50, no. 635, pp 114-118, 4/1927 Steavenson, W. H., "A Peep into Herschel's Workshop", Trans. Of the Optc. Society, Vol. XXVI, No. 4, pp 210-238, 1924-25 Steavenson, W. H., "The Herschel Instruments at Slough", The Observatory, Vol. 47, pp 303-308, 10/1924 Appendix I Table of Contents to Construction of Specula Main Sections 1 Structure of Mirrors. 2 Coating Mirrors. 3 Preparing mirrors for polishing. 4 Of Machines 5 Polishing stuffs. 6 Substances for polishers. 7 Requisites for polishers. 8 Size of polishers. 9 Construction of polishers. 10 Making polishers. 11 Gutters in polishers. 12 Scars 13 Stroke. 14 Round motion of the mirror. 15 Motions of the polisher. 16 Side motion of the mirror. 17 Eccentric motions. 18 Combined motions. 19 Position of the polisher. 20 Beginning the work of polishing. 21 Velocity of the polishing motion. 22 Method of supplying the polisher with polishing stuff. 23 Focal length. 24 Symptoms of the action of the polisher. 25 Adhesion. 26 Temperature at the time of polishing. 27 Mutual action of the polishers and mirrors in polishing. 28 To sharpen polishers. 29 To make polishers act. 30 Progressive examination of the mirror. 31 Incidental imperfections of mirrors. 32 Critical examination of mirrors. 33 Giving figure to mirrors. 34 Plain mirrors for Newtonian telescopes. 35 Distinctness of mirrors. 36 High polish. 37 Finishing the work of polishing. 38 Cleaning and preserving mirrors. 39 Of the adjustment of mirrors. 40 Selection of successful experiments. Results of experiments on the construction of mirrors Section I Of the structure of mirrors. 1 Of the aperture of mirrors. 2 Of the thickness of mirrors. 3 Of the weight of mirrors. 4 Of copper and tin mixtures. 5 Of Platina and other mixtures. 6 Remarks on different compositions. Section II Of coating mirrors. 1 Of Gages. 2 Of Patterns for moulding. 3 Of Moulding. 4 Of Casting mirrors. Section III Of preparing mirrors for polishing. 1 Of Grindstone work. 2 Of grinding Tools. 3 Of Emery grinding. 4 Of the focal length of mirrors. 5 Of edging the mirror. 6 Of refining the mirror. 7 Of the materials for refining. Section IV Of Machines 1 General remarks on polishing machines. 2 Of Handles for grinding and polishing. 3 Of polishing rings and claws. 4 Of Levers. 5 Of Rubbing bars and stroke stops. 6 Of Tail pieces. 7 Round motion of the mirror. 8 Round motion of the polisher. 9 Of the side motion of the mirror. 10 Counterweights. 11 Of pulling bars, 12 Application of powers. 13 Of cases for mirrors. 14 Of stroke indices. 15 Miscenllaneous apparatus. Section V Of polishing stuffs. 1 Of Colcathar. 2 Of Putty. 3 Of Soap. 4 Of several materials. 5 Of several Utensils. Section VI Of the substances for polishers. 1 Of Swedish pitch. 2 Of American tar-pitch. 3 Of Coal-tar-pitch. 4 Of Swedish & American tar-pitch. 5 Of Swedish and Coal-tar-pitch. 6 Of hard pitch. 7 Of soft pitch. 8 Of pitch & Linseed oil or Turpentine. 9 Of Rosin and Linseed oil. 10 Of Lamp black and pitch. 11 Of Shell Lac mixtures 12 Of other substances for polishers. Section VII Of the requisites for polishers. 1 Of glutinousness. 2 Of flexibility. 3 Of hardness. 4 Of softness. 5 Of a dragging quality. Section VIII Of the size of polishers. 1 Of Strap polishers. 2 Of the length of Oval polishers. 3 Of the breadth of polishers. 4 Of the ends of polishers. 5 Of round polishers. Section IX Of the construction of polishers. 1 Of the foundation of polishers. 2 Of the Trial of pitch. 3 Of the Trial of the method of work. 4 Of casting polishers. 5 Of different ways of making polishers. Section X Of making polishers. 1 Of giving figure to polishers. 2 Of figuring large polishers without a concave tool. 3 Of altering polishers. 4 Of preserving polishers. Section XI Of Gutters in polishers. 1 Of Cross gutters. 2 Of cutting gutters. 3 Of the arrangement & distance of gutters. 4 Of longitudinal gutters. 5 Of Star cut gutters. 6 Trial of different gutters. 7 Of gutters for action. 8 Of gutters for flexibility. 9 Of gutters for feeding the polisher. 10 Of gutters for high polish. Section XII Of Scars 1 Of cross Scars. 2 Of deep Scars or cross Cuts. 3 Trial of different Scars. Section XIII Of the Stroke. 1 Remarks on the Stroke. 2 Of a long stroke. 3 Indications of the proper length. 4 Of a short stroke. 5 Of a straight stroke. 6 Of the adjustment and measure of the stroke. Section XIV Of the round motion of the mirror. 1 Of the effect of the round motion of the mirror. 2 Of the direction of the round motion. 3 Of a round motion by the stroke. 4 Velocity of th round motion of the mirror. 5 Adhesion from the round motion of the mirror. Section XV Of the motions of the polisher. 1 Of the round motion of the polisher. 2 Of the vibratory motion of the polisher. Section XVI Of the side motion of the mirror. 1 General remarks on the side-motion. 2 Effects of side motion on the figure. 3 Effects of the side motion on the polisher. 4 Distinctness by side motion. 5 Effects of the Hourglass side motion. 6 Oval and other motions. Section XVII Of eccentric motions. 1 Of the eccentricity of the stroke 2 Of the effect of the eccentric stroke. 3 Of Lateral eccentricity. 4 Of eccentricity in the frame. Section XVIII Of combined motions. 1 Of combinations with the side motion. 2 Of the combination of the round motions. 3 Of the combination of the stroke, eccentri- city and round motion. 4 Of the combination of the stroke, the two round motions and the side motion. Section XIX Of the position of the polisher. 1 Of placing the polisher. 2 Of polishing over the small diameter. 3 Of polishing upon the mirror. Section XX Of beginning the work of polishing. 1 Of the necessary regulation of the work. 2 Of putting on a mirror prepared for the po- lisher. 3 Of putting on polished mirrors. 4 Of putting on a mirror of a different fo- cal length. Section XXI On the velocity of the polishing motion. 1 Remarks on the velocity. 2 Of velocities that have been used. 3 Remarks on the heat arising from the polishing motion. 4 Of the quantity of heat generated by the polishing motion. Section XXII Of the method of supplying the polisher with polishing stuff. 1 Of supplying the polisher by gutters and scars 2 Of feeding the polisher by addition of polishing stuff. 3 How to diminish the quantity of polishing stuff. Section XXIII Of the focal length. 1 Trial of the focal length. 2 To lengthen the focus. 3 To shorten the focal length. 4 To preserve the focal length. Section XXIV Symptoms of the action of the polisher. 1 Symptoms of the proper action. 2 Symptoms of Hardness. 3 Symptoms of Softness. 4 Variety of Symptoms. Section XXV Of adhesion. 1 Of the proper quantity of adhesion. 2 Of too much adhesion. 3 Of too little adhesion. Section XXVI Of the temperature at the time of polishing. 1 Remarks on the temperature. 2 Of too high a temperature. 3 Of too low a temperature. 4 Of the range of temperature. 5 Of changeable temperature. 6 Of artificial temperature. Section XXVII Of the mutual action of the polishers and mirrors in polishing. 1 Remarks on the mutual action 2 Of a want of reaction of the polisher. 3 How to obtain the reaction of the polisher 4 Of stubborn polishers 5 How to overcome stubborness. Section XXVIII To sharpen polishers. 1 Blunt polishers may be sharpened by restoring the gutters and scars. 2 By scraping them with a saw. 3 By scraping them with a sharp edge. 4 Of the time for sharpening. Section XXIX To make polishers act. 1 By sharpening them. 2 By management of the motions. 3 When the temperature is too low. 4 By additional weight. 5 Remarks on the time of action. Section XXX Progressive examination of the mirror. 1 Of the state of the mirror with regard to the foci. 2 Of Lateral faults. 3 Of Lunar appearances. Blotches. Heatspots. 4 Of concentric circles. 5 Of scattered light. 6 Of Dim Polish or Cloudiness. 7 Of Scabrousness, Varnish, & Crystallizations. Section XXXI Of the incidental imperfections of mirrors. 1 Of unequal polish. 2 Of concentric circles. 3 Of defective inside polish. 4 Of defective outside polish. 5 Of Lateral faults. 6 The stroke not having its effect. 7 Of Bars. 8 Of Pores and crystallizations. 9 Of adhering pitch. 10 Of Blotches, Lunar appearances and Heatspots. 11 Of Stains. 12 Of Scabrousness. 13 Of Varnish. 14 Of Dim polish. 15 Of Cloudiness and motled appearances. 16 Of Scattered light. 17 Of Temperature in fault. 18 The structure of the polisher in fault. 19 The construction of the mirror in fault. 20 The polishing apparatus in fault. 21 The last resource. Section XXXII Of th critical examination of mirrors. 1 Remarks on the examination of mirrors. 2 Examination of the figure. 3 Examination of the distinctness. 4 Examination of the polish. Section XXXIII Giving figure to mirrors. 1 Remarks on giving figure. 2 To lengthen the inside focus when too short. 3 To shorten the inside focus when too long. 4 To lengthen the middle rim when too short. 5 To preserve the middle rim. 6 To shorten the middle rim when too long. 7 To lengthen the outside focus when too short. 8 To shorten the outside focus when too long. 9 Of the figures of the Conic Sections. 10 Recapitulation. Section XXXIV Of plain mirrors for Newtonian telescopes. 1 Preparation for giving figure to plain mirrors. 2 Trial of the figure of plain mirrors. 3 To take off convexity. 4 To take off concavity. 5 Object mirrors for Gregorian. 6 Small mirrors for Gregorian. Section XXXV Of the distinctness of mirrors. 1 Of distinctness in the stroke. 2 Of distinctness by Round motions. 3 Of distinctness by side motion. 4 Of distinctness by Gutters. 5 Of distinctness by various means. Section XXXVI Of high polish. 1 Of polishers that will give a bright polish. 2 Sharp polishers give gloss. 3 Of the length of time for high polish. 4 Of water polish. Section XXXVII Of finishing the work of polishing. 1 Of taking the mirror off the polisher. Section XXXVIII Of cleaning and preserving mirrors. 1 Of cleaning tarnished mirrors 2 Of preserving mirrors. Section XXXIX Of the adjustment of mirrors. 1 Remarks on the adjustment of mirrors. 2 Of adjusting the mirror. Section XL Selection of successful experiments. 1 7 feet mirrors. 2 10 feet mirrors. 3 14 feet mirrors. 4 20 feet mirrors. 5 Large 10 feet mirrors. 6 25 feet mirrors. 7 40 feet mirrors. 8 Plain mirrors. 9 Gregorian and other Mirrors Appendix II Translation of Della Torre letter cvi QUARTZ SPHERULES AS MICROSCOPES Della Torre's Method of making crystal globules to be used instead of lenses for single Microscopes. Translated from the italian Scelta di Opusculi. Read Feb 9. 1781. THREE things are required to make little globules of Crystal for single Microscopes. A pair of small perpetual Bellows. Some good Tripoli. And some solid Cylinders of Crystal of different thicknesses. The bellows must move easily and be kept full so as to blow the flame equally, thro' a little pipe, against the cristal. The point of the pipe must enter a little way into the lower part of the flame, and its diameter should be a line. Care must be taken not to melt it. The blast of the flame should be directed horizontally and the flame will be found to consist of two different parts. Two thirds from the base of it are white, from thence to the point is transparent and without colour. With this latter part the cristal is to be melted. There is no danger of smoking the cristal in this part of the flame, which, on the contrary soon happens when the white part of the flame is touched. The crystal must be well cleaned before it is exposed to the flame and never touched with the finger. Paper is the best for cleaning the cristal. or any part of the apparatus. The tripoli should be in a piece of 4 or 5 inches long and 4 broad ; and made smooth on one part. The best Tripoli is whitish of a fine grain and heavy; and which after calcination turns reddish. To calcine the tripoli put it in the midst of charcoal not much set on fire and let it remain there till all the charcoal has taken fire, is burnt out and extinguished of itself. When all is cold take out the tripoli, which is calcined and fit for use. On the smoothed side of the Tripoli make several little holes of various sizes, in which the globules are to be placed. Take care not to touch them with your fingers. If it wants cleaning let it be done with paper. The Crystal should be round; for, if square the globules will be apt to be smoked. The thickness of the Cylinders of Crystal should be different such as half a line, a line &c: Having all this ready the work is as follows. Take two Cylinders ; put them into the flame, end to end; when they begin to melt draw them out (holding one in each hand,) to as fine a thread as you please and separate them in the fire. Put by one of them. Hold the extremity of the other in the point of the flame and it will run up into a semiglobular form, which may be made as large as you please. These semi-globules must be broke or cut off and put by in papers. When you have a sufficient number of them place them into the little holes of the Tripoli. Blow the flame, not against them (for they would be blown away) but against the tripoh which will soon be red hot. Go on in that manner till the little globules are of a white heat. Then they are finished. Take them out of the fire to cool. When you want to make large globules, it will be well to shake the tripoli a little that the globules may the better assume a spherical form. But this must be left to experience which soon will teach many little circumstances that can not so well be described. In this manner globules have been made that magnified from 42 times up to 1280. 1920. 2560. 3840. 5120. 10240 times. Appendix III Unpublished paper on specula construction (pg cviii-cvix, Dreyer, 1912) On polishing Specula by a Machine* (1789) About six years ago, I made various attempts to polish Mirrors for telescopes by a machine ; but after many trials, with Specula of ten feet focal length, and nine inches diameter, I found that notwithstanding I had provided the same kind of movements in my apparatus, which I generally used to give by hand, the figure of a Speculum always suffered under the operation. So far indeed was the machine from giving a proper shape to the mirror, that it came out deformed, notwithstanding I had compleatly figured, and polished it before I placed it on the machine. † This bad success made me lay aside all thoughts of any further attempt ; and had it not been for the particular situation in which I found myself last summer, when I was obliged to employ twenty men to polish my second forty feet Speculum, I might perhaps never have made another trial to do such work by mechanical powers. The idea of a machine however was now again as it were forced upon me ; when I considered, that all the essential part, I had formerly taken in the construction of a Speculum, was fairly excluded in the present operation. The enormous weight, of about five and twenty hundred pounds, to be moved upon the polisher, would not permit the use of those delicate touches of the hand, by which I had been accustomed to form small mirrors ; and I found myself reduced to the situation of merely directing the unwieldy manoeuvres of a set of men, who when they did their best, could only act like a very imperfect machine. As soon as I perceived that I was, in fact, already working with a machine, there wanted not much to convince me that twenty men made a very bad one ; and that I should find no manner of difficulty in contriving another, that would do the work much more to my satisfaction. This point being brought home to me with such forcible arguments, I caused all my apparatus for polishing with the twenty-men-machine to be pulled to pieces that I might never be tempted to use it again ; and began now to consult the very compleat theory of polishing, which long experience had furnished me with. I perceived at once the error of my former mechanical constructions, and could explain the cause of my disappointment six years ago. A few days sufficed to plan an apparatus ; and having got it executed, of such a size as would polish a Speculum for my 20 feet telescope, I began to work one of the mirrors with it, by way of trying the performance of the machine. A few hours pointed out what still was wanting ; and when such little defects, as appeared to require an alteration, were corrected, I found myself in a condition to begin a series of experiments, on the effects of working mirrors mechanically. My former principles, of certain strokes having certain effects, upon the figure of a Speculum, were now very strictly re-examined ; that I might see whether every mode of operation would have the same result, when a machine was used. Most of the rules I had laid down were confirmed ; one way of working however proved to be of a different import * [Sent to the Royal Society, but apparently not read at a meeting. - Ed.] † [These experiments are not mentioned in the Polishing Record. - Ed.] from what had been ascribed to it ; but this I could easily explain. For, in the first place, the considerable heat of the hand, which is always of a much higher temperature than the place, and materials which are employed in the work, was now removed ; and, next to this, I comprehended very well, that experiments made with a machine, which for any given time will truely perform a certain stroke, with mechanical accuracy, must be more conclusive, than when the same operation is executed by hands, which it is not so easy, nor perhaps possible, to direct, for an hour or two together, without some considerable deviations from the proposed movements. These experiments had taken me up about five weeks. At last, by the 14th of February, I had not only settled my plan of working, but had prepared everything requisite for the purpose ; and that now my trial might be decisive, I totally destroyed the figure and polish of one of my 20 feet Specula, before I laid it on the machine ; so that, besides lateral defects, the focus of the outside rays was above an inch shorter than that of the inside. In this condition I set the machine to work. The day was pretty far advanced when we began ; but as my share of the business was only to feed the machine from time to time with polishing stuff, I could now had the advantage of making it continue the work without interruption, while the usual calls, of supplying our own machines with necessary refreshments, took me away from the polishing apparatus. A little before nine in the evening I took off the Speculum, with an intention to proceed next day ; but on examination it appeared, that, in little more than 8 hours, the Speculum had acquired a most beautiful, glossy polish ; and this occasioned an alteration of my design, which now was to expose the Speculum to optical trials. By a day object, of some letters, fixed up at a convenient distance, I found that there was no dispersion of rays. I could read them with more facility than with the best of my 20 feet mirrors, which hitherto I had preserved with the greatest care. It is remarkable that this machine-polished Speculum, which now excelled the former, had frustrated my endeavours for near two years past ; in which time I could never succeed to make it perform like the other. This failure I used to ascribe to certain cristallizations, that have taken place in cooling, when the metal was cast ; and which indeed are very detrimental to Specula, from a difference in the grain, if I may so call it, which is occasioned by them. When I directed the telescope to celestial objects, I was still more convinced of the perfection of this new mirror. The small stars were all brought to so precise a focus that their light was gathered into a point ; and I saw the satellites of the Georgian planet with greater ease than I could ever see them before. Thus it appears that we have now obtained an addition to our mechanisms, which certainly must be valuable, as it will secure to us the perfection of astronomical telescopes, by reducing the art of making Specula for them to a certainty. An apparatus for polishing a forty feet Speculum is nearly finished, and by some trials I have already made, I find that its construction will conveniently answer all the movements I require. The simplicity of the machine, indeed, is such, that there can hardly be any difficulty in its performance. Slough near Windsor, March 4th 1789. Appendix IV Biographies (excluding music-oriented, juvenile and non-English works; compiled from WorldCat) Biographical account of Sir William Herschel 1823, English Book : Microform p. [209]-226 ; 22 cm. Edinburgh : Printed for A. Constable William Herschel F Arago 1980, 1857 New ed. English Book p. [167]-195 ; 21 cm. [Sidcup, Kent, England : P.M.E. Erwood], ISBN: 090732200X by François Arago ; reprinted from Biographies of distinguished scientific men ; translated by W.H. Smyth, Rev. Baden Powell and Robert Grant Herschel. F Arago, 1871, English, Smithsonian institution. Annual report. 1870. Washington, 1871. 24 cm. p. [197]- 222. Chronological table of the memoirs of William Herschel: p. 201-204. A synopsis of the scientific writings of Sir William Herschel. Author(s): Holden, Edward Singleton, 1846-1914; Hastings, Charles S.; 1849-1932,; (Charles Sheldon),; joint author. Year: 1881 In: Smithsonian institution. Annual report. Washington, 1881. 1880. 24 cm. p. 509-622 Sir William Herschel his life and works Edward Singleton Holden, 1881, English Book : Microform vii, 238 p. : ill., New York : C. Scribner's Sons, "Bibliography. I. List of the published writings of William Herschel on astronomical subjects. II. List of works relating to the life and writings of William Herschel. III. List of the published portraits of William Herschel": p. 215-233. The Herschels and modern astronomy. Agnes M Clerke, 1895, English Book 224 p. front. (port.) 19 cm., New York, Macmillan, Sir William Herschel, 1738-1822, biographical study. John Ebenezer Bryant, 1800-1899?, English Book 99-125 p. illus., ports. 21 cm.,[n.p., from The world's great scientists Chapter V.] William Herschel and his work James Sime, 1900, English Book vii, 265 p. 19 cm., New York, C. Scribner's sons, [Sir William Herschel, biographical materials] English Archival Material 1 folder. In: Kremers Reference Files A short account of Sir William Herschel's life and work, chiefly from unpublished sources J L E Dreyer, 1912, English Book lxiv p. 31 cm. [n.p.] Herschel Hector Macpherson, 1919, English Book 78 p. front. (port.) 19 cm. London, New York, Society for Promoting Christian Knowledge; The Macmillan Company, Sir William Herschel. W H Stevenson, 1924-1925, English Book 238 p. [i.e. 42 p.] : ill. London : Optical Society, Transactions of the Optical Society ;; v.xxvi, no. 4; The Herschel chronicle; the life-story of William Herschel and his sister, Caroline Herschel Constance A Lubbock, 1933, English Book x p., 1 l., 388 p. front., illus. (music) plates, ports. 25 cm. New York, Cambridge, Eng., The Macmillan company; The University press, The Herschel effect Delia Taylor Sinkov, 1936, English Book : Thesis/dissertation/manuscript 78, iii leaves : ill. ; 28 cm. Typescript./ Includes bibliographical references (leaves i-iii)./ Dissertation: Thesis (M.A.)--Smith College, Northampton, Mass., 1936. Sir William Herschel 1738-1822 Frederick E Brasch, 1939, English Book 7 p. ; 25 cm., [Northfield, Minn. : s.n., Cover title./ "Reprinted from Popular astronomy, vol. XLVII, no. 2, February, 1939." William Herschel, explorer of the heavens. J B Sidgwick, 1953 , English Book 228 p. illus. 21 cm., London, Faber and Faber A collection of manuscripts, printed books and pamphlets, scientific periodicals, scientific apparatus, portraits and memorabilia of the Hershel family ... now the property of Mrs. E.D. Shorland ... E D Shorland, 1958, English Book 57-94 p. illus. 25 cm., [London, Sotheby] William Herschel. A Armitage, 1963, (c)1962 [1st American ed.], English Book 158 p. illus. 21 cm., Garden City, N.Y., Doubleday, William Herschel and the construction of the heavens. Michael A Hoskin, 1964, (c)1963 [1st American ed.], English Book 199 p. illus. 22 cm., New York, Norton The king's astronomer, William Herschel. Deborah Crawford, 1968, English Book : Juvenile audience 191 p. 22 cm., New York, J. Messner William Herschel : pioneer of modern stellar astronomy Carol Linn Miller, 1975, English Book iv, 98 leaves : ill. ; 29 cm. [New Orleans], Bibliography: leaves 93-98./ Dissertation: Thesis (B.A.)--Tulane University, May 1975. William Herschel, astronomer and musician of 19 New King Street, Bath Patrick Moore, 1981, English Book vii, 26 p., [14] p. of plates : ill., facsims., ports. ; 22 cm. Sidcup, Kent, England : P.M.E. Erwood in association with The William Herschel Society, Bath, England, ISBN: 0907322069 ----------------------- Little journeys to homes of great scientists : Herschel Elbert Hubbard, 1905, English Book p. 129-155 : port. ; 21 cm., East Aurora, N.Y. : The Roycrofters, -------------------------------- Herschel at the Cape; Diaries and correspondence of Sir John Herschel, 1834-1838. John F W Herschel, Sir; David Stanley Evans, 1969, English Book xxxv, 398 p. illus., facsims., maps, ports. 24 cm., Austin, University of Texas Press ISBN: 0292783876 The shadow of the telescope; a biography of John Herschel. Günther Buttmann; David Stanley Evans, 1970, English Book xiv, 219 p. illus., facsim., ports. 24 cm. New York, Scribner A calendar of the correspondence of Sir John Herschel Michael J Crowe; David R Dyck; James J Kevin, 1998, English Book 828 p. ; 28 cm., Cambridge ; New York : Cambridge University Press, ISBN: 0521631491 Letters and papers of Sir John Herschel : a guide to the manuscripts and microfilm Michael J Crowe; Paul Kesaris, 1990, English Book xxxviii, 248 p. ; 28 cm., Bethesda, MD : University Publications of America, ISBN: 1556552181 Book Review: The catalogue of the Herschel Library Troy, 2001 Book Authors: Herschel, I.; Ross, Sydney Journal: Journal for the history of astronomy, vol. 33, no. 1, p. 88 (2002)[B] See accompanying bibiliography for a list of Herschel-related works. Not all of these have been consulted in the preparation of this paper. "Amateur telescope making," 1928, edited by Albert Ingalls, page 257 "The Life and Scientific Papers of Sir William Herschel," 1912, Dreyer, J. L. E. "The Telescopes of William Herschel," Journal of the History of Astronomy, 1978, Bennett, J. A. Ibid., Bennett, p. 107, footnote 186 RAS MSS Herschel W. "Catalog of the Papers and Manuscripts of the Royal Astronomical Society", 1978, Mem. RAS, Bennet, J. A. Article 5, Section 5 - Of the composition of metals , "On the Construction of Specula", RAS MSS Herschel W. 5/13 Article 2, Section 37 - Necessaray examination of the work, "On the Construction of Specula", RAS MSS Herschel W. 5/13 "A Calender of the Correspondence of J. F. W. Herschel," XXX, Cambridge, Crowe, Prof. Michael