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Grinding the glass

Although a mold can be pressed onto a turning piece of glass, it is more likely that van Leeuwenhoek used a foot treadle to turn the mold and then pressed the glass into it.

The photo shows a vertical lathe but van Leeuwenhoek probably used a horizontal lathe.

Van Leeuwenhoek's Lenses

Although we don't know for certain, it seems reasonable that van Leeuwenhoek knew of Hooke's Micrographia and that he at least saw if not looked through microscopes like Hooke's using two or three lenses. If so, then he knew their limitations, the chromatic and spherical aberration, the difficulty of illumination, the magnification of, at best, around ten or twenty times, the resolution in millimeters, not microns.

Perhaps van Leeuwenhoek used some of these microscopes for observations that did not require high powers of magnification. However, all the evidence we have indicates that van Leeuwenhoek used only one basic microscope design and one kind of lens, convex on both sides.

Van Leeuwenhoek made his own microscopes, hundreds of them, using a lathe and metal sheets and rods and ordinary soda-lime glass.

Unfortunately, only nine of his microscopes have survived. We do not know how representative they are of all of his microscopes. And we do not know which microscopes were used for which discoveries.

Telescopes, of course, need large lenses; the larger the better. For van Leeuwenhoek's microscopes, however, the smaller the lens, the greater the magnification. While it was more difficult to use, van Leeuwenhoek's simple microscope magnified at higher powers and with better resolution than Hooke's compound microscope. Not just incrementally better, but an order of magnitude better.

Of the surviving Leeuwenhoek lenses, the best, that is, the smallest, is now in Utrecht. It is a slightly aspherical glass bead under 1.5 mm in diameter and has a focal length slightly under a millimeter. The aperture stops the lens down to 0.7 mm, which reduces the spherical aberration. It magnifies 266 times to a resolution of about 1.3 um.

In fact, compound microscopes did not reach the performance of van Leeuwenhoek's single lenses until the mid-1800's. Van Leeuwenhoek's simple lens gave him a tremendous competitive advantage.

Van Leeuwenhoek had three methods for making his lenses:

bulletgrind a piece of glass until it is smooth and uniformly curved

bulletblow a tube with a closed end and shape the tip

bulletmelt a sphere by twirling a glass whisker in a flame

Many consequential discoveries and developements in science and engineering were made by the inventors of the tools with which the discoveries were made. Not only Leeuwenhoek, but his contemporaries Galileo, Newton, Hooke.

Robert Thom painting of van Leeuwenhoek at work

In the 1950's, U.S. artist Robert Thom was commissioned by pharmaceutical manufacturer Parke-Davis for a series of 45 oil paintings depicting the history of medicine. The collection was published in book form and widely distributed to new medical doctors. The painting was doneRobert Thom in the style of Vermeer and shows van Leeuwenhoek holding his tiny lens up to the daylight. The tools of his research are on the table. The linen and ribbons he sold in his shop are on the bench on the left.

Hooke's microscope

The first illustration, drawn by Robert Hooke, in his Micrographia (1665). He described it (emphasis added):

"The Microscope, which for the most part I made use of, was shap'd much like that in the sixth Figure of the first Scheme, the Tube being for the most part not above six or seven inches long, though, by reason it had four Drawers, it could very much be lengthened, as occasion required; this was contriv'd with three Glasses; a small Object Glass at A, a thinner Eye Glass about B, and a very deep one about C:

"This I made use of only when I had occasion to see much of an Object at once; the middle Glass conveying a very great company of radiating Pencils, which would go another way, and throwing them upon the deep Eye Glass. But when ever I had occasion to examine the small parts of a Body more accurately, I took out the middle Glass, and only made use of one Eye Glass with the Object Glass. ...

"My way for fixing both the Glass and Object to the Pedestal most conveniently was thus: Upon one side of a round Pedestal AB, in the sixth Figure of the first Scheme, was fixt a small Pillar CC, on this was fitted a small Iron Arm D, which could be mov'd up and down, and fixt in any part of the Pillar, by means of a small Screw E; on the end of this Arm was a small Ball fitted into a kind of socket F, made in the side of the Brass Ring G, through which the small end of the Tube was screw'd; by means of which contrivance I could place and fix the Tube in what posture I desir'd (which for many Observations was exceeding necessary) and adjusten it most exactly to any Object.

"For placing the Object, I made this contrivance; upon the end of a small brass Link or Staple HH, I so fastned a round Plate II, that it might be turn'd round upon its Center K, and going pretty stiff, would stand fixt in any posture it was set; on the side of this was fixt a small Pillar P, about three quarters of an inch high, and through the top of this was thrust a small Iron pin M, whose top just stood over the Center of the Plate;

"O n this top I fixt a small Object, and by means of these contrivances I was able to turn it into all kind of positions, both to my Eye and the Light; for by moving round the small Plate on its center, could move it one way, and by turning the Pin M, I could move it another way, and this without stirring the Glass at all, or at least but very little; the Plate likewise I could move to and fro to any part of the Pedestal (which in many cases was very convenient) and fix it also in any Position, by means of a Nut N, which was screw'd on upon the lower part of the Pillar CC. All the other Contrivances are obvious enough from the draught, and will need no description."

Cock's microscope

Johannes Faber, fellow of the Accademia dei Lincei, gave the name "microscopio" (microscope) to Galileo's "occhialino" (small eyeglass) in 1625.

These microscopes were designed and used by Robert Hooke and made by Christopher Cock, London, around 1665. The main tube of the microscope on the right is 7 inches long and 4 inches in diameter, made of leather-covered cardboard. The brass rod it slid up and down on is 15 inches high.

Using Kepler's design, these microscopes had in addition a field lens mounted close to the eyepiece lenses to widen the field of view. It was focused by moving the tube, not the specimen.




Hooke's illumination system

Hooke used a liquid-filled globe to project the light onto the specimen from the sun or an oil lamp (shown here with oil supply far left). He wrote in Micrographia (1665) (emphasis added):

"First, for Microscopes (where the Object we view is near and within our power) the best way of making it appear bright in the Glass, is to cast a great quantity of light on it by means of convex glasses, for thereby, though the aperture be very small, yet there will throng in through it such multitudes, that an Object will by this means indure to be magnifi'd as much again as it would be without it. The way for doing which is this.

"I make choice of some Room that has only one window open to the South, and at about three or four foot distance from this Window, on a Table, I place my Microscope, and then so place either a round Globe of Water, or a very deep clear plano convex Glass (whose convex side is turn'd towards the Window) that there is a great quantity of Rayes collected and thrown upon the Object: Or if the Sun shine, I place a small piece of oyly Paper very near the Object, between that and the light; then with a good large Burning-Glass I so collect and throw the Rayes on the Paper, that there may be a very great quantity of light pass through it to the Object; yet I so proportion that light, that it may not singe or burn the Paper.

"Instead of which Paper there may be made use of a small piece of Looking-glass plate, one of whose sides is made rough by being rubb'd on a flat Tool with very find sand, this will, if the heat be leisurely cast on it, indure a much greater degree of heat, and consequently very much augment a convenient light.

"By all which means the light of the Sun, or of a Window, may be so cast on an Object, as to make it twice as light as it would otherwise be without it, and that without any inconvenience of glaring, which the immediate light of the Sun is very apt to create in most Objects; ...

"But because the light of the Sun, and also that of a Window, is in a continual variation, ..., I thought of, and often used this, Expedient.

"I procur'd me a small Pedestal, such as is describ'd in the fifth Figure of the first Scheme on the small Pillar AB, of which were two movable Armes CD, which by means of the Screws EF, I could fix in any part of the Pillar; on the undermost of these I plac'd a pretty large Globe of Glass G, fill'd with exceeding clear Brine, stopt, inverted, and fixt in the manner visible in the Figure; out of the side of which Arm proceeded another Arm H, with many joynts; to the end of which was fastned a deep plain Convex glass I, which by means of this Arm could be moved too and fro, and fixt in any posture.

"On the upper Arm was placed a small Lamp K, which could be to mov'd upon the end of the Arm, as to be set in a fit posture to give light through the Ball: By means of this Instrument duly plac'd, as is exprest in the Figure, with the small flame of a Lamp may be cast as great and convenient a light on the Object as it will well indure; and being always constant, and to be had at any time, I found most proper for drawing the representations of those small Objects I had occasion to observe.

"None of all which ways (though much beyond any other hitherto made use of by any I know) do afford a sufficient help, but after a certain degree of magnifying, they leave us again in the lurch. Hence it were very desirable, that some way were thought of for making the Object-glass of such a Figure as would conveniently bear a large Aperture."




Micrographia: or, Some physiological descriptions of minute bodies made by magnifying glasses

This is Robert Hooke's most influential (and beautiful) book, published when he was 30. The cover not only mentions "the Royal Society" twice, it also has the Society's coat of arms and motto: "nullius in verba" - on the word of no one. The popularity of the book helped further the Society's image as the most scientifically progressive organization in the world. For Micrographia, Hooke devised the experiments, often ingeniously given the low-tech means at hand. He developed his own technique for slicing thin sections of a specimen so that he could examine it with his crude illumination system.

In addition, Hooke drew all the images himself: a bee's stinger, a razorblade, snow crystals, wood, cork and insects. The originals are copperplate engravings, some of them fold-outs of an already large (folio) volume. These drawings gave the book much of its power. Two of the drawings from Micrographia reveal Hooke's experimental method.

Observ. IX. Of the Colours observable in Muscovy Glass, and other thin Bodies. (center)

Observ. X. Of Metalline, and other real Colours (right).




Infusoria

Infusoria describes both the medium of decaying vegetable matter in water as well as the microscopic animals that feed on it and form the bottom of the food chain. Van Leeuwenhoek first discovered the "little animals" (kleine diertgens) and animalcules in lake water.

Where did the animals come from? One theory of the time held that they generated spontaneously. To test that theory, van Leeuwenhoek looked for these animals in all kinds of water: rain, sea, canal, well, and river. In it, he steeped everything from ginger to cloves to nutmeg and seemed to have great success with peppercorns.

And then there was vinegar, as he wrote in 1676:

For the last 2 or 3 years, I have not been able to find any little worms, or eels, in the vinegar that I keep in a cask in my cellar, for my household. ... I have diverse times put a little vinegar into a little pepper-water, and have always seen that as soon as the pepper-water was mixed with the vinegar, the animalcules that were in the pepper-water died instantly.

The overlay is the drawing of infusoria accompanying van Leeuwenhoek's letter of December 25, 1702:

And I also saw fixed upon several [duckweed] roots one or even two little cases, of various sizes, whereof the biggest is shown in Fig. 3, RXY. Out of this little case a little animal, with a small part of its body which looked roundish, made its appearance, as in Fig 3., XYZ: and thereupon there suddenly came out of its roundness two little wheels, which displayed a swift rotation, as shown in Fig. 3, a b c. (The draughtsman, seeing the little wheels going round, and always running round in the same direction, could never have enoug of lookin gat them, exclaiming "O that one could ever depist sosonderful a motion!").

We now recognize such creatures as tubicolous rotifers.



Time Line
 
14th century – The art of grinding lenses is developed in Italy and spectacles are made to improve eyesight.
1590 – Dutch lens grinders Hans and Zacharias Janssen make the first microscope by placing two lenses in a tube.
1667 – Robert Hooke studies various object with his microscope and publishes his results in Micrographia. Among his work were a description of cork and its ability to float in water.
1675 – Anton van Leeuwenhoek uses a simple microscope with only one lens to look at blood, insects and many other objects. He was first to describe cells and bacteria, seen through his very small microscopes with, for his time, extremely good lenses.
18th century – Several technical innovations make microscopes better and easier to handle, which leads to microscopy becoming more and more popular among scientists. An important discovery is that lenses combining two types of glass could reduce the chromatic effect, with its disturbing halos resulting from differences in refraction of light.
1830 – Joseph Jackson Lister reduces the problem with spherical aberration by showing that several weak lenses used together at certain distances gave good magnification without blurring the image.
1878 – Ernst Abbe formulates a mathematical theory correlating resolution to the wavelength of light. Abbes formula make calculations of maximum resolution in microscopes possible.
1903 – Richard Zsigmondy develops the ultramicroscope and is able to study objects below the wavelength of light.
The Nobel Prize in Chemistry 1925 »
1932 – Frits Zernike invents the phase-contrast microscope that allows the study of colorless and transparent biological materials.
The Nobel Prize in Physics 1953 »

1938 – Ernst Ruska develops the electron microscope. The ability to use electrons in microscopy greatly improves the resolution and greatly expands the borders of exploration.
The Nobel Prize in Physics 1986 »
1981 – Gerd Binnig and Heinrich Rohrer invent the scanning tunneling microscope that gives three-dimensional images of objects down to the atomic level.
The Nobel Prize in Physics 1986 »

Timeline of the Microscope

14th century: spectacles first made in Italy

1590: Two Dutch spectacle-makers and father-and-son team, Hans and Zacharias Janssen, create the first microscope.

1667: Robert Hooke's famous "Micrographia" is published, which outlines Hooke's various studies using the microscope.

1675: Enter Anton van Leeuwenhoek, who used a microscope with one lens to observe insects and other specimen. Leeuwenhoek was the first to observe bacteria. 18th century: As technology improved, microscopy became more popular among scientists. Part of this was due to the discovery that combining two types of glass reduced the chromatic effect.

1830: Joseph Jackson Lister discovers that using weak lenses together at various distances provided clear magnification.

1878: A mathematical theory linking resolution to light wavelength is invented by Ernst Abbe.

1903: Richard Zsigmondy invents the ultramicroscope, which allows for observation of specimens below the wavelength of light.

1932: Transparent biological materials are studied for the first time using Frits Xernike's invention of the phase-contrast microscope.

1938: Just six years after the invention of the phase contrast microscope comes the electron microscope, developed by Ernst Ruska, who realized that using electrons in microscopy enhanced resolution.

1981: 3-D specimen images possible with the invention of the scanning tunneling microscope by Gerd Binnig and Heinrich Rohrer.

Origin: The origin of the word microscope according to the Online Etymology Dictionary is as follows: 1656, from Mod.L. microscopium, lit. "an instrument for viewing what is small," from Gk. micro- (q.v.) + -skopion. "means of viewing," from skopein "look at." Microscopic "of minute size" is attested from 1760s.

History of the Compound Microscope
Just as the Greeks had a fully functioning radiant heating system operating two thousand years before those only now being introduced in the US, so the origins of the compound light microscope appear to be traced, not to Holland, England or France - but to China which is perhaps appropriate given the present predominance of China in supplying compound light microscopes!

The Water Microscope
According to an ancient Chinese text, the Chinese viewed magnified specimens through a lens at the end of a tube, which tube was filled with varying levels of water according to the degree of magnification they wished to achieve. Ingenious, effective and repeatable in the home, today. That this occurred some 4,000 years ago in the Chow-Foo dynasty and more than 3,500 years before the "father of modern microscopy" was born is quite remarkable.

That these Chinese ancients achieved magnification levels of 150 times today's standard, or 100 moou, is breath-taking. It is as if they developed a town car that achieved Mach II. If they did build such a car, no reference to it has ever been found. Similarly, there is no further known reference to such a compound microscope device until we come back to the Greeks again.