Test Objects for Microscopes

This article draws on material from my book The microscope and the eye: A history of reflections, 1740–1870 (Chicago, 2007), chap. 5. In the present essay, I develop those aspects of the story that go beyond the book's scope as well as the general implications of the case.

See Gooday G. , “‘Nature’ in the laboratory: Domestication and discipline with the microscope in Victorian life science”, The British journal for the history of science, xxiv (1991), 307–41, and “Instrumentation and interpretation: Managing and representing the working environment of Victorian experimental science”, in Lightman B. (ed.), Victorian science in context (Chicago 1997), 409–37.

Gooday , “Instrumentation” (ref. 2), 423.

My discussion ranges across different countries, and for the most part, I do not take national differences into account. This would be a topic for further, more in-depth studies of the specific activities surrounding test objects. My aim in this paper is to capture the overall dynamics of the practice of using test objects.

Herschel W. , “On the power of penetrating into space by telescopes; with a comparative determination of the extent of that power in natural vision, and in telescopes of various sizes and constructions; illustrated by select observations”, Philosophical transactions of the Royal Society of London, xc (1800), 49–85. The Oxford English dictionary identifies Herschel's paper as the original source of the term. Astronomy remained the reference point for writers on test objects, see Nobert F. A. , “Ueber die Prüfung und Vollkommenheit unserer jetzigen Mikroskope”, Annalen der Physik und Chemie, lxvii (1846), 1846–85, p. 174; von Mohl H. , Mikrographie, oder Anleitung zur Kenntniss und zum Gebrauche des Mikroskops (Tübingen, 1846), 180.

Goring C. R. , “On achromatic microscopes with a description of certain objects for trying their definition”, The quarterly journal of science, literature, and art, xxiii, n.s. i (1827), 410–34, p. 418.

Goring , “On achromatic microscopes” (ref. 6), 418–19.

Pritchard A. , “Test objects”, London and Edinburgh philosophical magazine and journal of science, ii (1833), 335–44, p. 335. This is the slightly abridged version of the chapter on test objects in Pritchard's The microscopic cabinet of select animated objects; with a description of the jewel and doublet microscope, test objects, &c (facsimile edn, Lincolnwood, 1987).

Harting P. , Das Mikroskop. Theorie, Gebrauch, Geschichte und gegenwärtiger Zustand desselben. Theorie und allgemeine Beschreibung des Mikroskopes, i, 2nd edn (Braunschweig, 1866), 275n. See also Smith H. A. , “Memoir of Charles A. Spencer”, Proceedings of the American Society of Microscopists, vi (1882), 1882–74, p. 66.

Carpenter W. B. , The microscope and its revelations, 6th edn (New York, 1883), 161.

Nägeli C. Schwendener S. , Mikroskop: Theorie und Anwendung desselben, i (Leipzig 1867), 79, 83.

Nägeli Schwendener , Mikroskop (ref. 11), i, 120.

Vorce C. M. , “Penetration in objectives: Is it a defect or an advantage?”, Proceedings of the American Society of Microscopists, ii (1880), 70–75.

See, in particular, Jacob Cox's account of the “aperture controversy” between the American maker Robert Tolles and Francis Wenham on the other side of the Atlantic: Cox J. D. , “Annual address of the president: Robert H. Tolles and the angular aperture question”, Proceedings of the American Society of Microscopists, vi (1884), 5–39.

Gill T. , “On the microscope”, Gill's technological repository; or, discoveries and improvements in the useful arts, ii (1828), 95–99, 138–49, 193–201, 257–64, 321–30, p. 96.

v. Jacquin J. , “Bemerkungen über Mikroskope und ihren Gebrauch für Naturforscher”, Zeitschrift für Physik und Mathematik, v (1829), 129–60, p. 137.

Gill T. , “On the microscope”, Gill's technological repository; or, discoveries and improvements in the useful arts, iii (1829), 1–14, 75–82, 129–49, 193–206, 257–63, 321–27, p. 138; Pritchard, Microscopic cabinet (ref. 8), 151.

See, for instance, the catalogues issued around 1830 by the Viennese maker Ploessl ( Ploessl G. S. , “Verzeichniss der gangbarsten optischen Apparate, welche von G. S. Plössl, privilegirtem Optiker in Wien, neue Wieden, Salvatorgasse Nro 321, für beigesetze Preise verfertiget werden”, Zeitschrift für Physik und Mathematik, iv (1828), 121–8; “Neues Verzeichniss der gangbarsten optischen Apparate, welche von G. S. Plössl, Optiker und Mechaniker in Wien, neue Wieden, Salvatorgasse Nro 321, für beigesetze Preise in Conventions-Münze oder Augsb. Courant verfertiget werden”, Zeitschrift für Physik und Mathematik, vii (1830), 1830–28), and, in 1840, by the American maker Spencer (cf. Smith , “Memoir” (ref. 9), 54). See also Vogel J. , Anleitung zum Gebrauch des Mikroskopes zur zoochemischen Analyse und zur mikroskopisch-chemischen Untersuchung überhaupt (Leipzig 1841), 119–20.

Gill T. , “On Professor Amici's and other microscopes”, Gill's technological repository; or, discoveries and improvements in the useful arts, i (1827), 16–19, p. 16.

Gill , “Amici's microscopes” (ref. 19), 18.

Pritchard , “Test objects” (ref. 8), 335.

See, e.g., Anon., “Review: The microscope and its revelations”, London quarterly review, lxvii (1857), 289–315, pp. 290–1; see also Royston-Pigott G. W. , “On a searcher for aplanatic images applied to microscopes, and its effects in increasing power and improving definition”, Philosophical transactions of the Royal Society of London, clx (1870), 1870–603, p. 591; Smith , “Memoir” (ref. 9), 63; Carpenter, Microscope (ref. 10), 170; Walmsley W. H. , “Some new points in photomicrography and photo-micrographic cameras”, Transactions of the American Microscopical Society, xvii (1896), 1896–9, p. 340.

Bowerbank J. S. , “Reminiscences of the early times of the achromatic microscope”, Monthly microscopical journal, iii (1870), 281–5, p. 281.

For the competition between English and Continental craftsmen, see Jackson M. W. , Spectrum of belief: Joseph von Fraunhofer and the craft of precision optics (Cambridge, 2000).

Gill , “On the microscope” (ref. 17), 138.

Pritchard , Microscopic cabinet (ref. 8), 151.

In his 1882 memoir of the instrument maker Charles Spencer, Smith quoted extensively from letters written in the 1840s (both personal correspondence and letters to journal editors). One microscopist found Spencer's lenses far superior to those of Chevalier, stating that with them he had been “able, without difficulty, to see the cross-lines on the Navicula hippocampus (the most difficult test object now known to me, and which was sent to me from England as the test object par excellence)” (Smith, “Memoir” (ref. 9), 57).

Smith , “Memoir” (ref. 9), 62.

The bulk of Friedrich Reinicke's booklet Contributions to recent microscopy, for instance, is devoted to a comparison of English and German microscopes, carried out with test objects ( Reinicke F. , Beiträge zur neuern Mikroskopie. I. Die Leistungen der neueren Mikroskope und die Prüfung derselben. II. Die Leistungen der englischen Mikroskope, gegenüber den deutschen. III. Das Einsammeln und Präpariren der Bacillarien. Mit 9 Abbildungen von Pleurosigma Angulatum als Probeoobject (Dresden 1858), chap. 2).

Detmers H. J. , “American and European microscopes”, Proceedings of the American Society of Microscopists, x (1888), 149–54, p. 150.

Detmers , “American and European microscopes” (ref. 30), 152.

Goring , “On achromatic microscopes” (ref. 6), 422–3.

Pritchard , Microscopic cabinet (ref. 8), 137.

Pritchard , Microscopic cabinet (ref. 8), 141.

“Artificial stars” are little globules of mercury. See Harting , Mikroskop (ref. 9), 281, for a description of how to make them.

Harting , Mikroskop (ref. 9), 283.

Frey H. , The microscope and microscopical technology (New York 1872), 56.

Pritchard , Microscopic cabinet (ref. 8), 141.

For example, in their manual of microscopy, the botanists Carl Nägeli and Simon Schwendener pointed out that test objects were perfect practical tools to evaluate the performance of a microscope “if one wishes to avoid testing all the peculiarities and errors of construction on which it [the quality] depends” (Nägeli and Schwendener , Mikroskop (ref. 11), 119).

On the establishment of medical microscopy, see Jacyna L. S. , “John Hughes Bennett and the origins of medical microscopy in Edinburgh: Lilliputian wonders”, Proceedings of the Royal College of Physicians of Edinburgh, xxvii (1997), 12–21; and “‘A host of experienced microscopists’: The establishment of histology in nineteenth-century Edinburgh”, Bulletin of the history of medicine, lvii (2001), 2001–53.

Bennett J. H. , An introduction to clinical medicine: Six lectures on the method of examining patients; percussion; auscultation; the use of the microscope; and the diagnosis of skin diseases, 2nd edn (Edinburgh, 1853), 66. Bennett referred here to “histological molecules”, particles that are smaller than cells but not as small as the molecules of the chemists (on Bennett's histological molecules, see Strick J. , Sparks of life: Darwinism and the Victorian debates over spontaneous generation (Cambridge, 2000), 42–47).

Purkinje J. E. , “Mikroskop”, in Wagner R. (ed.), Handwörterbuch der Physiologie, ii (Braunschweig, 1844), 411–40; quoted after Purkinje, Opera omnia, iii (Prague, 1939), 153.

Frey , Microscope (ref. 37), 62.

Carpenter , Microscope (ref. 10), 165 n.

Goring C. R. , Micrographia: Containing practical essays on reflecting, solar, oxy-hydrogen gas, microscopes, micrometers, eye-pieces, &c. &c. With researches concerning the most eligible methods of constructing microscopes, and instructions for using them (London, 1837), 99–100. See also Reinicke , Beiträge (ref. 29), 38.

See the reference to “diatomaniacal studies” in Packard A. S. , “A chapter on mites”, The American naturalist, iii (1869), 364–73, p. 364.

Carpenter , Microscope (ref. 10), 165. However, Carpenter himself seems to have had his share in this frenzy. In 1875, the Journal of the Society of Arts printed a summary of the first of a course of juvenile lectures Carpenter had given, in which he had pointed out the peculiar markings of diatoms that made them particularly interesting to microscopists ( Carpenter W. B. , “Juvenile lectures: The wonders of the microscope”, Journal of the Society of Arts, xxiv (1875), 123). See also Frey's defence of the endeavour to discover ever finer lines (Frey, Microscope (ref. 37), 63), and T. F. Smith's apology for the study of diatoms. Smith complained that “the microscopist who indulges in it is looked upon as nothing better than a trifler in science. But I think this stigma is an unjust one if we look at the important part the resolution of diatoms has played in the development of the modern objective, and thus placed in the hands of microscopists generally an efficient instrument of research, without which many pages of Nature must have remained a sealed book” ( Smith T. F. , “Ultimate structure of the pleurosigma valve”, Journal of the Royal Microscopical Society, 1889, 812–17, p. 813).

Anon., “Review” (ref. 22), 291–2. This is the review of the 1856 edition of Carpenter's book. 49. Gill , “Amici's microscopes” (ref. 19), 18.

Gill , “On the microscope” (ref. 15), 96.

Gill , “On the microscope” (ref. 15), 97.

Pritchard , “Test objects” (ref. 8), 336.

Pritchard , Microscopic cabinet (ref. 8), 142.

Pritchard , Microscopic cabinet (ref. 8), 143.

“Stable” means here that the individual test object must keep its form during the testing process; for instance, it should not deteriorate too quickly. This appears obvious; and it does not seem to have posed a serious challenge because it is rarely discussed. However, there are indications that it was hard to keep the test objects stable for a longer period. Nobert mentioned that some of the test objects he had at his disposal were damaged due to the chemicals that had been used for mounting them ( Nobert , “Prüfung” (ref. 5), 105).

Pritchard , Microscopic cabinet (ref. 8), 142.

For information about Nobert's life and research, see Turner G. L'E. , “The contributions to science of Friedrich Adolph Nobert”, in his Essays on the history of the microscope (Oxford, 1980), 141–58.

For measurements of the number of bands and the distances of the lines, see Turner , “Contributions” (ref. 57), 145–6. According to Turner, the first test plate consisted of ten bands with lines between 1/1000 and 1/4000 Paris line (2.2256mm). Nobert's final 20-band test plate was ruled at an average spacing of 0.11μm in its finest band.

Nobert , “Prüfung” (ref. 5), 174.

Turner , “Contributions” (ref. 57).

Schultze M. , “Die Nobert'schen Probeplatten”, Archiv für mikroskopische Anatomie, i (1865), 305–7, p. 306; Nobert F. A. , “Die höchste Leistung des heutigen Mikroskops und seine Prüfung durch künstliche und natürliche Objekte [1861]”, Mittheilungen aus dem naturwissenschaftlichen Vereine von Neu-Vorpommern und Rügen in Greifswald, 1882, 92–105, pp. 93–95.

Mayall J. , “Nobert's ruling machine”, Journal of the Society of Arts, 1885, 707–13, p. 709.

Frey , Microscope (ref. 37), 70; see also Pohl J. J. , “Ueber mikroskopische Probeobjecte, insbesondere Nobert's Testobject-Platte”, Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften. Mathematisch-naturwissenschaftliche Classe, xl (1860), 63–97, pp. 87–88; and Vogel J. , Das Mikroskop und die Methoden der mikroskopischen Untersuchung in ihren verschiedenen Anwendungen, 2nd edn (Berlin, 1877), 89.

As Nägeli and Schwendener observed: One could “with certainty state a priori” that a complete identity of the bands could never be obtained with any machine (Nägeli and Schwendener, Mikroskop (ref. 11), 141, see also von Mohl , Mikrographie (ref. 5), 191). In a letter to Abbe, written in 1875, Nobert conceded that making the rulings was extremely difficult (quoted in Turner, “Contributions” (ref. 57), 147–8). But ultimately, he rejected the critique levelled at his test plates (Nobert, “Leistung” (ref. 61), 97); see also Schultze's essay, which declares that three of Nobert's test plates were “unbelievably” similar (Schultze, “Probeplatten” (ref. 61), 306).

Mayall , “Ruling machine” (ref. 62), 710.

Frey , Microscope (ref. 37), 63; see Harting , Mikroskop (ref. 9), 319.

Reinicke , Beiträge (ref. 29), 2–4.

Frey , Microscope (ref. 37), 64.

Mayall , “Ruling machine” (ref. 62), 708–9.

Nägeli Schwendener , Mikroskop (ref. 11), 140.

Nobert , “Leistung” (ref. 61), 162.

Frey , Microscope (ref. 37), 70.

Reinicke , Beiträge (ref. 29), 6–7.

Reade J. B. , “Microscopic test objects under parallel light and corrected powers”, Popular science review, ix (1870), 138–48, p. 140.

Morehouse G. W. , “The structure of the scales of Lepisma saccharina”, The American naturalist, vii (1873), 666–9, p. 666.

Anon., “Microscopy”, Popular science review, viii (1869), 206–9, pp. 207–8.

Mayall , “Ruling machine” (ref. 62), 710.

Frey , Microscope (ref. 37), 70; see also Nobert , “Leistung” (ref. 61). So Turner's comment that test plates “were, in fact, a standard” and therefore “unequivocable values can be given to resolutions reported in the literature for all those cases where one of Nobert's plates was used” must be taken cum grano salis (Turner, “Contributions” (ref. 57), 148).

In my book, I show that very often in the history of microscopy, the discrepancy of results was a driving force for reflections and experiments on the means of investigation ( Schickore , Microscope (ref. 1), 242).

See, e.g., Harting , Mikroskop (ref. 9), 310.

Hogg J. , The microscope; its history, construction, and application, being a familiar introduction to the use of the instrument, and the study of microscopial science, 6th edn (London, 1867), 64–66.

Howe L. , “An imperfection of the eye, and test objects for the microscope”, Proceedings of the American Society of Microscopists, vii (1885), 91–92.

Nägeli Schwendener , Mikroskop (ref. 11), 133.

Reade “Test objects” (ref. 74), 138.

The problem was, for Reade, that all devices had fixed apertures, a fault that his own remedied. He also commended the French microscopist Félix Dujardin for having developed the achromatic condenser.

Frey , Microscope (ref. 37), 65–66.

Morehouse , “Structure” (ref. 75), 666.

Kirsch A. M. , “Simple method of easily resolving microscopical test-objects”, Midland naturalist, i (1909), 26–27, pp. 26, 27.

Pritchard , “Test objects” (ref. 8), 336.

Jacquin , “Bemerkungen” (ref. 16), 144.

Pohl , “Probeobjecte” (ref. 53), 63.

Mayall , “Ruling machine” (ref. 62), 710.

Carpenter , Microscope (ref. 10), 161. Note that in Carpenter's classification, the term ‘penetrating power’ is used differently than in Goring's original explication of the term.

Woodward J. J. , “The use of amphipleura pellucida as a test-object for high powers”, The American naturalist, vi (1872), 193–7, p. 194.

Gooday , “Instruments” (ref. 2), 433.

Jacquin , “Bemerkungen” (ref. 16), 135.

Goring , Micrographia (ref. 45), 100.

Purkinje , “Mikroskop” (ref. 42), 131; Nägeli and Schwendener, Mikroskop (ref. 11), 134.

See Hogg , Microscope (ref. 81), 61–64.

Pohl , “Probeobjecte” (ref. 63).

See Hogg , Microscope (ref. 81), 61.

This passage is not included in the fourth edition of 1859.

Carpenter , Microscope (ref. 10), 146–7. For similar opinions, see also Harting , Mikroskop (ref. 9), 279, and Hogg , Microscope (ref. 81), 69–70.

Carpenter , Microscope (ref. 10), 161, see also 170. Amplifying Carpenter's message, his reviewer (that is, of the 1856 edition) praised Carpenter for having reminded those practitioners who had “vied in improving the lenses, so as to excel in the resolution of these tests” that microscopes “should possess other properties than clearness of definition; and that in gaining the one you may sacrifice others of equal worth” (Anon., “Review” (ref. 22), 290–1).

Carpenter , Microscope (ref. 10), 169.

Hogg , Microscope (ref. 81), 69.

The revolving stage allowed turning the object in order to view it in different illuminations. The object could of course also be turned by direct manipulation but this required great skill and created disturbances ( Reinicke , Beiträge (ref. 29), 11).

Vogel , Mikroskop (ref. 10), 86.

Nielsen J. E. , “Electron microscope reveals a possible valve structure of Amphipleura pellucida”, Transactions of the American Microscopical Society, lxvi (1947), 140–3, p. 140. For an investigation of Nobert's test plates with an electron microscope, see Turner , “Contributions” (ref. 57), 146–8.

Heidenreich R. D. , “A test object and criteria for high resolution electron microscopy”, Journal for applied crystallography, i (1968), 1–19.

See, e.g., Dennis M. A. , “Graphic understanding: Instruments and interpretation in Robert Hooke's Micrographia”, Science in context, iii (1989), 309–64; Harwood J. T. , “Rhetoric and graphics in ‘Micrographia”’, in Hunter M. Schaffer S. (eds), Robert Hooke: New studies (Woodbridge, 1989), 119–47.

Hooke R. , Micrographia, or some physiological descriptions of minute bodies made by magnifying glasses with observations and inquiries thereupon [1665] (New York, 1961), preface, n. p.

Pelisson D. , “Vergleichung der bekanntesten und besten Vergrösserungsgläser, nebst kurzer Nachricht von einigen im vorigen Jahr angestellten mikroskopischen Versuchen”, Beschäftigungen der Berlinischen Gesellschaft naturforschender Freunde, i (1775), 332–43. For references to additional articles presenting similar comparisons, see Ratcliff M. J. , “Testing microscopes between market and scientific strategies in the eighteenth century”, in Generali D. Ratcliff M. J. (eds), From makers to users: Microscopes and scientific practices in the 17th and 18th centuries (Florence, 2007), 135–54, pp. 151–2.

According to van Helden, the comparison of telescopes was common practice already in seventeenth-century Italy. At that time, the use of a piece of printed text as a standard in evaluating the performance of a telescope had become “fairly common” ( van Helden A. , “Telescopes and authority from Galileo to Cassini”, Osiris, ix (1994), 7–29, p. 25). But as Ratcliff's article indicates, in eighteenth-century microscopy the use of a standard of comparison had not become established.

Ratcliff , “Testing microscopes” (ref. 113), 142, 145.

See, e.g., Harting , Mikroskop (ref. 9), 275.