The Development of Micrometers in the Seventeenth,Eighteenth and Nineteenth Centuries

McKeon Robert M. , “Les débuts de l'astronomie de précision, 1: Histoire de la réalization du micromètre astronomique”, Physis , xiii (1971), 225–88; “2: Histoire de l'acquisition des instruments d'astronomie et de géodesie munis d'appareils de visée optique”, Physis , xiv (1972), 221–42. Govi's G. previously written history of micrometers, in Italian, is virtually unknown (“Della invenzione del micrometro per gli strumenti astronomici”, Bullettino di bibliografi di storia della scienze mathematiche e fisiche (Rome), xx (1887), 614–19).

This paper is derived from the author's unpublished Ph.D. thesis, “The precision screw in scientific instruments of the seventeenth to nineteenth centuries with particular reference to astronomical, nautical and surveying instruments”, Leicester University, 1989.

For a developmental history of heliometers see Fauque Danielle , “Naissance et évolutions de l'heliomètre 1748–1824”, unpublished doctoral thesis (3^e cycle), École des Hautes Études en Sciences Sociales, Paris, 1983.

O'Neill W. M. , Early astronomy: From Babylonia to Copernicus (Sydney, 1986), 124–7.

Dreyer J. L. E. , Tycho Brahe: A picture of scientific life and work in the sixteenth century (London, 1890), 39, 326–7.

Ibid. , 317–19.

Kellermann R. Kellermann R. Treuge W. , Die Kulturgeschichte der Schraube (Munich, 1962), 111–12, 116. Flamsteed also claimed that Emperor Ferdinand had conceived the idea of using screws for measuring, as was noted by Tycho Brahe. Ferdinand's instrument is described by Lucius Barrettus ( Historia celestis (Augsburg, 1666), 112) and in a letter from Flamsteed to Molyneux of 4 November 1686 in the Southampton Record Office ( The preface to John Flamsteed's Historia coelestis britannica , translated by Alison D. Johnson Allan Chapman (National Maritime Museum, Maritime Monographs and Reports no. 52; London, 1982), 205, fn. 133).

E.g. Wesley Walter G. , “The accuracy of Tycho Brahe's instruments”, Journal for the history of astronomy , ix (1978), 42–53; Allan Chapman , “Dividing the circle”, unpublished Ph.D. thesis, Oxford University, 1976 (British Thesis no. D26897/79) and “The accuracy of angular measuring instruments used in astronomy between 1500 and 1850”, Journal for the history of astronomy , xiv (1983), 133–7.

Comment made by Ludolf von Mackensen at the Scientific Instrument Society Symposium in London, Sept. 1988.

Moran Bruce T. , “German prince practitioners: Aspects in the development of courtly science, technology and procedures in the Renaissance”, Technology & culture , xxii (1981), 253–74, pp. 270–1.

See Ernst Zinner , Astronomische Instrumente des 11. bis 18. Jahrhunderts (Munich, 1979; 1st edn, 1956), 266–7, Max Engelmann , “Schraubenmikrometer-erstlinge”, Archiv für Geschichte der Mathematik der Naturwissenschaften und der Technik , x (1927), 295–7, and Kellermann Truege , op. cit. (ref. 7), 109–11. Kellermann and Truege's inscriptions for their photographs of the instrument indicate they thought that there were two instruments, made in 1609 and 1619, but this appears to be incorrect.

Leonhard Zubler , Novum instrumentum sciothericum … (Zurich, 1609).

Estimated from Engelmann , op. cit. (ref. 11), Fig. 1a.

Moran , op. cit. (ref. 10), 271.

Gascoigne's date of birth is sometimes erroneously given as c. 1612. David Gill in the ninth edition of the Encyclopaedia britannica (1878) (q.v. Micrometer) states that Flamsteed, in his Historia cœlestis britannica, included observations by Gascoigne extending from 1638 to 1643, and more were given in John Bevis (“Re Gascoigne's micrometer”, Philosophical transactions , xlviii (1753–54), 190–2). Gill's description of Gascoigne's micrometer is actually that given by Hooke of Townley's micrometer.

Gill , op. cit. (ref. 15).

Derek Howse , Francis Place and the early history of the Greenwich Observatory (New York, 1975), 30.

Van Helden Albert , Measuring the universe (Chicago and London, 1985), 118–19.

Peter Stephen Rigaud , Correspondence of scientific men (Oxford, 1841), 45–46.

The use of spiders' webs is discussed in Brooks Randall C. , “Methods of fiducial fabrication for 17^th–19^th c. micrometers”, Bulletin of the Scientific Instrument Society , no. 23 (1989), 11–14. Gaythorpe S. B. (“On a Galilean telescope made about 1640 by William Gascoigne, inventor of the filar micrometer”, Journal of the British Astronomical Association , xxxix (1929), 238–41) has computed the magnification and field of view of Gascoigne's Galilean telescope (made in Oct. 1640) but nothing is known of the properties of Gascoigne's Keplerian telescope(s) to which he applied the micrometer. See ref. 7 of Van Helden, op. cit. (ref. 18).

William Derham (“Extracts from Mr. Gascoigne's and Mr. Crabtree's letters proving Mr. Gascoigne to have been the inventor of the telescopic sights of mathematical instruments, and not the French”, Philosophical transactions , xxx (1717), 603–10) also had to put forth the case for Gascoigne having invented telescopic sights.

Richard Townley , “Of a letter … touching on the invention of dividing a foot into many thousand parts, for mathematical purposes”, Philosophical transactions , ii (1667), 457–8.

Robert Hooke , “A description of an instrument for dividing a foot into many thousands of parts …”, Philosophical transactions , ii (1667), 541–4. See Howse , op. cit. (ref. 17), Pl. XIIa, b. Flamsteed met Townley in 1671 at which time he studied the observations of Gascoigne, Horrocks and Crabtree. According to Howse Derek ( Greenwich time and the discovery of the longitude (Oxford, 1980), 23, note 7), Townley gave Flamsteed one of his micrometers. In a letter to Collins , dated 31 Jan. 1671/2 ( Rigaud , op. cit. (ref. 19), 126–9), Flamsteed states that he had sent plans for his micrometer to Collins and Townley and was waiting a response before divulging his design further. In the next letter dated 10 Feb. 1671/2 ( ibid. , 129–31), he sent Collins ten measures of the solar diameter but states that some were too large by virtue of his inexperience with such observations — a problem Allan Chapman also encountered (“Gauging angles in the 17^th century”, Sky & telescope , lxxiii (1987), 362–4). It should be noted that Wolf A. ( A history of science, technology and philosophy in the 16^th and 17^th centuries (London, 1950), 169) has incorrectly labelled the Townley micrometer as that of Gascoigne — an error that has been repeated often.

David Baxandall , “Early telescopes in the Science Museum from an historical standpoint”, Transactions of the Optical Society (London), xxiv (1922–23), 304–20, p. 311; Alan Chapman , Three north country astronomers (Manchester, 1982), 104.

Francis Bailey ( An account of the Rev. John Flamsteed, the first Astronomer Royal (London, 1835), 29) notes that Flamsteed's description of Townley's micrometer is in vol. xliii of Flamsteed's papers. He first saw Townley's micrometer in June 1670 and had received one of Townley's from Sir Jonas Moore by midsummer ( Baily , ibid. , 30, 109–10).

Hooke , op. cit. (ref. 23), 542.

Gunter R. T. ( Early science at Oxford , ii (Oxford, 1923), 309) is in error in stating that this screw was made by Townley from a simple screw.

Astronomical micrometer screws were made with the screw pitch suited to the scale divisions or magnification of the instrument, and they used pitches of 30, 40, 50, 60 or 100 TPI. For bench micrometers the linear size is important, and in the extreme require a very precise determination. In these instruments, the screw had to be of predetermined and precise pitch related to the units being measured. About 1875, Joseph Whitworth measured differences of one-millionth inch (0.000025mm) with a comparator, but this was a relative measurement and approximately 1000 times more accurate than the best nineteenth-century micrometers.

Baxandall ( op. cit. (ref. 24), 311) states that Gascoigne's micrometer had 100 divisions on the dial. Townley , op. cit. (ref. 22), 458.

Chapman says it was 40 TPI, op. cit. (ref. 8, 1976), 321.

Henry King , The history of the telescope (London, 1955), 99.

Reprinted in Histoire de l'Académie Royale des Sciences depuis 1666 jusqu'à 1699 , vii (1729), 118–30 and in McKeon , op. cit. (ref. 1, 1971), 249–54.

Cassini was the first to use a fixed thread perpendicular to the movable threads ( Nevil Maskelyne , “Directions for use of the common micrometer”, Philosophical transactions , lxii (1772), 46–53).

McKeon , op. cit. (ref. 1, 1971), 272.

Ibid. , 269.

Adrien Auzout , Traité du micromètre, ou manière exacte pour pendre le diamètre de planètes et la distance entre les petites étoiles (Paris and Amsterdam, 1667), 6–8. Also reprinted in Mémoires de l'Académie Royale des Sciences , vii (1729), 1128–20; McKeon , op. cit. (ref. 1, 1971), 276–7. The methods of and errors arising due to the mode of calibration are dealt with in Brooks Randall C. , “Errors in measurement of the solar diameter in the seventeenth and eighteenth centuries”, Journal for the history of astronomy , xix (1988), 239–55.

de Malvasia Cornelius Marquis , Ephemerides novissimae motuum coelestium … (Modena, 1662).

Chérubin Père D'Orleans , La dioptrique oculaire ou la theorique la positive et la mechanique de l'oculaire dioptrique (Paris, 1671).

Horrebow Peder O. , Basis astronomiae (Copenhagen, 1735), chap. 13, and quoted in Wolf, op. cit. (ref. 23), i, 172.

See Repsold J. A. , Zur Geschichte der astronomische Messwerkzeuge von Purbach bis Reichenbach, 1450 bis 1830 (Leipzig, 1908), and Wolf, op. cit. (ref. 23), i, 173–4.

William Pearson , An introduction to practical astronomy (2 vols, London, 1824, 1829), ii, 97.

Theodor Balthasar , Micrometria sive de micrometrorum telescopiis et microscopiis applicandorum varia structura (Erlangen, 1710).

Many of the micrometer screws studied had dimples in the end as a result of having been made on a screw lathe where the screw blank was supported by a dead centre. This was one of the chief sources of error of eccentricity in micrometer screws.

The instrument is actually signed “John Ronley” but there is little doubt that it was made by Rowley ( Bennett James A. , The divided circle (London, 1987), Fig. 58).

Price Derek J. , “The early observatory instruments of Trinity College Cambridge”, Annals of science , viii (1952), 1–12, pp. 11–12.

See Anthony Turner , Early scientific instruments: Europe 1400–1800 (London, 1987), Fig. 255.

LeFèvre , “Micromètre inventé par lui”, Machines et inventions approuvées par l'Académie des Sciences , i (1735), 103–5.

Père André Tacquet's Opera mathematica were published posthumously in Louvain in 1668, with Géometrie practique as the third part. A second edition appeared in 1707.

Maurice Daumas , Scientific instruments of the seventeenth and eighteenth centuries , transl. by Mary Holbrook (London and New York, 1972), 77–78.

Nicholas Bion Edmund Stone (trs.), The construction and principal uses of mathematical instruments … of N. Bion (London, 1758), 155–6.

1 line = 0.17473 inches ≈ 4.44mm but Bion used 1 line = inch ≈ 2.1mm.

Auzout , op. cit. (ref. 36), 6–10. For a discussion of errors caused by the calibration techniques, see Brooks , op. cit. (ref. 36).

de Duc Grandjean Fouchy , “Nouveau micromètre universel, inventé par M. Grandjean”, Machines et inventions approuvées par l'Académie des Sciences , vi (1735), 45–47.

Alan Stimson , “The influence of the Royal Observatory at Greenwich upon the design of 17^th & 18^th century angle-measuring instruments at sea”, Vistas in astronomy , xx (1976), 123–30, p. 128. The instrument is in the National Maritime Museum and has acquisition no. # S.27 and serial no. 727.

Gill , op. cit. (ref. 15), 249. Nicholas Horrebow , Dissertatio de novo micrometro (Copenhagen, 1735).

Bouguer was with the Académie des Sciences's 1735 expedition to Peru to determine the shape of the Earth by measuring a degree of longitude. His group was headed by LaCondamine and was complementary to Maupertuis's expedition to Lapland. Pierre Bouguer , “Mesure des diamètres des plus grandes planètes: Description d'un nouvel instrument qu'on peut nommer heliomètre …”, Mémoires de l'Académie des Sciences , 1748, 11–34; De LaLande J. J. , Astronomie (3 vols, Paris, 1792), ii, 639ff.

On longer instruments the screw was driven from the eyepiece end by a shaft with pinion gear turning a crown gear attached to the screw and dial.

James Short , “Letter concerning a paper of the late Servington Savery, Esq., relating to his invention of a new micrometer”, Philosophical transactions , xlviii (1735–54), 165–77.

Pézenas E. , a professor of hydrography at Marseilles, designed a heliometer-type micrometer and one was made in London (by Dollond?) c.1755 for the Observatoire de Marine de Marseille and was of 2-pied focus and mounted on a telescope of 40-pied focus. A second example was made for Pézenas in 1760 by Dollond but was of only 1-ft focus. ( Pézenas E. , “Description d'un nouveau micromètre appliqué à un telescope de réflexion, mêlée de recherches sur les micromètres et sur la manière de s'en servir”, Mémoires de mathématique et de physique redigés à l'Observatoire de Marseille , 1755–56, 93–97).

For a discussion on the centring of telescope optics see John Harris , Lexicon technicum (London, 1704) under “Optics”. Robert Smith ( A complete system of opticks (Cambridge, 1738)) also described George Graham's method but it was Harris's that Savery had used.

Short specifically used this term although saws of the day must have had difficulty cutting hard speculum metal and it is possible that rotating cutting discs charged with emery were used.

John Dollond , “An explanation of an instrument for measuring small angles”, Philosophical transactions , xlviii (1753–54), 551–64.

Brooks , op. cit. (ref. 2), Appendix E.

The achromatic lens was invented c. 1733 by Chester Moore Hall.

Pearson , op. cit. (ref. 41), ii, 180–1.

Pézenas , op. cit. (ref. 59).

Halley had used a micrometer with two sets of wires crossed at right angles in 1720–21 to make observations of the relative right ascensions and declinations of stars. The procedure was to orientate one star so that it ran along one of the wires and to determine the time between the passage of one star and a following star. The declination was found by determining the difference in time for the star to cross from one diagonal thread to the other (see Forbes E. G. , Greenwich Observatory: Origins and early history (1675–1835) (London, 1975), 81).

Smith , op. cit. (ref. 60), 347.

Smith and Bradley had worked together before becoming, respectively, Plumian Professor of Astronomy at Cambridge and Savilian Professor of Astronomy at Oxford, and of course Bradley became Astronomer Royal following Halley's death in 1742.

See Bennett , op. cit. (ref. 44), 118.

Maskelyne was Bradley's successor, but one, as Astronomer Royal and apparently found these directions in Bradley's handwriting and submitted them to Philosophical transactions for publication ( Maskelyne , op. cit. (ref. 33)).

Jacobo Johann Marinoni , De astronomica specula domestica et organico apparatu (Vienna, 1745).

Jesse Ramdsen , “Two new micrometers”, Philosophical transactions , lxix (1779), 419–31.

Indeed it may be argued that even the British makers were largely producing instruments that were requested by scientists, of which there were many more in London than in Germany.

Alto Brachner , G. F. Brander, 1713–1783 (Munich, 1983), 154–6.

John Smeaton , “Description of a new micrometer”, Philosophical transactions , xlviii (1753–54), 598–609.

Ibid. , 605–7.

Ibid. , 609.

John Smeaton , “Account of an observation of the right ascension and declination of Mercury”, Philosophical transactions , lxxvii (1787), 318–42.

Brooks G. P. Brooks R. C. (“The improbable progenitor”, Journal of the Royal Astronomical Society of Canada , lxxiii (1979), 1–23) provide a discussion of the accuracy of the ‘ear and eye’ method for determining transit times.

Ramsden , op. cit. (ref. 73), 419.

Charles Pierre LeMonnier , Histoire céleste (Paris, 1741), pp. lxxv ff.

Brooks R. C. , “M. de Chabert and the 1750 Louisbourg Observatory”, Journal of the Royal Astronomical Society of Canada , lxxiii (1979), 333–48, pp. 336–7.

William himself noted that he was experimenting with the designs for a number of micrometers and his letter to Alexander Aubert of 9 January 1782 suggests that Aubert was able to help solve the problem he had with coarse wires for his filar micrometers since Aubert sent him some “fine silver wire” (see Lubbock Constance A. , The Herschel chronicle (Cambridge, 1933), 102–4).

Alexander was the second oldest son, William the third oldest son and fourth oldest of the family.

Lubbock , op. cit. (ref. 84), 118–19.

Steavenson W. H. , “A peep into Herschel's workshop”, Transactions of the Optical Society (London), xxvi (1924–25), 210–20, p. 215. The lathe referred to in this passage is illustrated in Fig. 12 facing p. 221.

William Herschel , “Account of a comet”, Philosophical transactions , lxxi (1781), 492–501, pp. 500–1 and Pl. XXVI.

William Herschel , “Catalogue of double stars”, Philosophical transactions , lxxv (1785), 40–126.

Abraham Rees , Cyclopedia or universal dictionary of the arts, sciences and literature (London, 1819).

Lubbock , op. cit. (ref. 84), letter of 3 July 1782, 118–19.

See Robinson Henry W. Walter Adams (eds), The diary of Robert Hooke, 1672–1680 (London, 1935), for descriptions of Hooke's dealings with Tompion.

William Herschel , “Description of a lamp-micrometer and the method of using it”, Philosophical transactions , lxxii (1782), 163–72, pp. 164–5.

Q.v. William Pearson , “On the construction of a new position micrometer, depending on the doubly-refractive power of rock crystal”, Memoirs of the [Royal] Astronomical Society , i (1822), 65–81, Figs 5 and 6.

Forbes , op. cit. (ref. 67), 167–8.

Vol. i of Pearson , op. cit. (ref. 41), was published in 1824, vol. ii in 1829. Gill's contribution to the Encyclopaedia britannica , “Micrometer”, appears in vol. xvi which carries a publication date of 1878. However, Gill's article makes reference to a paper by Stone said to be in the December 1879 issue of the Memoirs of the RAS (it appears that the paper referred to is in fact Stone E. J. , “Extract of a letter to the Astronomer Royal”, Monthly notices of the Royal Astronomical Society , xxxix (1879), 433–4). The entry “Micrometer” in the eleventh edition of the Encyclopaedia britannica (London and Edinburgh, 1910–11), xviii, 381–90, was revised by Gill.

These categories were removed from the entry in the eleventh edition.

Troughton used an open ended U-frame to carry the webs while Dollond used a closed frame. The open frame was intended to keep slight tension on the web but the better closed design gradually won favour and was still being made in the U.S. after the First World War by the J. B. Lippincott Co. (see Louis Ball , The telescope (New York, 1922), 172).

Biot J. B. , Traité élémentaire d'astronomie physique (Paris, 1805). Republished with additions in 1810–11 and 1841–57.

David Brewster , Treatise on new philosophical instruments (Edinburgh, 1813), 7.

The wires of eighteenth-century micrometers were replaced by spider's webs c. 1800–10, micrometers with these being referred to as “spider's line” or “Troughton's micrometers”.

Pearson , op. cit. (ref. 41), ii, 101. Although this sounds incorrect, Pearson's intent was to make the easiest measurement and the one least affected by refraction. It is easier to measure the Sun's vertical diameter (despite the effect of refraction) rather than its horizontal diameter because the latter is affected by diurnal motion. However, the smallest refractive effect is in the summer when the Sun is relatively high in the sky and the amount of the refraction at high altitude angles was reasonably well-determined even in Pearson's time.

Q.v. James Ivory , “On the theory of astronomical refractions”, Philosophical transactions , cxxviii (1838), 169–229 (Bakerian Lecture).

Pearson , op. cit. (ref. 41), ii, 101–10.

The origin of this term is fairly obvious since micrometers were often used to measure the differences of right ascension of stars, and slack in the screw resulted in errors in right ascension and hence in the time.

German makers were also split as to which design to use: Vogler used a double spring while Hunaeus used a single spring ( Carl P. H. , “Die Scraube in ihren Anwendung auf physikalische, mathematische und astronomische Instrumente”, Repertorium für physikalische Technik für mathematische und astronomische Instrumentatkunde , ii (1867), 37–55).

The micrometer of Reichenbach's repeating circle at the Paris Observatory (c. 1811) is the earliest instrument that has been found with this type of anti-backlash spring.

A vertical circle in the Royal Observatory, Brussels, made in 1855 by Ertel, employs an eyepiece micrometer of this design. The scale micrometers on this and a companion vertical circle are of standard design and all have drums with 60 divisions.

Gill , op. cit. (ref. 15), 245.

Albert König , Die Fernrohre und Entfernungsmesser (Berlin, 1937), 141.

The pitch was normally ≈ 103.6 TPI. Those by Jones Thomas Robinson (of Devonshire Place, London) were apparently similar but those of Dollond were closer to 100 TPI (Pearson, op. cit. (ref. 41), ii, 100).

Repsold J. , “Neuer Vorschlag zur Vermeidung des persönlichen Zeit-Fehlers bei Durchgangs-Beobachtungen”, Astronomische Nachrichten , no. 2940 (1890), cols 177–82.

Repsold J. , “Durchgangs-Instrument mit Uhrbewegung”, Astronomische Nachrichten , no. 2828 (1888), cols 305–6. The concept was used on air sextants from c. 1920.

David Gill , A history and description of the Royal Observatory, Cape of Good Hope (Edinburgh, 1913), Pl. XIX.

Watts C. B. , “Experiments in the design of the travelling wire micrometer”, Astronomical journal , 1 (1944), 179–82, p. 179.

By 1911 Repsold was working on a micrometer which was to record the observation on paper in a manner similar in concept to the chronograph.

Warner Swasey received the contract for the telescope in 1892 and it was completed in 1897 (King, op. cit. (ref. 31), 316). Both men had previously been foremen at Pratt Whitney .

Browning (c. 1869–70) was one of the first to develop a micrometer for measuring spectral lines. These were based on his single screw model used on astronomical instruments.

Herrmann Dieter B. , The history of astronomy from Herschel to Hertzsprung (Cambridge, 1984), 163.

Robert Main , “On the present state of our knowledge of the parallax of the stars”, Memoirs of the Royal Astronomical Society , xii (1842), 1–60, and Monthly notices of the Royal Astronomical Society , v (1839–43), 51–56.

Q.v. King , op. cit. (ref. 31), 242–3. This instrument is in the Science Museum, London.

Hamilton J. A. , “Further considerations on the comparative observations of the differences …”, Transactions of the Irish Academy , xi (1810), 25–44.

Pearson , op. cit. (ref. 41), ii, 185.

Ibid. , 48.

Ibid. , 192.

Ibid. , 185ff.

Amici G. B. , “Descrizione d'un nuovo micrometro”, Memorie di mathematica e di fisica della Società Italiana (Modena), xvii (1815), 344–59.

Dawes W. R. , “On the measurement of the position angles of double stars, with the divided glass double image micrometer”, Monthly notices of the Royal Astronomical Society , xviii (1858), 58–59.

George Airy Sir , “On a new construction of the divided eye-glass double image micrometer”, Memoirs of the Royal Astronomical Society , xv (1846), 199–209. Brief descriptions also appear in Abstracts of the Monthly notices of the Royal Astronomical Society , vi (1843–45), 229–31 and Monthly notices of the Royal Astronomical Society , x (1848), 160. A description of the first form may be found in “On the principles and construction of achromatic eyepieces of telescopes and on the achromatism of microscopes”, Transactions of the Cambridge Philosophical Society , ii (1827), 227–52. The micrometer described by Airy in 1846 was an improved form.

Airy , op. cit. (ref. 129, 1846), 207–8.

Kaiser F. , “Untersuchung des airyschen Doppelbild-micrometers”, Annalen der Sternwarte (Leiden), iii (1872), 101–77 and 274.