Benjamin Martin, Pocket Microscope (signed by Dollond), ~1770-80

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The definition of a ‘field microscope’ is loosely referring to a sort of microscope that is intended to be portable, thus can be operated outside a laboratory. A ‘laboratory’ is currently defined as “a place where scientific research and development is conducted and analyses performed, in contrast with the field or factory” (Encyclopaedia Britannica, n.d.). However, this definition is rather modern. In the 17th and most of the 18th centuries, this term referred to alchemists’ workshops. Except for some unique cases, science laboratories sensu stricto did not exist before the beginning of the 19th century (Schmidgen 2011: 16-24). Moreover, to some extent, many of the 18th-century microscopes were portable in the sense that they could be folded or collapsed into a carrying case that could be transported with ease. Therefore, a better definition is needed for this term. 

The first dichotomy, already existing since the earliest days of the microscope, should be made between the ‘simple’ or ‘single’ and the ‘compound’ microscopes. By their nature and characterization, single microscopes were usually outfitted and designed to perform as portable, often pocket-sized devices. This generalization relates to most major categories of the 18th-century outlines, including the ‘acorn’ compendia of different shapes, ‘compass’, ‘screw-barrel’, ‘Ellis- aquatic’ and ‘botanical’ microscopes, and to specifically generic types such as the Lindsay, Watkins, Cuff, Withering, Clark, and Jones pocket microscopes.

The matter becomes more complex when the compound microscope is concerned. Looking at the 18th-century designs and later, although many microscopes were made to be packed in cases that technically could be carried away, they were never intended or designed to perform in the field. Thus, the fact that an instrument is portable does not necessarily turn it into a field apparatus. For the sake of discussion, we can distinguish between benchtop and handheld, with reference to the modern terms of desktop and portable as they concern personal computers. Between the second quarters of the 18th and the 19th centuries, such instruments were commonly labeled as ‘pocket microscopes’ although this designation was rather open-ended in technical terms. The best classification can thus be compound microscopes that were deliberately devised to be utilized in the open and were advertised as such.

It is perhaps Benjamin Martin himself who put the correct definition of his pocket microscope in the words of one of his imaginary figures in The Young Gentleman and Lady’s Philosophy follows (Martin 1772: 161-197). The two-volume book, intended to teach the principles of various fields of sciences to the broad public, is written in the form of a series of dialogues between an acknowledged Oxford College student named Cleonicus and his younger sister Euphrosyne. Home from his studies, Cleonicus is eager to share with his sister the advances of natural philosophy that he acquired in his academic studies. In his presentation of various kinds of microscopes, he refers to the pocket microscope. When Euphrosyne raises doubts whether a small microscope would do what a big one is capable of doing, Martin puts in her brother’s mouth the following answer: “In this you may, perhaps, be in some Degree mistaken: It does not follow, that the Field of View is always proportioned to the Largeness of the Instrument, or Glasses; there is a Mean in all Things, or Limits, which, as your HORACE tells you, are the Bounds of Perfection, on either Side of which it is impossible any Thing should be right. ---- You will wonder, perhaps, when I tell you, that a compound Microscope may be constructed not more than an Inch in Diameter, which will shew you most Sorts of Objects nearly as well as this large one of two Inches: And to convince you of this Truth, I have provided likewise a compound Microscope of a portable, or pocket Form, that you may take with you into the Gardens, or Fields, for instantly viewing any Object that may present itself in your Walk”. 

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There is no information about the absolute chronology of the various models of Pocket and “Drum” microscopes (Martin never used the latter term) along with his history as a producer of scientific instruments. Apparently, the first pocket microscope was produced during his Chichester residing period (Millburn 1976). The later improved shagreen over pasteboard ‘drum’ microscopes and the brass models belong to the London phase of his work (1756-1782). In 1766 Martin supplied scientific instruments to Harvard College (later to become Harvard University), after the fire that destroyed much of the scientific instruments of the college on January 24th, 1764. But the microscopes seem to have been bought from Adams and Nairne (Wheatland 1968: 179-188). Therefore, we cannot use this date as an anchor for absolute chronology regarding the models that he produced around this year. However, along the sequence of 26 years of production in London, there are few such anchors that can be used, mostly resulting from Martin’s dated sales catalogues and advertisements.

Turner (1981: 44-45) suggests a tentative date of about 1760 to the early form (lignum vitae, pasteboard, rayskin and brass) and about 1780 to the all-brass microscope from a compendium (Plate 3: 10, MHS 45432). However, this estimate seems to be too indiscriminating. Turner (ibid: 43) asserts that all these types but the first pocket microscope, which was first published in 1738 and the following years during his residence in Chichester, were produced during his period as an instrument maker in what became in due time his workshop at 173 Fleet Street, London. Martin started his London career in 1756 and maintained it till his death in February 1782. Therefore, the entire time frame of Martin’s production of drum microscopes lasted for 26 years. However, we don’t know if their product was maintained unceasingly along this entire sequence, and if their different models emerged along a unilineal evolutionary line, or whether there were several models that were introduced simultaneously. Undoubtedly, over this sequence, there must have been many more innovations and developments rather than the mere transfer from pasteboard and wood to brass. 

This phenomenon, of later models of Martin's microscopes bearing other makers' signatures, is most likely related to Martin's tragic death in 1782 and the events that followed.  Shortly after, his stock in trade was sold in an auction. The MHS copy of the auction sale catalog (Herring 1782), which lasted five days starting on March 8th, 1782, lists the instruments sold but not the buyers’ names. (The other list, with the buyers' names, was burnt completely due to the bombardments of Oxford in World War II). It indicates that the stock included about 40 microscopes of various types, of which there were seven compound or double microscopes of several kinds and several unfinished instruments. A few others were included in optical cabinets.

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The parallels to this 18th-century drum microscope are all related to Benjamin Martin, though most are unsigned. Most of the parallels to this microscope are found in the optical compendia made and advertised by Martin from about 1750 as a Cabinet of Optical Instruments. There, this microscope accompanies scioptic balls and telescopes. Therefore, while this specimen is signed 'Dollond London', ascribing it to John Dollond (1706-1761) or his son Peter, it should be related to Martin. There is no record showing that Dollond had ever produced any drum microscope before the end of the 18th century. Moreover, in the collection of the Science Museum London (SML), there is a Universal microscope, undoubtedly made by Martin but signed "P et J Dollond Londres", perhaps an instrument intended for export to France. Dollond is definitely known to have put his name on instruments recognizably made by other makers. Because this instrument has an "in-between" field lens after the Ramsden ocular, it is undoubtedly a later product made after 1759. 

It is logical to assume that much of the stock was purchased by the main retailers of these years, such as George Adams Jr., Peter Dollond, John, William, and Samuel Jones, etc. It makes much sense that these makers signed their names on the unsigned instruments that they bought and sold, to materialize their investment. Many items apparently passed to John Jones & Son (later W. & S. Jones of Holborn (Millburn 1986: 75), who advertised at least a dozen of Martin’s book titles in their catalogs. Millburn (ibid) indicates that many of the entries in their general sales catalogs of instruments between 1787 and 1795 were copied directly from Martin’s. This indicates that John Jones and his son William were major purchasers at the Martin sales. However, it is logical to assume that other major instrument makers of the time: Dollond, Adams, Nairne & Blunt, etc., also attended the auction and acquired unknown numbers of Martin’s instruments including some of his microscopes. Because Martin apparently did not sign many of his brass microscopes, it was possible for these later acquirers of his lot to sign his old drum microscopes.

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In 2014, I recorded Martin's brass pocket microscopes, and perhaps some later copies of them, in the Science Museum in London (SML), the Museum of the History of Science in Oxford (MHS) and the Whipple Museum in Cambridge. The above group photo, compiled from the photos of the instruments taken (with permits) in these museums, shows the variability in forms that occur. It seems that two of the instruments, Whipple 0588 and 1809, are not of Martin's make, but all the rest can be related with him. The slight variations reflect the habit of 18th-century makers to outsource the production of microscope parts between different workshops and only assemble them and retail under the signature of the formal maker. 

Provenance: previously in the collection of Dr. Patrick Bizouard (1933-2005), purchased from his son.​

References

Millburn, J., 1976. Benjamin Martin, Author, Instrument-Maker and 'Country Showman'. Leyden: Noordhoff International Publishing.Millburn, J., 1986b. Retailer of the Sciences, Benjamin Martin's Scientific Instrument Catalogues, 1756-1782. London: Vade-Mecum Press.

Similar instruments are in SML: 1925-148; A124818, 1911-295, 1928-919, A645009, (compendia by Benjamin Martin); Golub: 260 (unsigned compendium); Whipple: 588, 1809; Boerhaave: V07433; Clay & Court 1932, Fig. 128; Sotheby’s Dec 2006 cat. (signed B. Martin); Gemmary CD Cat. 23, 2004; Tesseract Cat. 95, 2012; Turner 1981: 44 (right); Skinner 1997: 91.