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Thoughts on Van Leeuwenhoek’s optical tool box

My personal project to find the descriptions of methods buried in Van Leeuwenhoek’s letters and to try and work out how he did things that he didn’t describe continues. My most recent results have now appeared in the Nov 2017 FEMS Letters with the POI: https://doi.org/10.1093/femsle/fnx247. The paper covers problems encountered with using the classical microscopes with some samples that we know he studied, and suggests a solution.

Antoni van Leeuwenhoek did not limit his research to microorganisms. Indeed, he worked with a very wide range of samples ranging from wood and animal tissues through insects to individual cells and sperm to bacteria. His microscopes work very well with transparent samples where the light can pass through them (and the samples were small) but, as can be seen from Figure 1, he was obviously also using reflected light.

Transmitted and reflected lighting of a gnat

Figure 1A shows a drawing of a gnat, taken from a 1702 Van Leeuwenhoek letter. Figures 1B and C. show a similar insect photographed under a 19th century Carl Zeiss Jena microscope with transmitted (B) and reflected (C) light. It is clear that the level of detail shown by Van Leeuwenhoek cannot be observed on the silhouette shown in B.

The details are all in my papers, but my conclusion is that, as he did with his aalkijkers (his microscopes for viewing the blood in the capillaries of the tails of small eels and fish where the sample pin was replaced by a glass tube to keep the specimen alive), Van Leeuwenhoek adapted his magnifiers to suit the task in hand.

Figure 2 shows a collection of magnifying equipment that I think Van Leeuwenhoek used as his optical tookbox. The photographs show modern facsimiles, the drawings were made during or just after Van Leeuwenhoek’s life. This conclusion is based on experimental results and historical documents.

Figure 2: Optical toolbox

A: This magnifying glass (or something very like it) appears in the frontispiece of the auction catalogue for the sale of Van Leeuwenhoek’s microscopes after his daughter’s death. Because the lens is set into a simple ring rather than the metal plate of the Van Leeuwenhoek microscope, the setting does not cast a shadow on the sample if reflected lighting is used.

B: This version of the Van Leeuwenhoek microscope was published by a German visitor (Zacharius-Conrad von Uffenbach), and microscopes with 2 lenses are mentioned in the sale catalogue. With 2 different lenses side by side, it would have been more convenient than moving a fragile sample to another microscope for a different magnification.

C: This 3-lensed microscope comes from an engraving made while Van Leeuwenhoek was in the prime of life, and is also mentioned in the catalogue. Note the holder for a capillary (used for liquid samples such as blood) beside the sample needle.

D and F: Copies of 17/18th century magnifying glasses, as sold by the Rijksmuseum Boerhaave. “Burning glasses” are mentioned in the inventory of the Van Leeuwenhoek house after Maria van Leeuwenhoek’s death. As well as magnifying larger samples, they can be used to control the lighting of samples on the microscopes.

E: Some of the facsimiles of existing Van Leeuwenhoek microscopes made by Hans Loncke and used in my experiments.

G: Van Leeuwenhoek’s adaption of the eyepiece on his aalkijker to allow reflected lighting while protecting the eye with a small cup.

H: A facsimile of the aalkijker drawn in Van Leeuwenhoek’s first paper on blood circulation. Note the use of the same lens plate as with the microscopes.

I:  His final adaption of the aalkijker to make its use easier for visitors, as mentioned by him in a letter and drawn by Von Uffenbach.

People often describe his microscopes as crude, and perhaps they are when compared to other, ornamented microscopes of his time, but I suspect that Antoni van Leeuwenhoek was more interested in making something that would allow him to carry out his experiments rather than producing elegant instruments.

Exploring the Delft School’s microscope collection – 1.

As I have mentioned before, the Delft School of Microbiology Archive has a small collection of old and unusual microscopes. We also have a range of attachments with varying (and sometimes unidentified) functions as well as two boxes of mysterious parts. One of my projects for this winter is to try as many of these things out as possible, and write a methods book for the collection.

I have started with two red boxes from Ernst Abbe’s time at Carl Zeiss Jena (CZJ). Abbe was one of the founding fathers of CZJ and the inventor of many microscope techniques that we take for granted today, including standardizing  lens quality. One of the boxes contains the parts necessary to convert a simple microscope for work with polarization, the other contains a camera lucida. Both were obviously routinely used in the times of Beijerinck, Van Iterson and Kluyver and we have enough of each for every student in a practical class to use them. None of the boxes included instructions, and nobody I’ve asked had tried to use either one. Since they turn up sometimes on auction sites, it seems to be worth outlining my findings here. I used my late 19th century jug-handled CZJ microscope.

 

The polarizer.

The box contains a polarizer (top right in the photo), a calibrated ring (centre) and an eyepiece (bottom left). It took me a while to realize that the polarizer is actually two pieces which unscrew. The piece with the lens fits into the filter ring under the condenser, and the ring screws on underneath the filter ring to stabilize the polarizer. The calibrated ring fits around, and the eyepiece over the ocular.

The contents of the polarizer box.

Using my usual LED lamp, I adjusted the mirror and condenser to give optimum light and then inserted a slide. Rather than microorganisms, for these experiments it was simpler to use samples guaranteed to give the dramatic colour changes associated with polarizing microscopy and so I chose mineral samples prepared for the microscope by Dr F Krantz of Bonn around the beginning of the 20th century (and also in our collection). The pairs of photos show the extremes of uncrossed and crossed polarized light paths for 3 different minerals.

 

The camera lucida

The box contains a ring which fits over the microscope’s ocular. Attached to the ring is an arm with a mirror at its end and a shorter, moveable arm supporting the prism that combines the images from the microscope and the mirror. The arm allows the prism to swing over or away from the ocular, allowing the microscope to be used with and without it (very useful for focusing and sample placing).

Initially, I found this attachment very frustrating because everyone I had discussed it with confidently said that it projected the sample’s image onto paper beside the microscope. This did not happen. It was only when I looked through the ocular to check the microscope’s focus and saw a ghostly pen superimposed on the sample that I realised that the projection was the other way round! Thus far, I am not very satisfied with my photographs of the combined images, but I’ll post a picture here when I’m happy with them. The problem is not in using the equipment, but in convincing the camera that it can focus on the pen and sample at the same time – I see that CZJ’s catalogues of the time also offer a drawing platform for use with their camera lucida which was presumably exactly the correct height. If anyone wants to try, I’ve had better results with cream coloured paper rather than bright white paper which tends to reflect more in the field of view. Reducing the light in the room also helps.

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