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Benjamin Martin, Pocket Microscope (signed by Dollond), ~1770-80
Benjamin Martin (attributed), Optical Cabinet, ~1780

The term 'field microscope' refers to a portable microscope that can be used outside of a laboratory. The definition of a laboratory has evolved over time and now refers to a place where scientific research and analysis are conducted. In the past, the term laboratory was used to describe alchemists' workshops, and science labs as we know them today were not established until the 19th century. 

The first classification of microscopes is between 'simple' or 'single' microscopes and 'compound' microscopes. Single microscopes were designed to be portable and could be pocket-sized. They included optical compendia of various shapes, as well as 'compass,' 'screw-barrel,' 'aquatic,' and 'botanical' microscopes. Specific types such as the Lindsay, Watkins, and Clark pocket microscopes were also included. 

Compound microscopes were more complex and were not designed to be used in the field, even if they could be transported in cases. Therefore, being portable does not necessarily make an instrument a field apparatus. Compound microscopes can be classified as either benchtop or handheld, similar to the modern terms of desktop and portable as they relate to personal computers. In the 18th and 19th centuries, microscopes designed for use in the open were commonly called 'pocket microscopes.' However, the best classification for field microscopes is compound microscopes that were intentionally designed and marketed for use outside of a laboratory.

In the book "The Young Gentleman and Lady's Philosophy" by Benjamin Martin, the character Cleonicus explains various types of microscopes to his sister Euphrosyne. When he mentions the pocket microscope, Euphrosyne questions whether a smaller microscope can do the same things as a larger one. In response, Cleonicus explains that the field of view is not always proportionate to the size of the instrument or glasses. He goes on to say that a compound microscope can be constructed to be as small as one inch in diameter and show objects almost as well as a larger microscope. To prove this point, Cleonicus provides a portable pocket microscope that can be used to view objects in the garden or field.

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Benjamin Martin (Gentleman's Magazine 1785)

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Martin's pocket microscope, second form, 1742

From: B. Martin, The Young Gentleman and Lady’s

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It is currently unknown when the various models of Pocket and "Drum" microscopes were produced by Martin, as well as the history of his work as a scientific instrument maker. The first pocket microscope was created while Martin lived in Chichester, and the improved shagreen over pasteboard "drum" microscopes and brass models were produced during his time in London from 1756 to 1782. In 1766, Martin supplied Harvard College with scientific instruments after the college's previous instruments were destroyed in a fire in 1764. However, it's unclear whether the microscopes were produced by Martin or purchased from Adams and Nairne. Therefore, this date cannot be used as an anchor for determining the absolute chronology of Martin's microscope models. However, there are a few anchors that can be used to determine the chronology of his microscope production during his 26 years in London, mostly from his dated sales catalogs and advertisements.

Turner (1981: 44-45) suggests that the early form of the microscope, made of lignum vitae, pasteboard, ray skin, and brass, dates back to around 1760. The all-brass microscope from a compendium, on the other hand, is estimated to have been made around 1780 (ibid: Plate 3: 10, MHS 45432). However, this estimate may not be accurate. Turner (ibid: 43) claims that all types of microscopes, except for the first pocket microscope, which was first published in 1738 and the following years during Martin's residence in Chichester, were produced during Martin's London career, which lasted from 1756 to his death in February 1782. This means that Martin's production of pocket microscopes lasted for 26 years. We don't know if their product was maintained throughout this period, if different models emerged along a unilineal evolutionary line, or if several models were introduced simultaneously.

It is evident that there were many more innovations and developments during this period, beyond the transition from pasteboard and wood to brass. The 18th-century drum microscope has several parallels related to Benjamin Martin, although most are unsigned. These parallels can be found in the optical compendia produced and advertised by Martin around 1750, called the Cabinet of Optical Instruments. This microscope was often accompanied by scioptic balls and telescopes. While this particular specimen is signed 'Dollond London', it is related to Martin as there is no record of the Dollonds producing any pocket microscope of this design before the end of the 18th century. In addition, the Science Museum London has a Universal microscope (SML 1925-148), undoubtedly made by Martin but signed "P et J Dollond Londres", possibly intended for export to France. It is known that Dollond put his name on instruments made by other manufacturers. The "in-between" field lens after the Ramsden ocular in this instrument suggests that it was produced after 1759.

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© Microscope History all rights reserved. All photos are by Y. Goren under written permission of the Science Museum London, the Museum of the History of Science, Oxford, and the Whipple Museum, Cambridge, and from the Goren Collection.

It is believed that later models of Martin's microscopes were signed by other makers due to Martin's tragic death in 1782 and the events that followed. After his death, his stock in trade was auctioned off. The auction sale catalog, which lasted for five days starting on March 8th, 1782 and is held by the MHS, lists the instruments sold but not the buyers' names. Unfortunately, the list with the buyers' names was destroyed during World War II due to the bombardments of Oxford. The auction catalog indicates that the stock included approximately 40 microscopes of various types, including seven compound or double microscopes of several kinds, several unfinished instruments, and a few others included in optical cabinets.

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It is logical to assume that during the 18th century, the main retailers such as George Adams Jr., Peter Dollond, John, William, and Samuel Jones purchased a significant amount of stock. They often signed their names on the unsigned instruments they bought and sold as a way to materialize their investment. A lot of these instruments were passed to John Jones & Son, who later became known as W. & S. Jones of Holborn. They advertised at least a dozen of Martin’s book titles in their catalogs and many of the entries in their 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 also reasonable to assume that other major instrument makers of the time, such as Dollond, Adams, Nairne & Blunt, attended the auction and acquired unknown numbers of Martin’s instruments, including some of his microscopes. As Martin apparently did not sign many of his brass microscopes, it was possible for these later acquirers to sign his old drum microscopes.

This phenomenon can be seen in the optical compendia such as the one from this collection, seen below. Several examples are known from other collections to be signed by W & S Jones, but the pocket microscope and the scioptic ball seem to be of Martin's production. These compendia were stored in rough mahogany cases and sold to the amateurish public.

In 2014, I conducted a study on Martin's pocket microscopes, and some copies of them, which are displayed at the Science Museum in London (SML), the Museum of the History of Science in Oxford (MHS), and the Whipple Museum in Cambridge. I took photographs of these instruments (with permits) in these museums and compiled them into a group photo, which shows the variability in forms that occur. It appears that two of the instruments, Whipple 0588 and 1809, are not made by Martin, but all the other instruments can be traced back to him. The slight variations reflect the 18th-century practice of outsourcing the production of microscope parts between different workshops and only assembling and retailing them under the signature of the formal maker.

Martin used to glue his sales catalogues to the inner side of the covers of some compendia. These catalogues may provide some valuable information, as noted by Millburn (1986b). Millburn sorted the catalogues by year (1757, 1765, 1780) and arranged them according to their lists of items. In the presented table, the microscopes are highlighted in yellow, and the original prices from the book were not included.

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Similar instruments are in SML: 1925-148; A124818, 1911-295, 1928-919, A645009, (compendia by Benjamin Martin); MHS 98894,  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.

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.

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