Witnessing the Birth of the Microscope
Looking back to the pioneers’ vision of science
by Brian J Ford
Encyclopædia Britannica: 2000 Yearbook
‘Wonderful’ was the word that marked the dawn of modern biology. Carefully, and with steady hands, the amateur scientist had drawn out a thin tube of glass. He drew up into it a droplet of green slime from the surface of a lake, and fixed it with a drop of wax to the end of the specimen pin on his little microscope. Turning a focussing screw, he brought his home-made lens ever closer to the tiny tube until the image cleared and the contents of the tube fell into focus. His own words describe that moment: ‘I saw so many little animalcules,’ he wrote, ‘and the motion of most of them in the water was so swift, and so various, upwards, downwards and round about, that to see it was wonderful.’ It was August 1674, and microbiology was born.
By the time this astonishing breakthrough was made by Antony van Leeuwenhoek (1632-1723), a middle-aged draper of Delft in the Netherlands, microscopes had already existed for decades. But, whereas his were single-lensed instruments magnifying hundreds of times, the first examples had been compound microscopes, with two lenses. The lens nearest the specimen was a small lens, known as the objective; the image it obtained was viewed with a larger lens next to the eye of the observer, called the eyepiece. The earliest record of a design for a compound microscope dates from 1590 in the Dutch town of Middelburgh, where Zacharias Janssen constructed a hand-held instrument in the form of sliding tubes with a lens at each end. It magnified less than ten times, however, whereas Leeuwenhoek’s single lenses could magnify objects hundreds of times larger than life.
The earliest published picture of an essentially microscopic object I have ever found dates from 1555. It shows various kinds of snow crystals, and one of the images shows a classic example of a six-rayed snowflake. The observer was the Swedish scholar Olaus Magnus (1490-1557). Did he have a microscope of sorts? I doubt it: the structure of a snowflake is visible to the naked eye, and although the picture does show an object normally viewed with microscopes, in my opinion this shows that Olaus was a good observer of small details. The other flakes in his picture include some bizarre inventions - one of them looks like a miniature human hand, for example.
Ornately-designed compound microscopes became popular possessions of wealthy investigators in the middle seventeenth century. Some of the finest were made in London and were constructed of card and wood with a covering of polished fish-skin. It was with one of these fine microscopes, made by Christopher Cock in London, that the Royal Society’s demonstrator Robert Hooke (1635-1703) first saw living cells on March 25, 1663. He drew them in a specimen of living moss. On April 13 that year he studied the same structures in a fine section cut from a cork, and named these tiny box-like chambers ‘cells’ - the name they have had ever since. Hooke’s observations were brought out in a magnificent folio book called Micrographia in 1665. It became a best-seller, and was very influential. Samuel Pepys (who had bought a microscope when he was at the Navy Office) wrote in his diary that he sat up half the night reading his newly-purchased copy of Hooke’s book.
The compound microscope has since become the most familiar of all items of scientific apparatus, and is an icon that is regularly used to advertise science. Few people, however, have looked at life through a microscope - and even fewer have any understanding of the extraordinary story of this fascinating instrument. The benefit of using a conventional compound microscope was convenience. The instrument stood upon the philosopher’s table, and the eyepiece was comfortably situated for lengthy studies. Although many-lensed compound microscopes are more familiar, it was the single-lensed simple microscope, as it is called, which gave us the major discoveries on which the modern era of the biosciences is founded. In this chapter we recreate some of the experiments made with these little-known instruments. It is time to celebrate their importance to modern science.
In the year following the publication of the first edition of Micrographia, Antony van Leeuwenhoek paid his only visit to England, sailing up the Thames River to London. During this trading visit he was doubtless shown a copy of Micrographia. It contains some vivid engravings of textiles, looking as vivid as modern scanning electron micrographs. The first published description of a simple microscope also appears, tucked away in a rarely-quoted passage in the Preface to Micrographia. Hooke’s suggested design, where you grind a tiny plano-convex lens and fix it in a hole in a sliver of metal, is exactly how Leeuwenhoek made his. The first specimens Leeuwenhoek studied (cork, elder pith and the quill of a feather) are identical to specimens described in Hooke’s book, and even in the same order. Leeuwenhoek’s visit was in 1666; his first recorded microscopes date from 1673. Simple microscopes were much smaller than the compound type. The microscope we now know as Leeuwenhoek’s type was hand-held, and using it for lengthy observations was tiring. Hooke acknowledged that you obtained far clearer images with a simple microscope, but said he rarely employed them in his own work because they were so troublesome to adjust and tiring to use.
To this day, people persist in dismissing simple microscopes as providing poor quality images, and even the most recent books reiterate the view that little fine detail could be seen with them. These microscopes are widely misunderstood. Their history is misrepresented, the achievements of the pioneers too often dismissed as exaggeration or good luck, and few people have any real idea of what those ground-breaking scientists could truly see. It is time to replace that negative view with a far more positive proposition. In fact, compound microscopes tended to magnify aberrations as much as images. The simple microscope produces an image of startling clarity. Most text-books will tell you that the image from a simple microscope is fringed with rainbow-colored hues and its detail is indistinct. The single fact that unites the authors of those accounts is that they have never tried to use a simple microscope. In this way a myth is perpetuated from one generation of textbooks to the next.
The idea that images produced by single lenses are rainbow-hued stems from the phenomenon of chromatic aberration. This effect is due to the fact that longer wavelengths of light, towards the red end of the spectrum, are refracted less than light nearer to blue. In practice, this is less of a problem with single lenses than one might anticipate. As the photographs show, although there is some slight spurious coloration in the images obtained with high-power simple microscopes, they do not detract from the essential clarity of the image. When used properly, the microscopes can provide excellent images.
What of the specimens prepared by these great pioneers? Modern writers have perpetrated misapprehensions here, too. Says one book on the preparation of microscope specimens: ‘No preparations from the seventeenth century have survived, for it is almost certain that all were only of a temporary kind. The detail visible in the usual dry mounts is minimal, and they are prepared with little finesse.’ In each detail this popular view is incorrect. I found that the first specimens prepared by Leeuwenhoek had survived, after all; with the kind encouragement of Sir Andrew Huxley, President of the Royal Society, I was given full access to Leeuwenhoek’s papers and found nine specimen packets. The specimens themselves included samples of algae, slices of optic nerve, and hand-cut sections of plant material. The best were of exceptional quality - indeed Leeuwenhoek’s sections of cork and elder pith are better than those in some recent publications. They had lain untouched for over three centuries when I discovered them.
Many institutes have given me full access to their collections of instruments, ranging from the Royal Zoological Society in Antwerp and the Jodrell Laboratory at Kew Gardens in London, to the Deutsches Museum in Munich and the Museum for the History of Science at the University of Utrecht; the Museum for the History of Science in Oxford and the Billings Collection at the National Institutes of Health in Bethesda, Maryland. In other cases I have been given replica microscopes made by enthusiasts including Dennis Belford of Lothian, Scotland; Henri Hansen of Antwerp, Belgium; and the late Horace Dall of Luton, England. To all these sources, and so many others, I am grateful.
To commemorate the dawn of a new millennium, these historic pictures allow us to retrace the steps of some of the great pioneers and see what they saw. Using those original instruments, and supplementing the research with some modern lenses that are similar to the old designs, I have recreated some of the crucial observations made by the first investigators of the modern era of biology. They reveal extraordinary detail, and show that the most primitive of instruments can provide results that compare with the microscopes in use in today’s laboratories. Leeuwenhoek’s tiny microscopes could clearly reveal living bacteria, for example. In one stunning picture, obtained with a surviving Leeuwenhoek microscope at the University of Utrecht, Netherlands, I captured an image of a thin film of my own blood. The fact that you could perceive blood cells is itself surprizing to many scientists (a recent experimenter tried to observe blood cells with this same instrument but could make out nothing but blurred patches). Far more exciting was the revelation that the field of view captured a white blood cell, a polymorphonuclear granuloctye, which is characterised by having a lobed nucleus. The Leeuwenhoek lens had even resolved these tiny structures, each about two thousandths of a millimeter in size. That’s smaller than many bacteria.
One of the most popular forms of simple microscope was known as the screw-barrel, for it featured a hand-held cylindrical viewer that was held up to the light. The specimens were loaded into perforated bone or ivory sliders, held between disks of glass-like mica, and a spring-loaded aperture allowed the user to slide them into the microscope. These were easy to use and robust in construction. However, one fashionable specimen was not suitable for observation in this way. I refer to Hydra, the fresh-water polyp, which had been popularised by the work of Abraham Trembley (1710-84). At the age of thirty this Swiss philosopher he had been appointed tutor to the two young children of Count Bentinck of The Hague in the Netherlands, and he turned to Hydra as an object for study. He published pioneering experiments in grafting and regeneration, and Hydra (first described by Leeuwenhoek on Christmas Day 1702) soon became a popular object for microscopical study. The organism needs space in which to expand, and these observations necessitated a new kind of microscope. The result was the design promulgated by John Cuff, in which a watch-glass can be rested on a circular stage and the lens brought into focus on a transverse arm set above it. This is the kind of microscope owned by Carl Linnaeus (1707-1778), which I have been privileged to use in Uppsala, Sweden.
By the early nineteenth century an advanced version of this design was being used by a young Scottish surgeon to study plant tissues. Robert Brown (1773-1858), who had travelled to Australia in search of undiscovered plants, was fascinated by the reproductive mechanisms of plants and spent much time studying orchids. As he sat observing tissue structure, a common feature of the living cells suddenly attracted his attention. ‘In each cell of the epidermis ... a single circular areola, generally more opaque than the membrane of the cell, is observable.’ Stimulated by his discovery, he looked again at specimens from other plant families. He soon found that this new structure was ‘not confined to the Orchideae but is equally manifest in many other Monocotyledenous families; and I have even found it ... in the epidermis of Dicotyledenous plants.’ He had recognised one of the most fundamental features of living cells. He did not care for the term areola, however, and soon coined the term we know today, redefining it as ‘this areola, or nucleus of the cell as perhaps it might termed.’ It was 1828.
Brown was not the first person to observe the nucleus of living cells. Leeuwenhoek had recorded nuclei, most notably in the blood cells of fish, but had not recognised their widespread occurrence elsewhere in nature. Leeuwenhoek also observed the ceaseless motion of tiny particles, resulting from the bombardment of particulate matter by moving molecules in a surrounding fluid. In the summer of 1827 Robert Brown made a systematic study of this phenomenon, and showed that it occurred in dead matter as well as living cells. The subject was exhaustively investigated by Albert Einstein in 1905, and we now know this phenomenon as Brownian Movement.
Because both Leeuwenhoek and Brown used simple microscopes with a single, tiny lens, doubt has been poured upon their veracity. Leeuwenhoek has been dismissed as a dilettante, who had a fertile imagination. Brown’s abilities to observe the motion which now bears his name has often been misrepresented; most text-books say he claimed to have observed the movement ‘of pollen grains’. That is untrue. The tiny particles he studied were found within the pollen-grains. Many of them are smaller than bacteria. Some major journals have recently concluded that Robert Brown could never have witnessed the phenomenon that bears his name with such an unsophisticated microscope, but I have repeated his experiments with his original microscope preserved at the Linnean Society of London, and can confirm that the phenomenon can be vividly revealed. Similarly, when modern-day studies have been made of a Leeuwenhoek microscope, it has often proved impossible to make out fine detail. An expert assessment of one of Robert Brown’s microscopes said it might have been useful as an aid for dissection, but could not have revolved structures as small as a nucleus. These accounts result from improper use of the instrument, for when it is set up it provides images of considerable clarity.
Here we see a selection of micrographs, many of them never before published. They are presented to reveal what the pioneers could see, for all forms of image enhancement have been eschewed. The lesson we can learn is salutary: our modern era of science, based on an understanding of microscopic structure, did not result solely from the use of achromatic microscopes. The key discoveries were made with simple microscopes. Indeed, many of the crucial discoveries could have been made using nothing more than a Leeuwenhoek microscope from the 1600’s.
These simple microscopes were made of brass and are beautifully finished. One of the most successful manufacturers was the London firm of Bancks & Son. They are hardly known to historians of science, being listed in a few catalogues of manufacturers but not otherwise documented. They clearly must have been influential in their time. Robert Brown utilized their instruments in his research, and so did Charles Darwin. The firm even supplied the Prince of Wales, later King George IV. The lack of interest in their products is a symptom of the disinterest shown in simple microscopes as instruments for serious research. Yet they were immensely popular in their time. The most fantastic microscope ever made was created in 1761 by George Adams for King George III. It does have a compound microscope tube as an accessory, though it is primarily designed as a simple microscope. With its grotesque solid silver construction and Gothic embellishments, it is an unforgettable work of art, as much as an instrument of science.
Perhaps the most advanced simple microscope of all is a pocket microscope made by the London firm of Dollond in the 1830’s. It is rich in design features associated with modern microscopes. The mechanical stage can rotate, and the position of the specimen is controlled by two milled controls that allow the observer to rack across the specimen from left to right, or to move it up and down in the field of view. There is a concentric fine focussing control, near the base of the body tube. This microscope was equipped with a range of interchangeable lenses, each mounted on a brass slider, the highest magnification being 480x. [NOTE: This is pronounced ‘480 times’, and not, as one sometimes hears, ‘480 ecks’.] This lens is now missing, though other similar lenses were reckoned to offer a magnification up to 800x.
Simple microscopes remained popular for longer than an historian of science might anticipate. By 1830 achromatic compound microscopes were becoming available, in which convex and concave lenses were combined to cancel out the annoying tendency of spurious colors to appear in objects under high magnifications. Today’s optical microscopes are directly descended from the Victorian achromatic instruments. In 1848 Charles Darwin was still advising the use of a simple microscope, and Fields’ Simple Microscope won a major design award in London as late as 1862.
The essential design of these microscopes is with us today. The seventeenth-century compound microscope, with its sliding focus, its table-level stage and its pillar for support, eventually died out. When achromatic compound microscope tubes began to appear it was on the Bancks type of simple microscope stand that they were installed. This design features a main column supporting fine focussing controls and the stage on which specimens are placed; a transverse arm bearing the optical components; a substage illuminator and a condenser to direct light through the specimen itself. The more advanced microscopes (like the Dollond design) even featured a mechanical stage. Modern microscopes are an elaboration of this early design, and remind us that the pioneering work of the designers of simple microscopes lives on, in a more evolved reincarnation, in the laboratories of a new millennium.
Brian J Ford CBiol FIBiol FLS is a research biologist and an authority on the microscope. He is the author of many best-selling popular science books, published in over 90 editions around the world. A resident of Cambridgeshire, England, he is a Fellow of Cardiff University and serves on the governing bodies of several academic institutes in Britain and the United States.