The following messages form part of a wider ranging discussion on the Yahoo Microscope group during February 2004. Discussion point was the (im)possibility of seeing fine diatom details with objective lenses that theoretically do not permit seeing such fine details.  Already by 1860 diatom structures had been described that were below the resolution limit of the (dry) optics available at the time; my interest in this was whether water or oil immersion lenses could have been used for these observations, as immersion can increase aperture to a higher level then possible with dry objectives (and hence can achieve higher resolution).    Mervyn Hobden and James Solliday described the development of the high NA lenses, culminating in the famous 1/10” Tolles lens, which even by today’s optical standards is hard to beat. This objective closed a notorious discussion between two schools of microscopists about whether immersion of the lens with water or oil could indeed increase resolution by having a larger aperture then a dry objective. This discussion became known as ‘the battle of the apertures’.  Many thanks to Merv and James for their time in this fruitful discussion and to Aubrey Scoon for the ‘impossible’ image of Frustulia rhomboides.  The archives of the Yahoo Microscope group can be reached at http://groups.yahoo.com/group/Microscope/

Image courtesy of Aubrey Scoon, used with permission. Frustulia rhomboides, the striae lines ca 300 µm apart. Image taken with a 0.8NA objective lens, which theoretically only permits details more then 380 µm apart to be resolved.  Message 14525  From:  "ascoonuk" <ascoon@p...>  Date:  Sat Feb 14, 2004  4:43 pm  Subject:  Diatom Pic   Hello All,  I've just uploaded some diatom pics to my briefcase, they are in th  folder called "High Res". The briefcase link is:  http://uk.f2.pg.briefcase.yahoo.com/ascoonu   There are 3 images of Frustulia rhomboides, the slide is a Kemp Tes  slide (the 8 form one).  What is interesting about these is the setup used to take the pics.  They were taken on my Zeiss (Jena) Epival, using a Jena 0.9NA turre  phase condenser (in the passthrough position, no annuli), upper len  set about 8mm below the slide, and a 50X 0.8 NA metallurgica  objective. The light is a combination of normal light passed straigh  through and a slightly oblique element mainly in the green band via   Risley prism (approx 7.5 degrees off axis). The objective was use  dry, and the tube length was extended to push up the magnification.  Pictures were taken with my little Logitech webcam, which as you wil  all note, needs some cleaning! :-)  The exact objective markings are Planachromat 50x/0,80 oo/0-C Th  "oo" is the nearest I can get to an infinity sign!.  Unless I am seriously mistaken, the lines of F. rhomboides ar  typically around 300nm apart. According to the Abbe formula thes  pics are impossible, they are even impossible using the much mor  liberal Nelson formula. Please work it out for yourselves.  I can't resolve Amphipleura pellucida with this setup (yet), but it'  extremely tricky to get even the pics that I did. The slightes  change in the Risley angle or lateral position throws it ou  completely. I moved the prism after taking these pics and now I can'  even get it back! It was more luck than design that I managed to ge  these. But I think it illustrates the point that under certai  special conditions, much more is possible in practice than mere theor  allows.  Anyone suffering from paradigm angst is strongly advised to turn awa  now, breathe deeply into a paper bag and keep repeating, "It's just a  artifact, it's just an artifact...."! :-)  Best wishe   Aubre   Message 14542  From:  "mervhob" <heather.hobden@n...>  Date:  Sat Feb 14, 2004  10:15 pm  Subject:  Re: Diatom Pic    Dear Aubrey,  No, they are no artifact, nor do they break any laws of physics. The  stria on Rhomboides are, according to my 1862 copy  of 'Carpenter',vary between 111 - 60 stria in 1/1000 inch. This  translates to 228nm - 300nm. Just a minute, 1862? - that is long  before Abbe and homogeneous immersion! Ere, and the cheeky soul also  claims to have resolved Amphipleura pellucida - 130 - 120 stria per  1/1000 inch! Well, that is under 200nm. And with an NA that could not  be greater than 0.95. The conspiracy theorists in this group will now  propose that Sollitt, who made these measurements, invented a time  machine, nipped into the future and purchased a good Leitz/Zeiss NA  1.4 APO on ebay for his Powell and Lealand No. 1...... There is  alas, no mystery. Diatoms are three dimensional objects composed of  refractive material. The Abbe/Foucault limits only apply to the exact  conditions specified - two dimensional periodic array,infinitely  sharp transition, Fraunhofer illumination. However, the array does  not suddenly disappear for 1nm under the specified limit, the  perception gradually fades, the limiting perception is stated by  Francon as 0.08lamda/2nsinu. So, under the correct illumination  conditions, the perception of the stria is eminently feasible - as  you have demonstrated. Well done Aubrey! As I pointed out in an  earlier posting, it all hinges on what you mean by 'resolved'. We do  not 'resolve' the dots on Amphipleura pellucida - we perceive them as  a regular modulation of the interference diffraction pattern. This  will be dependent on the wavelength of the interfering light - if you  vary the wavelength, the pattern will fade and disappear. This I have  observed, using a monochronometer on Amphipleura pellucida, and  oblique illumination. Now this has all been stated, I daresay some  mathematician will crunch through the algebra, and get a Nobel Prize  for it. Some people might like to write out 1000 times - 'I must not  use the Abbe limits without understanding them.'  Very Best Regards - and that incudes everyone in this marvellous  group,  Mer    Message 14558  From:  "rvanwezel" <renevanwezel@h...>  Date:  Sun Feb 15, 2004  1:27 pm  Subject:  Re: Diatom Pic    Merv, please some more data: When was the first water immersion build, and by whom? Was this befor  oil immersion? I remember you mentioning 3 great builders, P&L, Tolles and Hartnack. You mentioned Hartnack together with the dat  1850's, but wasn't that a bit early?  Thanks, Ren     Message 14592  From:  "mervhob" <heather.hobden@n...>  Date:  Mon Feb 16, 2004  12:01 a  Subject:  Re: Rene request for Data -Diatom Pic     Rene,  Quoting E.M. Nelson, 1900, the first water immersion was brought t  London in 1855 by Prof. Amici. However, its aperture was no greate  than that of the high drys of the time - the P&L 1/16" had an NA o  0.99(175deg). This was followed by water immersions by Hartnack i  1862 - these were stated to be inferior to the P&L 1/25" dry with a  NA very close to 1.0(!). This could resolve Norbert's 15th band, 90,078 lpi, or 281nm. In 1869 P&L produced their first W.I. objective, 1/16" which Col. Woodward used to resolve the 19th band, 112597 lpi, or 225nm. This was beaten in 1872 by Tolles W.I. with   duplex front, which Woodward said beat all other objectives that h  had in his collection. The higher aperture W.I. objectives did no  start to appear until the 1870s, as it began to be appreciated, du  to Tolles, that the working aperture could be improved by this means. This started the infamous 'Battle of the Apertures', in which Wenha  refused to accept that improvement was possible. So it is extremely unlikely that Sollit and Harrison used a W.I. i  1862, in fact, we know that they did not - Carpenter states, regarding the ability to see stria on Amphipleura pellucida, and th  doubts that had been expressed by Hendry and others, he himself i  convinced, 'having himself seen regular, distinct, and unmistakabl  stria in this Diatom - through the kindness of Mr. Lobb who has show  him this object with a 1/8" objective on Messrs Powell and Lealand'  large microscope with an achromatic condenser of 170deg.' I a  inclined to take Carpenter's word for this - as my friend Ted Brai  points out - 'Well, they just didn't know any better!'  Cheers, Mer     Message 14599   From:  James Solliday <oldscope@y...>  Date:  Mon Feb 16, 2004  6:28 a  Subject:  History of the Immersion objective: Ji   All you every wanted to know about Immersion Objectives.  The story actually starts quite early when in 1678, Hooke gave his presentation, "Lectures and Collections" which was published that same year in hi  "Microscopium". Hooke was the first to suggest the technique of Immersion. H  writes: "that if you would have a microscope with one single refraction, an  consequently capable of the greatest clearness and brightness, spread a littl  of the fluid to be examined on a glass plate, bring this under one of th  globules, and then move it gently upward till the fluid touches and adheres t  the globule". By 1812, Sir D. Brewster suggested immersion of the objectiv  into the liquid medium. Amazingly about that same time Amici began addressin  the problem of chromatic aberration (Woodruff, 1939).  By 1840, the first immersion lenses were made by Pro. Amici. According t  Mayall they were designed to be used with oils having the same refraction a  glass, homogeneous-immersion (Mayall, pp.1119) (The Northern Microscopist, Vol.2, 82/307). This was not done with the conception of increasing th  apertures that revelation was left to Tolles. Amici's work was intended to ge  more correction of the aberrations. However, the use of oil on expensive slide  was not readily accepted by the public, Amici gave up the oil system and adopte  water as the immersion fluid (Mayall, pp.1119). In 1853, Prof. Amici of Moden  constructed his first water immersion objective (W.G, Hartley, 1993). At th  1855 Paris Exposition, Amici introduced his water immersion objective. Nache  Sr. and Hartnack were inspired to work out systems of their own (Mayall).  By 1858, Tolles made his first immersion objectives, with water, which had tw  frontals. Tolles constructed objectives with two exchangeable front elements, one for dry work and the other for water immersion (Three American Microscop  Builders, pp.38). In a meeting of the Boston Society of Natural History (1867), Charles Stodder demonstrated a Tolles 1/10th objective, both dry and we  (Warner, 1997). In August 1873, he made his famous homog. immersion 1/10t  (AMMJ,1884, pp.168).  In 1859, Edmund Hartnack first exhibited his water immersion objectives (W.G, Hartley, 1993, pp.36/328). He also added the correction collar to th  water-immersion lens for the first time. Hartnack sold 400 of these lenses ove  the course of the next five years.  By 1860, the following makers were producing (water) immersion objectives. Nachet, Bruno Hasert in Eisenach (said to be as good as Hartnack's), C. Kellne  in Wetzlar, G&S Merz of Munich, Friedrich Adolph Nobert in Pomerania and Hug  Schroder In Hamburg. In that same year, Pieter Harting compared a P&L 1/25t  dry objective with Hartnack's most powerful (water) immersion lens and found i  favor of the P&L. In 1862, Hartnack displayed his immersion objectives at th  London, International Exhibition. That same year Prazmowski joined Hartnac  (Paris), together they made substantial progress in the water immersio  objectives, thanks to Prazmowski's combination of theory and practical skills. The result was that by the 1867 PARIS exposition, Hartnack's lenses were judge  the best (Mayall, pp.1119). Prazmowski was the former director of th  Observatory of Warsaw (Varsovie). In 1877 he continued the business of Mr. Hartnack (Paris) who had been the successor to the celebrated factor  of Oberhaeuser (Trutat, Traité Élémentaire du Microscope 1883, pp.131).  In 1864, Pro. Hamilton L. Smith reported that "Messrs. Wales & Co. intend t  supply with their higher objectives an extra front for immersion in water", thi  was a reference to William Wales. His best known objective was a 1/30th inc  made for the Army Medical Museum that Woodward used later to photograp  Amphipleura pellucida (RMS, June,1964, pp.125).  In 1865, Powell & Lealand were the first in England to make a water immersio  lens (W. Hartley, 1993, pp.31/36). Beale said that Powell made for him a 1/25" immersion after the lead of Hartnack. See 1869. On Oct. 15th, 1865, Powel  delivered a 1/50" immersion objective to Lionel S. Beale (W.G. Hartley, 1993, pp.31). In 1868 Powell undertook additional experiments with immersion system  after Mayall showed him examples (objectives) produced by Hartnack (Mayall, pp.1119). By 1869 Powell's immersion lenses were considered the best in th  field. He had made a few tenuous immersion lenses for Beale in 1865, which wa  some time before he offered them to the general public.  In 1867, Gundlach showed his new glycerin immersion objectives at the Expositio  Universelle, Paris (1867), claiming "the first instance of the intentiona  construction of objectives for use with an immersion fluid of higher refractiv  index than water"(RMS, June,1964/124). Also at the 1867 PARIS Exposition, Hartnack exhibited his improved water immersion objectives (Mayall). Th  exhibit of Hartnack & Prazmowski surpassed all other entries for his ne  immersion lenses. That year, Hartnack produced a water-immersion objective o  1/12th inch (No.9) & 1/21inch (No.12).  In 1867, Tolles made immersion lenses for glycerin as well, the 1/16th inc  immersion which resolved Nobert's 19th band, possibly for the first time. Witnesses: Mr. R. C. Greenleaf and C. Stodder, Boston (AMMJ,1893, pp.303).  By 1870, Thomas Ross (at the suggestion of H. Van Heurck) began making wate  immersion objectives. His 1/12th was well received but very expensive.  In 1871, Tolles demonstrated his homogeneous immersion objective using Canad  balsam as a medium. At the death of Mr. Tolles the editor of The Microscope, Mr. Stowell received an account of the life of Tolles from Mr. C. Stodder, Boston, Tolles business partner. Concerning the Tolles homogeneous objective  he records, "This he demonstrated in 1871, but owing to the fact that at tha  time Canada balsam was the only fluid known to possess the same refractive inde  as crown glass, his discovery remained useless until 1877, when Prof. Abb  discovered a fluid which was practical for such a purpose." (The Microscope, 1884, No.1, pp.5). However, attention was afforded Mr. Tolles on this concep  in 1873, with the production of his 1/10th immersion. In 1871, A public debat  began between Tolles and Wenham over the question of the aperture of immersio  objectives. The debate actually began with a disagreement between Dr. Pigot  and Wenham, drawing Tolles in with a challenge put out b  Wenham.  Hartley says that in 1871, Zeiss produced their first water immersion objective. However, it is certain that in 1872, Zeiss introduced Abbe's water-immersio  objectives. The Zeiss catalogue offered 3 water immersion objectives, al  claiming an angular aperture of 180º. Described as follows: a 3mm, a 1.7mm an  a 1mm, all with an N.A. of 1.0. The No.3 (1.mm) came with a correction collar.   In August of 1873, Robert Tolles made a 1/10th inch objective for homogeneou  immersion in Balsam, having an aperture of 110 degrees or 1.25 n.a. (Thre  American Microscope Builders, 1945)(AMMJ, 1884, pp.168) and being a three-syste  lens. This represents the first publicly recognized true homogeneous immersio  system for the microscope (Bradbury, 1969) (JQMC, V.32, pp.294). The same mont  he made his first lens of the duplex front formula, a 1/5th glycerin immersio  of 110° balsam angle (n.a. 1.27) (TAMB/38). Both passed into the possession o  the Army Medical Museum at Washington, both used in softened balsam (AMMJ,1884, pp.168). In 1874 his formula and objective were sent to England for inspectio  and submission in the Journal of the RMS. Earlier in 1873 he also made hi  1/5th at N.A. 1.27 (duplex glycerine) and 1/10th at N.A. 1.27 (TAMB/38). Thi  was partly in response to Wenham's denial of the ability of immersion to effec  an angular aperture greater then 180° in ai  (RMS, June,1964, pp.120).  Finally, by August of 1877, Zeiss produced Abbe's oil immersion objectives, which became known as "homogeneous" immersion (Innovation, No.1, 1996). Mayal  says the date was 1878. However, a bit latter in 1879, Abbe published his pape  on Methods for Improving Spherical Correction in the RMS Journal (June). H  describes the fluid lenses used in his experiments (1873). He also states tha  " homogeneous immersion system admits of a useful increase of aperture closel  approaching the ultimate limit which is imposed by the optical qualities of th  materials available" (RMS,1879, pp.824). As for the use to which these ne  objective were applied, in 1882, Dr. Robert Koch described tuberculosi  (tubercle bacillus). He used a Zeiss oil objectives & Abbe's condenser. Koc  met with Abbe and suggested that he develop an achromatic condenser for use i  photomicrography. In 1904 the firm of Zeiss presented Dr. Koch with thei  10,000th homogeneous 1/12 oil immersion objective. Koch ha  enthusiastically attributed part of his success to the immersion lenses of Abb  (Zeiss) (Innovation, No.1, 96).  Sincerely, Jim Solliday (MSSC).   Message 15142  From:  James Solliday <oldscope@y...>  Date:  Sun Feb 29, 2004  6:39 am  Subject:  The Aperture Wars, from Ji   Dear Rene: Enclosed is a brief history of the aperture wars, a big part of the developmen  of the Immersion objective... Ji   The Aperture War  Research and notes by Jim Sollida   In 1871, a public debate began between Tolles and Wenham over the question o  the aperture of immersion objectives. The debate actually began with   disagreement between Dr. Pigott and Wenham, drawing Tolles in with a challeng  put out by Wenham. The following quote is by Mr. Wenham, "I challenge Dr. Pigott, or anyone, to get, through the object-glass with the immersion front,   greater angle, or any portion of the extraneous rays that would in the othe  case be totally reflected, as no object-glass can collect image-forming ray  beyond this limit" (The Monthly Microscopical Journal, V, 1871, pp.118). Muc  of the early debate centered on a 1/10th and a 1/5th made by Tolles. Eventually, Tolles sent a 1/6th inch lens to Mr. Frank Crisp having an extr  front lens intended for immersion (Mayall, Cantor Lectures (1886-88), pp.1119). This famous lens was the subject of a great deal of correspondence lasting fro  1874-1878. In 1878 Professor Keith computed the angular aperture of th  1/6th finding it to be of 110 degrees (RMS, 1878, pp.142). This evidenc  finally settled the debate and completely vindicated Mr. Tolles. In America th  debate was known as "the war of the apertures." Throughout the debate, Mr. Tolles was assisted by Dr. J.J. Woodward of Washington D.C., and by Prof. Keit  of Georgetown (H. Smith, pref.) (Also see, RMS, June 1964, pp.120).  A few events in the productive life of Tolles may help add reference to th  development of the homogeneous objective. In August of 1873, Robert Tolles mad  a 1/10th inch objective for homogeneous immersion in Balsam, having an apertur  of 110 degrees or 1.25 N.A. (Three American Microscope Builders, pp.38)(America  Monthly Microscopical Journal, 1884, pp.168) and being a three system lens. This represents the first true homogeneous immersion system for the microscop  (Bradbury, 1969, pp.245) (LM/36/39) (Journal of the Quekett Microscopical Club, V.32, pp.294). The same month he made his first lens of the duplex fron  formula, a 1/5th glycerin immersion of 110° balsam angle (n.a. 1.27) (TAMB/38). Both passed into the possession of the Army Medical Museum at Washington, bot  were intended for use in softened balsam (AMMJ, 1884, pp.168). In 1874 hi  formula and objective were sent to England for inspection and submission in th  Journal of the RMS. This was partly in response t  Wenham's denial of the ability of immersion to affect an angular apertur  greater then 180° in air (RMS, June, 1964/120).  In 1874, Tolles requested Dr. J. Edward Smith of Cleveland, to report on a 1/6t  duplex of 180°. Dr. Smith confirmed the new lenses excelled all other  including higher magnifications such as the 1/15th. He then received a Tolle  1/10th "duplex" which was judged even better. Latter that year (1874) Dr. Smit  received a 1/10th from Mr. Herbert Spencer (different formula then the Tolles), "the performance of which is not excelled by any glass yet made, be it a fift  or a fiftieth". There is some doubt if Dr. Smith was using the Tolles in balsa  as intended. Tolles was to have added an emulsion agent to Canada Balsam tha  inhibited its normal drying time.  Also in 1873, Tolles designed an instrument for measuring the aperture of hi  objectives. He described it as "An apparatus for obtaining the balsam angle o  any objective" (The Monthly Microscopical Journal, 1873, pp.212). In 1874, Mr. R. Keith published in the Monthly Microscopical Journal, proof of the expande  aperture of the Tolles 1/10" objective. Tolles had described his 1/10th in Nov. 1873 along with its aperture. The significance of this debate was the fact tha  an immersion objective could have a greater aperture than corresponds to th  maximum possible for a dry lens. With Tolles objectives the front lens wa  immersed in balsam having a similar refractive index as the front element, thu  establishing a homogeneous system (Mayall, pp.1119). Tolles distinctl  understood the influence of the use of higher refractive media. By performin  tests, Dr. J.J. Woodward confirmed that "the definition unmistakably better tha  with water immersion" (MMJ, XII, 1874, pp.127). Bot  Professor Keith and Dr. J.J. Woodward gave a detailed computation of ray path  through the Tolles balsam immersion 1/10th inch (RMS, June, 1964, pp.120). Th  Zeiss oil-immersion lenses were not issued until 1878 (Mayall). As for wh  first developed the "homogeneous-immersion formula" with the intention o  increasing aperture, Mayall says, "Mr. R.B. Tolles stands alone as the inventor" (Mayall, Cantor Lectures (1886-88), Royal Society of Arts.).  As mentioned above, in addition to Dr. J. Edward Smith inspecting the Tolle  1/6th immersion, it was sent to England in 1874 and used to persuade the Societ  in the debate with Wenham over the limits of aperture. The objective was owne  by Frank Crisp and mentioned in the RMS Journal of 1874. In 1878 Professo  Keith computed the angular aperture of the 1/6th finding it to be of 110 degree  (RMS, 1878, pp.142). This evidence along with the endorsement of Prof. Stoke  (an English physicist) finally settled the debate (Three American Microscop  Builders, pub. by American Optical Company (1945).  In 1879, John Mayall, wrote that he tested the best objectives available. H  compared the Tolles 1/4th and 1/8th against the best lenses "by English, French, and German opticians," including immersion objectives by the most renowne  makers in Europe. He concluded that, "without reserve of any kind, I say thes  lenses (Tolles) are the finest I have ever seen." It was also said at the time, "I find, on the most severe test, there is in Tolles' lenses a better correctio  for spherical aberration" (How to See with The Microscope; 1885, edition, by J. Edwards Smith, pp.11). The reputation of Tolles was by now so respected that i  let Dr. J. Edward Smith to say of Tolles, "who with almost superhuman genius an  energy grapples with the very laws of optics, and bends them to his inflexibl  will" (H. Smith, 1880).  Robert Tolles died on Nov 17, 1883 in Massachusetts hospital, Boston. After hi  death, Charles X. Dalton took charge of Boston Opt. Works (1883-95). He wa  known to continue making microscopes but with his signatures hidden. Dalton wa  a workman for Tolles doing his brass work (RMS, June, 1964, pp.124).  Even though Robert Tolles prevailed in the Aperture Wars, his rival Wenham wa  no slouch. It is only fair that a few good words be said of him and hi  considerable contributions to microscopy. Francis Wenham lived between th  years of 1824-1908; he was born in Kensington, London. His greates  contribution to England was his influence on the development of the stea  engine. However, in microscopy he was known to have made many of his ow  objectives as well as for others. He developed a number of binocular pris  designs beginning in 1853 to his most common and well know in 1860. By 1855 Wenham suggested that the correction collar act on the rear elements of th  objective thus perfecting the system and being the form that survives to thi  day. Until then the Ross system of moving the front element was used.  In 1850 Wenham rediscovered Goring's idea of using a single front element i  British objectives. French opticians had been acting on the idea for sometime. It was originally Dr. Goring who realized that over-correction was a problem an  suggested that the first element be a single lens instead of the usual compoun  element. This would allow the excess correction of the back combination t  balance the whole. Most British firms continued making front doublets for som  time.  In 1851, Wenham designed his metal paraboloid for dark-ground illuminatio  (first form) (LM/245). L. Martin uses the year of 1850 for Wenham's Paraboloi  design. Wenham’s paper on the subject was published in the Transactions i  1852; however, Smith & Beck manufactured one for the Great Exhibition in 1851 (JQMC, V.32, pp.290).  In 1853, Wenham presented his first paper "On the Application of Binocula  Vision to the Microscope"(Trans. Micro. Soc, Lond. 1-13, 1854). Smith & Bec  constructed the first stand using this system. This was the beginning of   number of designs using a refraction achromatic bi-prism, the last of which cam  in 1860. This final form consisted of a rhomboid prism, which reflected th  rays from half the objective aperture into a side tube. This arrangement wa  known as the Wenham binocular and lasted for over a half century. Certai  British makers continued to make the system until 1939 (LM, Hartley, 1991).  In 1870, following the death of Thomas Ross, Francis Wenham was persuaded t  join the firm as adviser (Ross & Co.) (1870-1882). He redesigned the Ros  bar-limb with the Jackson Limb and eventually used the Zentmayer horizonta  lever with its second slide as the fine adjustment (Ross Zentmayer). Wenha  also designed the famous Ross Radial Microscope of 1882 (LM/36). Earlier i  1875 he had written an article on the benefits of oblique illumination with hig  power objectives. In 1877, Wenham took out patent No.496 for an “Object stag  for Microscopes” designed to facilitate oblique lighting, a preoccupation whic  led to his new radial design of 1882.  At this point in his life and after the humiliation of the aperture war it wa  said that he gave up microscopy and never talked to any member of th  Microscopical Society again. J. Sollida     Brief History of Robert B. Tolles (American Microscope Maker)  For those who might be interested in a little history I have pu  together a few notes of interest concerning one of my favorit  historical figures. The information is primarily arranged by date. References are listed at the end. Jim Sollida   1821-83. Life of Robert B. Tolles, American microscope maker an  optician (Transactions, Am. Microscopical Society, Vol.98, No.1, 1979, pp.15). According to Dr. Cutter of New York (a contemporary), Tolles was born in West Winstead, Conn., in Sept 1827 (AMMJ,1893/302), but this is likely a typo as it should have rea  1821. A biographical account was included in the 1884 report of th  American Society of Microscopists, this also being published in th  American Monthly Microscopical Journal, Vol.V, Sept, 1884, No.9, pp.167. Here the location of his birth is listed at Winchester, Litchfield County, Conn. and his age was stated as 62 years. Tolle  apprenticed with Charles Spencer in Canastota, he remained wit  Spencer until 1858, when he started his own business in a small lof  in Canastota (AMMJ,1884/167). After moving to Boston in 1866-67, wa  first to make homogenous lens (1871) (AMMJ,1884/10). Began th  Boston Optical Works in conjunction with Mr. Charles Stodder in 1867- 68 and worked making objectives & stands until his death on Saturda  17th, November 1883. Mr. Oscar Richards of the American Optica  Company give the date of Tolles birth to be 1821 to 1883 (R,June,1964/124). In Three American Microscope Builders the date i  given as 1822 with the Winchester location, however, in Padgitt th  date is 1832 with the Winsted location. I tend to go with th  contemporary authors. His long time business partner Mr. Charle  Stodder passed away a few week after Mr. Tolles in January 1884 a  the age of seventy-five (TMB,1884/No.2/9). Stodder was also a wel  know diatomist.  1840, First immersion lenses made by Pro. Amici. According to Mayal  they were designed to be used with oils with the same refraction a  glass, homogeneous-immersion (MA/1119) (The Northern Microscopist, Vol.2, 82/307). This was not done with the conception of increasin  the apertures, that revelation was left to Tolles. Amici's work wa  intended to get more correction of the aberrations. However, the us  of oil on expensive slides was not readily excepted by the public, Amici gave up the oil system and adopted water as the immersion flui  (MA/1119).  1843, The year that Robert Tolles was returning from a visit with hi  uncle near Rochester and on his way home he stumbled into the shop o  Spencer in Canastota. On that day he decided he wanted to be a  optician. He made arrangements with Spencer for an apprenticeshi  (1852) and remained with him until 1858 (Three American Microscop  Makers).  1855, Tolles "Holosteric" or solid eyepiece. Robert Tolles invente  same while working for Spencer. The patent date is Sept 25, 1855, U.S. Pat. No.13603. (Date is stamped on the actual eyepiece). Th  solid eyepiece was manufactured much like the Coddington lens. Th  idea was to eliminate as many optical surfaces as possible. This wa  thought to be of value for the high powered eyepieces, includin  magnifications of 20X, 80X and even 120X (LM/53).  1857-8, Robert B. Tolles began working for himself after a  apprenticeship with Charles Spencer. He began in a small loft i  Canastota (RH/18). At first he primarily made telescopes. H  continued in Canastota until 1866-67 at which time he moved to Bosto  where he took charge of the Boston Optical Works, at 66 Milk St. H  now was associated with a partnership that included Charles Stodde  and several other Boston businessmen. In 1872 this partnership wa  dissolved leaving Tolles to continued the work at the BOW until hi  death in 1883. It seem that C. Stodder continued to handle th  business end of the works, leaving Tolles free to experiment an  build instruments. By the mid 1870's (ca.1876) the new address wa  at: Charles Stodder, Rialto, Room 36, 131 Devonshire Street, Boston.  1858, Tolles constructed objectives with two exchangeable fron  elements, one for dry work and the other for water immersio  (TAMB/38) (AMMJ,1884/168). In a meeting of the Boston Society o  Natural History (1867), Charles Stodder demonstrated a Tolles 1/10t  objective, both dry and wet (RI,97/88). In August 1873, he made hi  famous homog. immersion 1/10th (AMMJ,1884/168).  1859, Robert B. Tolles, at Canastota, Madison Co., N.Y. ran ad in J. King (1859) for his "adjustment for thin glass covers" in hi  objectives. He offered his 1/8th with an angle of aperture up t  175°. He offered higher powers up to 1/30 inch. under specia  contract. He also advertised his Solid Eye-piece (negative of larg  field). Advertised his amplifier, which not only doubled the powe  but also provided "perfect flatness of field"(J. King, ad, 1859).  1864, Tolles constructed his erecting stereoscopic binocular eyepiec  for Prof. H.L. Smith of Geneva, N.Y. (MMJ,Vol,6. July 1871/46). Carpenter (4th,ed) and Padgitt say the date was 1866 (HAM/57) (Hartly,LM/53/121). The date is 1864, the confusion arises do to th  fact that Prof. Smith exhibited the Tolles eyepiece in London, Carpenter assumed it was of Smith's making. This design was copie  by a German maker and sold as his own invention (AMMJ,1893/303).  1866, Tolles patented a binocular adapter for monocular microscope  (U.S. patent No.56125). The eyepiece could also be used on th  telescope. At the time he was still in Canastota (SMMA, No.23, 1995).  1866, Tolles first applied a small prism within an objective creatin  a New type of Vertical Illuminator (AMMJ,1893/303) (AMMJ,Vol 3/78). One of the first made was for Prof. R. K. Browne.  1867, Robert B. Tolles moved from Canastota to Boston where he alon  with Stodder opperated the Boston Optical Works. Charles Stodder an  several other Boston businessmen offered Tolles a partnership if h  would move his business to Boston (Scientific Medical & Mechanica  Antiqu./No.23, 1995). Other accounts state that Stodder and hi  investors made Tolles the superintendent of the busines  (R,June,1964/124), the date is sometimes given as 1866.  1867, Tolles began making his large "A" and "B" stands. Dr. J.E. Smith referred to the "B" as the "BB" stand. It was provided wit  two types of mechanical stage the first with coaxial screws and th  second operated by friction rollers, having 360° rotation on th  optical axis, the later stage costing more money (HS/48). Dr. J.E. Smith says the stands by Tolles "may be unhesitatingly pronounce  first-class. The workmanship is of the very highest order: th  circular stage can be so nicely adjusted as to allow of an entir  revolution, under a one-twenty-fifth objective, without the objec  being sensibly displaced. Any thing that Mr. Tolles makes is sure t  be made well"(HS/48). Dr. Smith's remarks coming in 1880.  1867, Tolles made immersion lenses, probably glycerin or water. I  1867 he made a 1/16th inch immersion that resolved Nobert's 19t  band, possibly for the first time. Witnesses: Mr. R. C. Greenlea  and C. Stodder, Boston (AMMJ,1893/303).  1870, Dr. George B. Harriman, a dentist, needed to demonstrate th  presence of nerves in teeth. In 1870, he commissioned Robert B. Tolles to design and produce an appropriate objective for the task. About three years later Tolles delivered an objective having a  equivalent focus of 1/75th inch, approx. 0.3mm. The price was $400. Some experts of the time suggested that such a short focal length wa  impossible, however, the Tolles objective achieved all that Dr. Harriman expected. Sometime later, the next owner, Dr. Ephrai  Cutter made a point of demonstrating its capabilities in Europe an  America, using the lens for microprojection on a screen 25 fee  square (BJM, 1965/V.14/472).  1871, Tolles demonstrated his homogeneous immersion objective usin  soft Canada balsam as a medium. At the death of Mr. Tolles th  editor of The Microscope, Mr. Stowell received an account of the lif  of Tolles from Mr. C. Stodder of Boston, Tolles business partner. Concerning the Tolles homogeneous objectives he records, "This h  demonstrated in 1871, but owing to the fact that at that time Canad  balsam was the only fluid known to possess the same refractive inde  as crown glass, his discovery remained useless until 1877, when Prof. Abbe discovered a fluid which was practical for such a purpose." (Th  Microscope, 1884, No.1, pp.5). However, attention was afforded Mr. Tolles on this concept in 1873, with the production of his 1/10t  immersion.  1871, A public debate began between Tolles and Wenham over th  question of the aperture of immersion objectives. The debat  actually began with a disagreement between Dr. Pigott and Wenham, drawing Tolles in with a challenge put out by Wenham. The followin  quote is by Mr. Wenham., "I challenge Dr. Pigott, or anyone, to get, through the object-glass with the immersion front, a greater angle, or any portion of the extraneous rays that would in the other case b  totally reflected, as no object-glass can collect image-forming ray  beyond this limit" (MMJ,V,1871/118). Much of the early debat  centered around a 1/10th and a 1/5th made by Tolles. Eventually, Tolles sent a 1/6th inch lens to Mr. Frank Crisp having an extr  front lens intended for immersion (MA/1119). This famous lens wa  the subject of a great deal of correspondence lasting from 1874- 1878. In 1878 Professor Keith computed the angular aperture of th  1/6th finding it to be of 110 degrees (R,78/142). This evidenc  finally settled the debate and completely vindicated Mr. Tolles. I  America the debate was known as "the war of the apertures." Throughout the debate, Mr. Tolles was assisted by Dr. J.J. Woodwar  of Washington D.C., and by Prof. Keith of Georgetown (HS/pref/11) (also see, R, June,1964/120).  1872, Partnership of Tolles and C. Stoddar ceased, Tolles the  continued on his own until his death. According to Hagelstein, Tolles worked under the name of the Boston Optical Works until 1871 when it was thought best to continue again under the name of Tolle  (RH/18). It is possible that C. Stoddar continued to sell Tolle  stands under the name of the Boston Optical Works as he wa  considered sole agent of Tolles.  1873, In August of 1873, Robert Tolles made a 1/10th inch objectiv  for homogeneous immersion in Balsam, having an aperture of 110 degrees or 1.25 n.a. (TAMB/38)(AMMJ,1884/168) and being a thre  system lens. This represents the first true homogeneous immersio  system for the microscope (B/245) (LM/36/39) (JQMC, V.32/294). Th  same month he made his first lens of the duplex front formula,   1/5th glycerin immersion of 110° balsam angle (n.a. 1.27) (TAMB/38). Both passed into the possession of the Army Medical Museum a  Washington, both used in softened balsam (AMMJ,1884/168). In 1874 his formula and objective were sent to England for inspection an  submission in the Journal of the RMS. In 1873 he also made his 1/5t  at N.A. 1.27 (duplex glycerine) and 1/10th at N.A. 1.27 (TAMB/38). This was partly in response to Wenham's denial of the ability o  immersion to effect an angular aperture greater then 180° in ai  (R,June,1964/120).  1873, In 1873-74, R.B. Tolles produced his "Duplex" or four-syste  objective glasses, the first example being an immersion lens i  glycerine, a 1/5th (TAMB/38). In 1874, Tolles requested Dr. J. Edward Smith of Cleveland, to report on a 1/6th duplex of 180° (HS/pref.). Dr. Smith confirmed the new lenses excelled all other  including higher magnifications such as the 1/15th (HS/pref./110). He then received a Tolles 1/10th "duplex" which was judged eve  better. Latter that year (1874) Dr. Smith received a 1/10th from Mr. Herbert Spencer (different formula then the Tolles), "the performanc  of which is not excelled by any glass yet made, be it a fifth or   fiftieth" (HS/110). There is some doubt if Dr. Smith was using th  Tolles in balsam as intended.  1873, Tolles designed an instrument for measuring the aperture of hi  objectives. He described it as "An apparatus for obtaining th  balsam angle of any objective" (MMJ,73/212).  1874, Mr. R. Keith published in the Monthly Microscopical Journal, proof of the expanded aperture of the Tolles 1/10" objective. Tolle  had described his 1/10th in Nov. 1873 along with its aperture. Th  significance of this debate was the fact that an immersion objectiv  could have a greater aperture than corresponds to the maximu  possible for a dry lens. With Tolles objectives the front lens wa  immersed in balsam having a similar refractive index as the fron  element, thus establishing a homogeneous system (MA/1119). Tolle  distinctly understood the influence of the use of higher refractiv  media. By performing tests, Dr. J.J. Woodward confirmed that "th  definition unmistakably better than with water immersion" (MMJ,XII,74/127). Both Professor Keith and Dr. J.J. Woodward gave   detailed computation of ray paths through the Tolles balsam immersio  1/10th inch (R,June,1964/120). The Zeiss oil-immersion lenses wer  not issued until 1878 (MA/1120). As for who first develope  the "homogeneous-immersion formula" with the intention of increasin  aperture, Mayall says that "Mr. R.B. Tolles stands alone as th  inventor" (MA/1120).  1874, Tolles 1/6th immersion objective, sent to England and used t  persuade the Society in the debate with Wenham over the limits o  aperture. The objective was owned by Frank Crisp and mentioned i  the RMS Journal of 1874. In 1878 Professor Keith computed th  angular aperture of the 1/6th finding it to be of 110 degree  (R,78/142). This evidence along with the endorsement of Prof. Stoke  (an English physicist) finally settled the debate (TAMB/47).  1877, In 1877 Tolles applied for a patent for his Traverse Sub-stag  (RMS,1880/1064) (U.S. Patent No. 198782 and 198783). This was a  apparatus for obtaining maximum oblique illumination.   hemispherical lens comes in immersion contact with the slide, while   condenser adjustable in a circular groove illuminates sam  (MA/1102).  1877, Zeiss produced Abbe's oil immersion objectives, which becam  known as "homogeneous" immersion (Innovation, No.1, 1996). Mayal  says the date was 1878 (MA/1119) (WU/175). Abbe stated that the oi  system was suggested to him by J.W. Stephenson (Treasure of th  RMS). However, Mayall confirms that the homogeneous-immersion syste  was due to Robert Tolles and his use of soft balsam (MA/1119). Warner states that the "oil immersion" objective was introduced i  March 1887 by Carl Zeiss (RI,97/88), introduced meaning available t  the public.  1879, John Mayall, wrote that he tested the best objective  available. He compared the Tolles 1/4th and 1/8th against the bes  lenses "by English, French, and German opticians," includin  immersion objectives by the most renowned makers in Europe. H  concluded that "without reserve of any kind, I say these lense  (Tolles) are the finest I have ever seen." He also stated, "I find, on the most severe test, there is in Tolles' lenses a bette  correction for spherical aberration" (HS/111).  1880, Dr. J. Edward Smith, said of R. Tolles, "who with almos  superhuman genius and energy grapples with the very laws of optics, and bends them to his inflexible will" (HS/102).  1880, Dr. J. E. Smith, describes the Tolles "duplex" object-glasse  as "a four system immersion, as distinguished from the older for  having a single front" (HS/125). By 1880, Mr. Tolles and Spence  were both making objectives of 120° balsam aperture (HS/125).  1882, E. Wheeler, 48, Tollington Rd, Holloway, N. was the Londo  Agent for R. B. Tolles (RMS/82/ad)  1883, Robert Tolles died, Nov 17, 1883 at Massachusetts hospital, Boston. Charles X. Dalton took charge of Boston Opt. Works (1883- 95), after the death of Robert Tolles. He was known to continu  making microscopes but with his signatures hidden. Dalton was   workman for Tolles doing his brass work (R,June,1964/124). J. Sollida   Abbreviations and references:  (AMMJ)=The American Monthly Microscopical Journal (1880-1901). Edite  by Romyn Hitchcock.  (B)=Bradbury (1969)=The Evolution of the Microscope (1967)  (BJM)=The Microscope, The British Journal of Microscopy an  Photomicrography, Barron.  (HAM)=Short History of the Early American Microsocpes., Padgit  (1975).  (HS)=How to See with The Microscope; (1885, edition) by J. Edward  Smith.  (LM)=The Light Microsocpe, by W.G, Hartley (1993)  (MA)=Mayall's, Cantor Lectures (1886-88). Royal Society of Arts.  (MMJ)=The Monthly Microscopical Journal, Transactions of the RM  (1869-1877).  (RH)=Robert Hagelstein, History of the Microscope, N.Y.M.S, Bulletin, Vol.2, No.1, April 1944, pp.1-19.  (RI)=Rittenhouse., Journal of the American Scientific Inst. Enterprise. Ed. D. J. Warne   (R) or (RMS)=Journal of the Royal Microscopial Society (1878 to th  present) (RMS).  (SMMA)=Scientific Medical & Mechanical Antiques, Greybird (America  Artifacts).  (TAMB)=Three American Microscope Builders, pub. by A O Company (1945).  (TMB)=The Microscopical Bulletin, Optician's Circular. James W. Queen & Comp.   Dear Jim,  Thankyou for a truely excellent paper on Tolles. It is a remarkabl  story, and only goes to show how careful you have to be wha  you 'stumble' into - it can change your whole life! I have a numbe  of pieces written by Wenham in 'The English Mechanic and World o  Science' in the 1890s. If you would like a copy, I will .pdf them an  send them to you. I don't know if I can post .pdfs to this site, bu  if you contact me on my work e-mail, mervyn_hobden@d...,   will send them direct. I have forwarded a copy of your piece to th  owner of the Tolles 1/10", and I hope to be able to take some mor  pictures through it shortly. I also hope to be able to post som  pictures taken with early Zeiss, Leitz, water immersion objectives, and a Spencer APO NA 1.4 homogeneous. My own opinion is that the bes  objectives of the 19th century are difficult and expensive to equa  today. Even Olympus have their APOs assembled in South China, wher  skilled labour is still cheap. Also, to get the best out of thes  objectives, you need a microscope with a draw tube, as well as   first class condenser. Not much use putting them on an 'Ultraphot'! Thankyou again, to understand a subject fully, you need to know it  history, and you have demonstrated that very well.  Sincerely, Mer   TOLLE     Robert B. Tolles, was born 1822, 1823, or 1825 (various sources) in  Connecticut, and had little formal education.  Circa 1843, he was apprenticed  to Charles Spencer, and in 1858 established his own business in Canastota N.Y.   By 1859, he was fabricating microscopes with Charles E. Grunow (most likely a  relative of the Grunow brothers, microscope makers), who made the mechanical  parts while Tolles made the objectives.  An 1860 census notes three employees  and annual production of 6 microscopes ($600) and 68 objectives ($1778) by  Tolles.  An inverted microscope won a prize in 1860.    An 1859 advertisement for microscope objectives includes notes on telescopes  and his solid eyepiece.  Also described is an 'amplifier' that increases the  magnification of a microscope, provides a flat field, and reduces secondary  spectrum.  This was a concave / convex lens inserted into the bottom of the  microscope draw tube; not a Tolles invention but much improved by him.  In  1879, this amplifier was said to double the magnification of a particular  combination of objective and eyepiece without disturbing the corrections; and  that higher magnification amplifiers using a different design were also  available.  Carpenter describes the amplifier thus (excerpts): 'a concave lens  between the objective and the eyepiece, magnifying power augmented, long since  introduced into telescopes, first made effective (microscopes) by Mr. Tolles,  an achromatic concavo-convex lens behind the objective, the power of which it  doubles'.  Tolles' 1879 catalog lists an amplifier for telescopes, which would  be a Barlow or Smyth lens.    Tolles' solid eyepiece reduced glass / air surfaces to two by cementing two  planoconvex elements, and was used in telescopes and microscopes.  It was  patented by Tolles in 1855 (U.S. 13,603), although Spencer was part of its  development and also manufactured them, and August Stendicke, a German lens  maker for Tolles and Spencer, knew of previous similar designs.  The patent  does not cover all such cemented doublets, but only those with a focal plane  within the lens, at which point Tolles placed a reticle scale.  The patent can  be found at the USPTO site:     http://164.195.100.11/netahtml/srchnum.htm      The 1879 catalog lists the Tolles's Patent Solid Eye-piece in 1/2", 3/8", 1/4",  and 1/8" sizes at $8 and $12; and the Tolles's Solid Orthoscopic Eye-piece, 1  inch, with higher powers available, also useable as an achromatic condenser.      The major innovations of Tolles were in microscope optics.  He pioneered the  immersion objective (homogeneous, meaning the liquid media was of similar  refractive index to glass); and fabricated very short focal length objectives  (to 1/75 inch), & of very high numerical aperture, up to 180 degrees 'angle of  aperture'.  The correcting collar was developed by Tolles and Spencer, used to  correct spherical aberration introduced by differing thicknesses of cover  slips, using a ring on the barrel to move the center elements of the objective.   In 1866, Tolles developed a vertical illumination system, his 'interior  illuminator', that used a prism behind the front lens of the objective to  reflect light to the object.  He patented a swinging substage, that varied the  angle of illumination above or below the stage; and two other microscope  illumination patents are 198,782 and 198,783.    Some of his objectives were comprised of seven individual lenses.  Many  contemporary microscopists found his products to be the best in the world.    Tolles patented his binocular adapter in 1866, (U.S. Patent No. 56125),  priced at $80. in 1879, and sold for microscopes and also telescopes.  This is  an unusual symmetrical design, where the light from the objective enters a  small equiangular prism placed at focus, and is split by the prism into two  deflected beams, which are then made parallel by two trapezoidal deflecting  prisms.  Padgitt notes that Edmund Hartnack of Paris and Potsdam devised a  similar system at about the same time; and that Tolles' system was copied by  William Ladd and Abbe & Zeiss.    Circa 1864, Tolles made a small quantity of binoculars (no doubt Galilean  field glasses) for the U.S. Navy.  James M. Gillis of the Navy wrote that they  were superior to European models but not good enough.  This reference to an  otherwise completely unknown binocular is from a letter from Gillis to Alvan  Clark & Sons, noted in Warner & Ariail.    At an exhibition in Boston in 1865, Tolles displayed a telescope of 1 1/2  inches aperture, 4 1/2 inches focal length, with a binocular eyepiece providing  15 power, at $100.  In 1867 was shown a 7/10 inch aperture, 4 inch focal  length, 13x telescope through which the satellites of Jupiter could be viewed.   By 1869, he had completed a 1 inch f/4 and a 1.45 inch f/4.  These short focus  instruments were very unusual or unique in their time.  An instrument described  as a Tolles micro-telescope in 1870 was a 1 inch f/6 objective with a small  microscope used as an erecting eyepiece, and providing 40 or 50 power.    In 1867, Tolles moved to Boston as a partner in Boston Optical Works,  incorporated with $9,000 in shares, at 66 Milk St., then 131 Devonshire St,  Boston.  The company failed in 1871, at least partly because Tolles'  perfectionism was contrary to reasonable production schedules.  He retained the  company name, located at 40 Hanover Street, working mostly by himself, with  only a few employees, including John Green, Orlando Amos, O.T. May (son in law  of Charles Spencer), and Clarence Spencer (son of Charles Spencer).  Charles  Stodder had been selling Tolles' instruments since 1860, was treasurer of the  Works, and continued marketing Tolles' output.    The catalog: "Charles Stodder.....sole agent for the sale of Microscopes and  Telescopes made by R.B. Tolles", from 1879, includes the following telescopes: --1/2 inch objective, solid eyepieces of 10x to 18x, 6.5 inches opened, $25,  $33 with stand, 'The Pedestrian's Telescope.' --1 inch lens of 5 inch focus, pancratic eyepiece of 12x to 24x with higher  magnifications available, on stand, $70. --2 1/2 inch lens, 22 to 27 inch focus, 23x to 46x pancratic eyepiece, alt / az  mount on iron tripod, $175; on engineers tripod $150;  with two astronomical  eyepieces to 130x, amplifier, prism diagonal, and sun glass, $250, 'The High  School Telescope'. --4 inch lens, on iron tripod, $300.  Mentioned is a 4.1 inch of 42 inches  focal length, with an alt / az mount on an iron tripod. --"Telescopes of any aperture, of unusually short focal length, made under  special contract"    The 1879 catalog includes a report from an 1869 exhibition in Boston, noting  that the Tolles binocular eyepiece can also be used in telescopes.  On exhibit  were a 5 inch refractor of 35 inches focal length, on an equatorial mounting,  with 80x and 160x eyepieces; a 1 inch pancratic telescope of 4 to 12 inches  focal length; and a 1 1/2 inch refractor of 6 inch focal length.  Telescopes  had been sold to Washington Academy, East Machias, Maine; Howland School, Union  Springs, N.Y.; and the High School in New Bedford, Mass.; various individuals  who were customers are also mentioned.    Also cited in the 1879 catalog is Benjamin Gould's 1871 report on viewing  15th magnitude stars from Cordoba, Argentina with his 5 inch f/7 tapered wood  tube, equatorial comet seeker.  He also arranged the purchase of another Tolles  telescope for the Argentine National Observatory, which he directed.  Gould  wrote in 1874 that he purchased his Tolles 'about a dozen years ago', and that  its field of 2 degrees allowed a view of the entire corona during the total  eclipse of 1869. "The telescope...has rendered important service in both  hemispheres."  He later presented it to Seth Chandler, his assistant, whose  descendants gave it to the National Museum of American History, where it is  catalog 80.709.1    Charles X. Dalton was an employee of Tolles in Canastota, and after Tolles'  death 17 Nov. 1883, returned to the business to continue production of  microscopes.  'Charles X. Dalton, successor to the late R.B. Tolles, Boston  Optical Works', located at 30 and 48 Hanover Street, Boston, advertised in  1895, selling Tolles objectives and Tolles triplet magnifiers in silver cases.    Currently, a 5 inch refractor with a 45 inch tube and a Huygenian eyepiece  is located in the planetarium of the University of Maine.  References:  Blackham, George. Memoir of Robert B. Tolles.  Proceedings of the American  Society of Microscopists (1884).  Reprinted in: Three American Microscope  Builders. Buffalo: American Optical Co., 1945.  Carpenter, William. The Microscope and its Revelations. N.Y.: William Wood,  1883.  Gage, Simon.  Microscopy in America 1830-1945.  Transactions of the American  Microscopical Society 83:4 (Oct. 1964), Supplement.  Larue, Budd. Robert B. Tolles and the Cone-Fronted Objective. Rittenhouse 12  (1998) 55-64.  Padgitt, Donald L.  A Short History of the Early American Microscopes.  Microscope Publications: London & Chicago, 1975.  Warner, Deborah Jean. The Microscopes and Telescopes of Robert B. Tolles.  Rittenhouse 9 (1995) 65-83.  Warner, Deborah Jean & Ariail, Robert B.  Alvin Clark & Sons, Artists in  Optics, 2nd ed. Richmond: Willman-Bell, 1995.  Van Vleck, Richard.  Robert B. Tolles, American Microscope Maker.    <www.americanartifacts.com/smma/tolles/tolles1.htm>  ====================================