Andrew Pritchard, 1804 - 1882

by Brian Stevenson
last updated February, 2017

Nota bene: this is a work in progress. There is much to say about Andrew Pritchard and his contributions to microscopy. This essay will be added to over the next several months. Significant changes will be highlighted on the menu bar to the left, as they develop.


Figure 1. Undated photograph of Andrew Pritchard and one of his microscopes. Adapted for nonprofit, educational purposes from the National Museum of Science and Industry (U.K.).

 

Andrew Pritchard’s Microscopes


Figure 2. Compound microscope, signed on the tube "Andrew Pritchard, 263 Strand, London", and on the foot, "Pritchard, Picket St., London". He traded from 18 Pickett St. between 1827 and 1835. Adapted for nonprofit, educational purposes from an internet auction site.

 

Microscope slides retailed by Andrew Pritchard

Andrew Pritchard probably had many better, more profitable things to do than make microscope slides. In addition to his optical retail business, he published books and journals, including a popular accounting of new patents. Although he was skilled in the manufacture of lenses, Pritchard is known to have outsourced lens production to Hugh Powell and Camille Nachet (Nuttall, 2006). He also brought in slides that were manufactured by Joseph Bourgogne, with whom he was friends (Figure 2). Therefore, one cannot assume that Pritchard’s name on an object means that he personally manufactured the item.


Figure 3. Microscope slides labeled with Pritchard’s name and address of 162 Fleet Street. It doubtful that he personally made any of them. Left, a circa 1840s dry-mount of Norfolk Island pine wood sections, comprised of two glass slips of the same thickness, sealed with yellow paper covering. Center, two circa 1850 slides by Joseph Bourgogne, the specimens mounted in balsam. Right, a standard-size (1x3 inch) balsam mount of guano diatoms, circa 1850s.

 





Figure 4. A boxed set of 16 microscope slides, sold by Andrew Pritchard, ca. 1840. The small slides are approximately 2 x 5/8 inches (5 x 1.6 cm). The case measures 2 1/4 x 1 1/4 x 7/8 inches (5.7 x 3.4 x 2.4 cm). Although it has been noted that some of Pritchard’s microscope books included lists of objects that could be cut out and used as slide labels, the printing on these slide’s labels does not mathc that in his books. The labels were most likely provided to the slide maker as printed sheets. All of the slides are dry-mounts, the coverslips are sheets of mica, and the glass is rough-cut.

 




Figure 5. A partial boxed set of microscope slides, sold by Andrew Pritchard, ca. 1840. The case is stamped with his name and address of 162 Fleet Street (lid is missing). The small slides are approximately 2 x 5/8 inches (5 x 1.6 cm). The case measures 2 1/4 x 1 1/4 x 7/8 inches (5.7 x 3.4 x 2.4 cm). All of the slides are dry-mounts, the coverslips are circles of mica, and the glass is rough-cut.

 





Figure 6. A two-shelf wooden cabinet of microscope slides, sold by Andrew Pritchard, ca. 1840. The lid bears an ivory label printed "Microscopic Cabinet", harkening to Pritchard’s 1832 book with that title. The small slides are approximately 2 x 5/8 inches (5 x 1.6 cm). The specimen labels are almost identical to those printed in Pritchard’s 1847 book, "Microscopic Objects". But the book’s list did not include "plumed gnat" or have exclamation points after specimen names, proving that the labels were not cut from that book. The coverslips are rectangles of mica, and the slides have papers covering the edges, a much finer finish than the slides in Figures 3 and 4.

 



Figure 7. (A and B) Front and back views, respectively, of microscope slides of wood sections prepared by “Mr. Darker’s method”, in both standard (1 x 3 inch) and the smaller continental size. These examples match those in Quekett’s 1852 list of Darker’s wood preparations (Figure 4). This type of slide is occasionally found with Andrew Pritchard’s name on a piece of paper between the two glass slips, indicating retail, but not necessarily manufacture, by Pritchard. (C) Edge view, showing the finely chamfered and polished edges and corners, and the groove where the glass slides meet, which facilitates penetration of the sealing wax for a strong bond. (D) Figure 214 from Quekett, 1852, described as “Two slides of equal size being selected the edges of each should be bevelled off on the metal plate as represented by fig. 214, so that when they are put together a groove or channel is formed, as shown at b in the figure.” This channel for the sealing wax is the most distinctive feature of Darker’s method, resulting in a strong bond between the glass slides. Earlier slide-makers did not grind wax channels, but instead applied sealing wax to straight-edged glass slips, forming a weaker, fragile bond between the glasses.

 

A type of microscope slide to which Pritchard’s name has become attached consist of two glass slides of the same size, the specimen(s) dry-mounted between, and the edges sealed with red wax (Figures 6 and 7). Such slides are occasionally found with Pritchard’s name printed on a slip of paper that is fixed between the glass slides. Pritchard also described production of such slides in his 1842 Microscopic Objects. These associations have led to a common perception that actually Pritchard made those slides. While it cannot be doubted that Pritchard retailed the slides that have his name attached, there are significant reasons to doubt that he made those or any of the other slides sealed with red wax.

John Quekett, an authority on microscopy, attributed the invention and production of the “red wax” slides to William Hill Darker (ca. 1811 - 1864). Darker was a renowned maker of microscope slides. His specialty was subjects for investigation under the polariscope, and all known “red wax” slides contain such items (e.g. wood sections). Quekett even described the distinctive method of the slides in Figures 6 and 7 as “Mr. Darker’s method”.

Quekett described “Mr. Darker’s method” of slide-making as, “Objects, such as sections of wood, that do not require a high power for their examination, may be mounted in a very neat way after an excellent plan first practised by Mr. Darker. The following description, abridged slightly from that given in a recent work, entitled Microscopic Objects, will convey a good idea of the method to be adopted for this purpose: ‘Two slides of equal size being selected the edges of each should be bevelled off on the metal plate … so that when they are put together a groove or channel is formed ... The surfaces having been cleaned, the bevelled parts are to be coated with a thin layer of sealing-wax varnish, when this is dry, a label, if required, may be gummed to the bottom slide, and then the objects laid on it; if it be necessary to keep them in place, the smallest possible quantity of gum may be applied to one corner; the top plate is now to be laid on the specimens, one of the edges is then to be heated in the flame of a spirit lamp, and the groove filled with sealing-wax, as shown at a; when one edge is done, the others are to be heated in the same manner, until the entire groove is filled with the wax, which thus acts two purposes, one to keep the slides together, and the other to prevent the access of air. The excess of wax may be cleaned off from the edges by rubbing them upon sand-paper laid on a flat board, until they are smooth; if bright edges be required, they may be passed quickly through the flame of the spirit lamp”. The author of Microscopic Objects, from whom Quekett borrowed the description of “Mr. Darker’s Method”, was Andrew Pritchard. However, even though Pritchard was astute at self-promotion and occasional truth-stretching, he never laid claim to the invention of using wax to seal microscope slides.

Third, Quekett’s 1852 and 1855 editions of A Practical Treatise on the Microscope, state, “Mr. Darker has long been known to microscopists for his skill in making sections of wood. From the time the achromatic microscope was first employed, he mounted sets of sections made in three different directions, between glasses, in the dry way, described in page 317 (i.e. Mr. Darker’s method). These served to illustrate the structure of the principal families of plants, and the popular as well as generic and specific names are printed on small labels, and introduced between the glasses”. This is followed by a list of common and Linnaean plant names, which correspond with known wax-sealed microscope slides of woods (Figure 8). Quekett also wrote, “The author, some years ago, was presented with a collection of sections of wood by Mr. Darker, which have not only kept in their places, but are as perfect and as free from confervae as when they were first received. They are all labelled after a very excellent plan, viz., by having the generic and specific name on one side of the label, and the popular on the other”. These comments from Quekett, and examples of such slides retailed by Pritchard (and datable by his shop addresses), indicate that Darker had been preparing slides with this method since the mid 1830s.


Figure 8. Two microscope slides attributable to William Darker, based on the handwriting and construction. The left is a lapidary mount of fossil palm wood, the right used “Mr. Darker’s method” to mount fresh sarsaparilla wood sections. Note the similarities of the word “Jamaica”.

 


Figure 9. List of preparations of woods produced for the microscope by William Hill Darker, from John Quekett’s 1852, second edition of A Practical Treatise on the Microscope, pages 403-405. “page 317” refers to “Mr. Darker’s method” of preparing microscope slides.


 

Pritchard Microscope Accessories


Figure 10. A section-cutting machine with knife (microtome), produced prior to 1835. Pritchard's name is engraved in the top surface. It was designed to cut thin slices of wood, for microscopic examination. One fits a piece of wood into the central hole, and the screw at the bottom allows incremental upward movements of the wood, which is then cut into slivers with the double-handled knife. The four holes in the top of the microtome are for fastening it to a table, for stability when cutting. Adapted for nonprofit, educational purposes from http://collection.sciencemuseum.org.uk/objects/co8040/early-microtome-england-1825-1835-microtome.

 


Figure. Andrew Prichard, 1843. Daguerreotype by A.F.J. Claudet.

 


Figure. Andrew Pritchard, circa 1855. Adapted for nonprofit, educational purposes.

 


Figure. Andrew Prichard, from a photograph dated June, 1869. Adapted from an internet auction site for nonprofit, educational purposes.

 

Acknowledgements

Many thanks to Howard Lynk, for his contributions to this and many other stories of early microscopists.

 

Resources

Bowerbank, J.S. (1870) Reminiscences of the early times of the achromatic microscope, The Monthly Microscopical Journal, 3:281-285

Bracegirdle, Brian (1998) Microscopical Mounts and Mounters, Quekett Microscopical Club, London, pages 77 and 108, plate 2

Davidson, B. (2009) John New and the introduction of Canada balsam into slide-making, Quekett Journal of Microscopy, 41:95-108

Falcon-Lang, H.J., D.M. Digrius (2014) Palaeobotany under the microscope: history of the invention and widespread adoption of the petrographic thin section technique, Quekett Journal of Microscopy, 42:253-280

Gould, C. (1829) The Companion to the Microscope, 6th edition, W. Cary, London

Nuttall, B. (2006) Marketing the achromatic microscope: Andrew Pritchard’s engiscope, Quekett Journal of Microscopy, 40:309-330

Pritchard, A. (1832) The Microscopic Cabinet, Whittaker, Treacher, and Arnot, London

Pritchard, A. (1842 and many other years) English Patents: Being a Register of all Those Granted for Inventions in the Arts, Manufactures, Chemistry, Agriculture, &c., Whittaker, London

Pritchard, A. (1847) Microscopic Objects, Whittaker and Co., London

Quekett, J. (1852) Practical Treatise on the Use of the Microscope, Second edition, H. Balliere, London

Quekett, J. (1855) Practical Treatise on the Use of the Microscope, Third edition, H. Balliere, London

Stevenson, B., and H. Lynk (2016) William Hill Darker, the Scientists’ Engineer, Quekett Journal of Microscopy, in press