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Antoni van Leeuwenhoek’s Microscope

Giorgio Carboni, june 2012
Translated by Sarah Pogue

 


TABLE OF CONTENTS

Introduction
Operation
Construction
Adjustment
Illumination
Use
Conclusion
Bibliography

 


Figure 2 – Antoni van Leeuwenhoek microscope completed.
 


 

Introduction
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One of the first microscopes built by man was that constructed by the Dutchman Antoni van Leeuwenhoek (1632-1723). Despite the fact that he lacked a scientific background, using his own microscopes he succeeded in carrying out numerous and important observations in the field of microbiology. Throughout his life, Antoni dedicated himself to various crafts, including that of cloth merchant. In this trade, “pearls” of glass were used to examine the fibres of the cloth at a certain magnification in order to evaluate their quality. He realised that the smaller these pearls were, the more they magnified, and so he set about producing very small pearls: as small as 1 to 2 mm in diameter. During the creation of these tiny spheres he used increasingly finer abrasive powders. Another method used to produce these spheres was the fusion of pieces of glass. At high temperatures, the glass became fluid and the surface tension of the liquid gave the pieces of glass a very precise spherical form which was then maintained when they cooled. The handling of these small lenses was very difficult however and the instrument that van Leeuwenhoek developed served to bring the samples to be observed within a few tenths of millimetres of the surface of the lens.

The telescope was invented at the beginning of the 1600s and thanks to Galileo Galilei, who pointed it towards the night sky to observe the Moon, Jupiter and Venus this instrument gained immediate fame. In fact, the astronomical observations that were made possible by the telescope allowed humanity to make remarkable advances in understanding the cosmos. The telescope also gave us the possibility to observe a distant ship and to understand if it was a friendly or hostile vessel in time to escape or to prepare for battle.

The microscope came into being at more or less the same time as the telescope, but it did not share the same fortune. In fact, for a number of decades it was considered more a toy than a scientific instrument. It was only after much time that the importance of the microscope in understanding biological phenomena, in curing diseases which up to then had been fatal, and in many other applications was recognized.

In the second half of the seventeenth century Robert Hooke was active among numerous other makers and users of microscopes. This important character in microscopy discovered, amongst other things, the cells. Hooke used mainly compound microscopes, but also used simpler microscopes similar to those of van Leeuwenhoek. In optics, a “simple microscope” is a microscope formed of a single lens and a “compound microscope" is a microscope formed of more than one lens (objective and eyepiece). The first compound microscopes were obtained by turning a telescope upside-down, but they had limited magnification. You should not think that the invention and perfection of the microscope were achieved by a single individual, as there have been many tens of protagonists in the story of the microscope who supplied innovations which, over the course of several centuries, led to the creation of the instrument as we know it today and of its different variations. Amongst the most important contributions to the perfection of the microscope are those of Galileo Galilei, Christian Huygens, Marcello Malpighi, Robert Hooke and Johannes Kepler.

It appears, however, that the compound microscopes of that period were of inferior quality when compared to the simple microscopes. If you also build Hooke’s microscope, which I have described in another article in this gallery, you can make comparisons and thus form your own opinion. The construction of van Leeuwenhoek’s microscope can, amongst other things, give you an idea of the not insignificant difficulties which its users had to overcome in order to carry out their observations. You can see for yourselves how van Leeuwenhoek saw with his instruments. Obviously, you can also use this microscope to carry out naturalistic observations.


Operation
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Before we occupy ourselves with the details of building this instrument, it is a good idea to give a brief description of it. The use of a spherical flask filled with water to magnify the image of an object was known since ancient times. Nobody, however, had the idea to use this to observe natural phenomena. As I have said, Antoni realized that the smaller the sphere, the greater its magnifying capabilities. Thus, he set about producing very small spherical and biconvex lenses (some less than 2 mm in diameter). He also realized that the smaller the sphere, the more difficult it was to handle. In order to conveniently use these small lenses, he had to construct an instrument with which he could regulate the distance of the sample from the objective, with the precision of just a few tenths of a millimetre. The sphere was placed between two sheets of brass in a specially-made fitting (see figure 1, indicated by the red arrow). A few screws allowed him to focus the image and in certain cases to obtain reasonably clear images. The use of this instrument soon revealed itself to be rather laborious, so much so that apart from him only a very small number of people managed to use it. The sample to be observed was placed on the point of a specimen pin situated immediately to the left of the objective (figure 1). The main screw serves to move this point up and down. The screw at the bottom right allows the pin to move to the right and left and also serves to block it.


Construction
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In the construction of this instrument, I used materials different to those found in the original for some of the components, and in particular I used aluminium in place of brass. However, these are supporting components which have no influence on the optics. In any case, the aim of the exercise is not to construct an exact replica of the van Leeuwenhoek instrument as a collector’s item, but to construct a microscope that functions in a similar way to that of the famous inventor and which allows us to have a more precise idea of how he saw the organisms that he drew. Therefore, this project can be considered experimental archaeology, where ancient instruments are reproduced so that we can use them and by doing so understand how they were utilized, what advantages they conferred etc.

You can therefore change the dimensions and materials of the various parts, as long as you try to keep them as close as possible to the original near the objective. In the preparation of the specimen pins and the liquid specimen holder, remember that figure 1 is misleading. In fact, the sample should not be positioned as far from the objective as shown in the diagram. In figure 1, this distance is several millimetres, while it should really be only a few tenths of a millimetre. The measurements that I give relate to my microscope (figure 2), which you will have to adapt them to your instrument.

 

Objective
Let’s begin with the construction of the objective (figure 3). In order to do this, you will need to procure a Bunsen burner, a gas camping cylinder, a flow regulator and a tube. In place of the Bunsen burner and its associated equipment, you could use a gas torch. Carry out the construction in the open air. You will also need some glass rods approximately 5 mm in diameter, a pair of tweezers and some small boxes to gather the objectives you produce. Some of these items can be purchased in a hardware store, others in a chemical supply store.

To reduce the formation of bubbles in the glass spheres, wash the glass rod well using soap and water and then don’t touch it anymore in the central part. After turning on the Bunsen burner and regulating the flame so that it is oxidizing, heat the central part of the glass rod whilst turning it with your fingers. When the glass has softened sufficiently, remove the rod from the flame and pull the two extremities apart until you obtain a thin strand of glass approximately 0.3 mm in diameter. Using the tweezers, break the strand in half, taking care not to touch it with your fingers. Bring one of the strands obtained to the side of the flame and move it closer until it begins to melt, forming a ball. Allow this sphere to grow by approaching the glass strand closer to the flame, until it reaches a size of 1.5-2 mm, then remove it from the flame and leave the sphere to cool. Break the strand as close as possible to the sphere. The surface tension of the melted glass guarantees the spherical shape of the sphere. However, the force of gravity tends to deform the sphere, therefore, to obtain good quality objectives, the spheres should be small in size. You will need to prepare at least a dozen spheres and then, with a fairly powerful lens, choose one that is of the correct dimensions and free of air bubbles and other imperfections. This will be the microscope’s objective. Keep the other good quality lenses as reserves.

High quality glass spheres can be purchased from the American company "Edmund" (fused silica balls). If you have an old microscope objective to sacrifice, remove all of the lenses other than the last (the closer with respect to the sample). This should be hemispherical.

 

Body-plates
Next, we will move onto the plates and to the fitting that will house the objective, see figures 1 and 4.
The objective is placed between two brass plates 0.5 mm thick, 38 mm wide and 70 mm long.

Make holes for 2 mm rivets (see figure 1), but for the moment use screws 2 mm in diameter and tighten the relative nuts. With a 1 mm diameter drill bit and in line with the fitting for the objective, make a hole which passes through both plates. In the plate closest to the eye (indicated by the red arrow in figure 2), widen the hole to 1.2 mm.

Using a burin with a conical point at 90°, make the fitting for the sphere on both sides. To facilitate this operation, it is convenient to anneal the plates in these points to make the material easier to work. At the end of the operation, the sphere should not rattle in its fitting.

With a file, smooth the external part of the fitting so that it is possible to bring the sample within 0.1 mm of the lens. Be careful when using the file so that you do not touch the lens with it. Remove the objective from its seat before using the file!

If the sphere can stick out of a couple of tenths of a millimetre from the sample side, is better. Trim the holes of the fitting for the objective. Figure 4 gives the sizes that allow you to better understand how to construct this fitting.

Separate the plates, clean them and spray the interior of the two fittings with black opaque paint.
With the aid of a watchmaker’s lens or better still a stereoscopic microscope, verify that the lens is held still in its fitting and that is orientated in such a way that the attachment point of the glass strand does not correspond with the holes.
With some 2 mm diameter aluminium bonsai wire or with some 1.5 mm diameter electrical copper wire, make the rivets. The aluminium rivets are very soft. Remove the screws one at a time and mount the rivets (the sphere should already be in position).

 

Figure 5 – Specimen holder for liquid samples. Note also
the hole in the block at the extremity of the main screw
which is rendered elastic using a lateral cut.

Figure 6 – Blocking screw of the main screw.

Figure 7 – Blocking screw and the main screw.
A nut is soldered onto the lower plate.

 

The block
The block is moved forwards and backwards by the main screw. It is moved to the right and to the left by means of arcs of circle around the blocking screw.
On the block a normal specimen pin or a liquid specimen holder is mounted (figure 5). These points must graze the objective.
In figure 5, the hole on which the main screw works is visible, whose thread is removed for the last 6 mm.
The hole in the block is adjustable in such a way as to be able to reduce the strokes that would make the pins instable. This device is not present in the van Leeuwenhoek’s microscopes, and you could do without it if you so wish.
On the other side of the block, a focussing screw is visible (of little use because it goes immediately out of focus). My block has the following sizes: 8 x 16 x 32 mm.
Low down on the block make a threaded hole in which to insert the pins (one at a time). This hole should be a little inclined so as to be directed towards the objective (without touching it).

The bracket
Cut a length of L-shaped metal, or bend a plate of brass or aluminium to form an angle of 90°, to support the main screw.
Make a threaded hole in this piece of metal and mount the main screw. In figures 6 and 7 the blocking screw of the main screw is visible.
Bend the piece of metal so that the block scrapes lightly against the plate.

The main screw
To make the main screw, a headless screw or a 70 mm long piece of threaded M6 brass insert will suffice.
At one end fix a little plate or a pin to manoeuvre it.
At the other end reduce the diameter of the screw to 4.2 mm x 6 mm.

As you can see in figure 5, make a hole in the block using a 4.2 mm point.
Make a lateral incision and use a socket head screw to regulate the diameter of the hole.
The instrument is also equipped with sample holders to observe liquid samples.

Focussing mechanism
In figure 1 a screw is indicated which constitutes the focussing mechanism that allows you to regulate the distance of the pin from the objective. In reality, if you maintain the proportions depicted in figure 1, you would not be able to see anything. In fact, in that figure, the distance between the point and the objective is a few millimetres (and it can only move further away), while it should be a few tenths of a millimetre away. In practice this screw also reveals itself to be of little use because it is more than often necessary to move the pin closer to the objective rather than further away. In order to focus it is often necessary to press on the pin or to flex the plates to approach them closer to the objective.

Specimen holders
For this microscope, specimen pins and liquid specimen holders are useful. All of these pins can be inserted in a custom-made M3 hole in the block.
The specimen pins serve to support samples with a creamy consistency. The liquid specimens serve to support samples with a liquid consistency.

Prepare some brass rings with an internal diameter of 6 mm, an external diameter of 8 mm and 1 mm thick. Using a glass cutter and a circular template, cut some 8 mm discs from coverslips.
Weld a metal ring to one end of a headless M3 screw (figure 5). Using a stick, press the ring onto the plate. As a result, the ring should be parallel to the plate and should graze it.
Using silicone or another type of glue, secure a glass disc which you obtained from coverslip. You will obtain specimen holders which serve to hold liquid samples.
As material for the transparent discs and following in the footsteps of van Leeuwenhoek, you can also use thin sheets of mica.
On the holders it is useful to fix a nail so that you can press on the holder without touching the sample.


Adjustment
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Mount and adapt the various parts. Tighten the elastic hole on the main screw (figure 5) to reduce the stroke. Position the specimen pin in line with the objective.
This microscope is not equipped with all the necessary movements, but instead is largely based on the pressure and traction exerted on some of its parts, on the pins and the plates for example. Make a few attempts at observation by placing a sample on the specimen pin. Substitute the pin and mount a ring specimen holder. Place a drop of pond water in the holder and centre the ring with respect to the objective. Whilst making adjustments by pushing or pulling the specimen holders, it is easy to ruin the sample and dirty your hands. To avoid this, weld a peg onto the specimen pins and liquid holders so that your fingers are always a certain distance from the sample. Keep the optic of this little microscope clean as it is essential to have clear images.


Illumination
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For this instrument, illumination is particularly important. Unfortunately, we do not know which system van Leeuwenhoek used. Sunlight, both direct and reflected by a mirror, must be discarded as an option because it is too strong and comes from a solid angle that is too limited. He could have used candlelight, or the flame from a gas lamp concentrated by means of a spherical flask filled with water and perhaps used in conjunction with a semi-spherical lens. In this way, he could have illuminated the sample using reflected light (episcopic). With the liquid specimen holders he could have obtained illumination by transparency (diascopic). You can experiment using techniques and materials available in van Leeuwenhoek’s time. To make your life easier, try using an electric lamp with a frosted bulb placed at a distance of approximately 30 cm. If you keep the light source too close to the microscope, you won’t be able to see anything. You will have to find the correct distance by trial and error. If you are too close, you will find yourself in the same situation as a microscope with the diaphragm completely open and you won’t be able to even discern the sample. If you are too far away, the images become too contrasted and lacking in fine detail.


Use
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When observing creamy or solid samples, use specimen pins. In this case, the microscope can be kept in the upright position and the observer’s eye must look in the direction indicated by the red arrow in figure 1. When observing liquid samples, for example pond water, you must use a liquid specimen holder. In this case, the microscope must be positioned horizontally so that the water does not flow away but is distributed in a reasonably uniform manner inside the ring. The sample is placed at a distance of a few tenths of a millimetre from the small sphere (for a glass sphere with a diameter of 2 mm, this distance should be 0.47 mm or approximately half a millimetre, which becomes 0.3 mm when you consider the thickness of the glass disc). The eye must be positioned as close as possible to the sphere (at a distance of a few centimetres).

For the first observations, mount a specimen pin. Position a sample, some mould for example, on the pin and observe. Repeat this with other samples, and try to observe the microorganisms present in pond water, taking a sample by scraping material from small greenish sticks or stones. With a dropper, place a drop of water on the glass of a liquid specimen holder. To prevent the water from spilling, keep the instrument in a horizontal position. Don’t place too much water or too much detritus in the holder. Always look in the direction indicated by the red arrow in figure 1.

If you are able to see something this means that you have brilliantly overcome many challenges in optics and mechanics! Very few people amongst those who tried the original microscopes of van Leeuwenhoek succeeded in seeing something. Therefore, continue to make observations so that you will have practice using the instrument and be able to improve your results.


Conclusion
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As I have said, this instrument will allow you to carry out observations in a manner very similar to that of van Leeuwenhoek and to understand the difficulties with which he had to struggle for many years. It will also permit you to make comparisons with compound microscopes with glass-sphere objectives. The construction of this ancient instrument allows you to comprehend the importance of certain details in producing a functioning model. For example, it makes you understand the importance of having a clean objective, of placing the sample under observation very close to the objective and of positioning the microscope at a certain distance from the light source to be able to discern the sample. You should also continue making attempts to improve the instrument. If you so wish, you could move onto other models of microscope that use glass spheres and introduce important improvements, which are also described in this gallery.

The completion of this instrument, with all of its demands, will fill you with wonder at all of the mechanical operations that van Leeuwenhoek knew of and carried out in the XVII century, such as making and threading the various holes, cutting and filing the plates and the block, making very small perforations in the seat of the objective, soldering certain elements, producing the objectives, cutting glass discs only a few millimetres in diameter, in other words: our compliments Mr Leeuwenhoek!


Bibliography
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1 - http://www.vanleeuwenhoek.com/ Thonis van Philipszoon "Antonj van Leeuwenhoek" 1632 - 1723 A.D.
2 - Antonj van Leeuwenhoek, Father of Microbiology History of Antonj van Leeuwenhoek, with his microscopy methods and discoveries
     A large quantity of useful information.
3 - http://www.juliantrubin.com/bigten/leeuwenhoek_microscope.html Repeat Famous Experiments and Inventions.
     Hands On Activity: Build a van Leeuwenhoek Microscope ***
4 - http://www.funsci.com/fun3_en/usph/usph.htm A glass-sphere microscope.
5 - http://www.microscopy-uk.org.uk/mag//artapr07/hl-scope.html Making a Van Leeuwenhoek Microscope Lens
6 - http://www.mindspring.com/~alshinn/Leeuwenhoekplans.html To Make a Van Leeuwenhoek Microscope Replica

Internet keywords: Leeuwenhoek, Hooke, microscope, lens, glass sphere.

7 - C.L. Stong; from: "The Scientific American; Book of projects for the amateur scientist"; 1960; Simon and Schuster Inc. New York
     It is a collection of articles wrote by different authors, devoted to the amateur scientist and edited by C.L. Stong.
8 - Roger Hayward (1899-1979), artist, architect, designer of optical instruments, astronomer.
9 - Turner, Gerard, L'Estrange . Collecting Microscopes. London, A Studio Vista Book published by Cassell Ltd. 1981, cm.20x25, pp.120.

 


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