The first simple insect viewers.
The first simple insect viewers.
Before the 1830s there were two types of microscope, the simple and the compound.
A Simple Microscope has a single lens. This was usually of small aperture to reduce the blurring or 'spherical aberration' caused by the curvature of the lens. Simple microscopes relied on natural light around the object or a direct form of illumination passing right through it if it was translucent. As many kinds of lens can be used in the hand as a 'simple' microscope, it is not really possible to assign a starting date for the science. The diagram to the left shows a suggested design by Descartes for a hand-held simple microscope using a concave mirror to produce a virtual image when held close to the eye in 1637. The first known image of a microscope is a drawing by Isaac Beeckman of six years earlier. Quite apart from the quality of its workmanship, the user required good eyesight to make the most of such an instrument.
The 'inventor' of the microscope is probably lost to history, however microscopy as we understand it was possibly introduced by the Dutch spectacle-makers Zacharias and Hans Janssen of Middelburg. The Janssens produced a compound microscope in 1595 capable of magnifying specimens up to ten times when fully extended.
A Compound Microscope has a convex objective lens (closest to the object being viewed e.g. a specimen) and convex eyepiece. The ocular lens magnifies the 'real' image that has already been formed by the objective such that the observer is actually viewing an enlarged virtual image. The development of the compound microscope is closely tied in with that of another instrument, the telescope but for a skilled user the simple microscope yielded better results until the mid 18th century. Kircher described various 'smicroscopes' (sic) in 1646, concluding that the best type was a tube containing a glass sphere at one end onto which you would place the object to be viewed. i.e. the best simple microscopes were still being recommended above the compound types available.
Early compound microscopes were very inefficient and the image quality was affected by significant chromatic and spherical aberration, but quite large instruments (over a foot long) with a reasonably high power were available by the first decade of the seventeenth century.
Early definitions and writings on the microscope
In 1625 Stelluti published his Anatomy of the Bee, as Revealed by the Microscope. The Italians were at the forefront of microscope development in this period. Although the word 'microscope' does not occur in English before 1656 the Italians at the Accademia dei Lincei referred to a 'microscopium' in 1625. Robert Hooke, Secretary of the Royal Society in London, published his Micrographia forty years later containing some remarkable illustrations of the enlarged items that he had observed, including the famous engraving of a flea.
Peter Borel's Classification (1655) from the De Vero Telescopii Inventore
A microscope, whether it be a flea glass or a fly glass, whereby a flea is enlarged the size of a camel, and a fly to the size of an elephant, is made out of two glasses inclosed in a small tube: the glass nearest the eye is convex and made out of a small segment of a spherule, whose diameter should be two inches: the other glass is plane.
A microscope can also be made of two convexes, and is superior.
Some are made of a single spherule inclosed in a tube, opposite the end of which either a small glass box is arranged for the reception of sundry tiny objects, or a saucer is applied for the examination of liquids.
Or the model of the tube may be a system of pipes, which can be shortened and lengthened at pleasure, and under which objects may be applied: also, more glasses, even three or four, can be mounted, and so objects appear enlarged.
The name "Microscope" which some claim was invented by Giovanni Faber was only in common use from the 1650s.
Leeuwenhoek's simple microscope
From some point before 1673 the Dutch draper and surveyor Antoni van Leeuwenhoek (1633-1723) used melted glass balls to form lenses for apparently crude simple microscopes that nevertheless magnified up to 275 times! Modern tests have concluded that he could have achieved a resolution of two micrometres. A surprising number were produced, perhaps over 400, because it was impossible to achieve a standard magnification. For that reason each microscope was produced for a specific specimen and it is believed that they were supplied with the specimen fixed in place. Leeuwenhoek's work has added significance because he also published his observations in the Philosophical Transactions of the Royal Society. These notes and illustrations from 1693 tell us, for example, that one of the first things he observed with his microscope was a scab from his own nose.
Leeuwenhoek's Simple Microscope is shown in the above picture gallery viewed from both the front and rear. The specimen was attached to the spike which could be positioned in front of the tiny double convex lens by means of a screw-thread. Sadly the BOA Museum does not have an actual example, though it does display a modern replica (devoid of any specimen), four views of which feature in the picture gallery. It was made for us by Museum Boerhaave in Leiden. Replicas of Leeuwenhoek's Simple Microscope have been produced since the late 19th century. The chances of acquiring a real historical example are, however, remote. Conflicting reports suggest that there are between seven and twelve genuine examples in the world.
Entomologists continued to use microscopes based on a similar principle for many years. To the left is an ivory flea or 'acorn' microscope, though you might not at first recognise that it is a microscope. The handle is shaped for ease of holding whilst the lens, beneath the acorn-shaped lid, is kept very close to the observer's eye. The body of the case could also be used as a 'live' box for storing specimens. This type of microscope persisted from the early 1700s to the later 1800s and the vast majority are unsigned. Ours is possibly English.
Another popular type of instrument represented in our collection is the Wilson Screw-barrel type of microscope. This microscope is certainly small (the image shows it against a five centimetre scale) but it is not so simple. It has several component parts and indeed some of ours are missing. Present are the ivory handle and open cylindrical 'screw-barrel' head containing a metal spring, plates and stained ivory aperture but missing is the adjustable screw that allowed it to focus. Included are four ivory mounted objectives (numbered 1 to 4) and a metal slide rack, though unfortunately all its apertures are now empty. The condenser mount is also missing. One of the plates in the barrel is slightly curved to accommodate a glass cylinder for instance to facilitate the observation of pond life.
The instrument is a tight fit. Cases such as this have a tendency to shrink with age. The cylindrical shape of this particular case, however, is unusual. It is covered in shagreen and has a green velvet lining. The portable screwbarrel type of microscope was invented by James Wilson in 1702 though the idea had been pre-empted by Nicholas Hartsoeker in 1694. Two of the most common makers were Culpeper and Scarlett. The early models like this one were of ivory, but later on brass was the preferred material.
Further study: For more information on this type of microscope see:
A.V. Simcock 'Edmund Culpeper and the Screwbarrel Microscope', Bulletin of the Scientific Instrument Society No 88 (2006), pp.2-9
Competitive manufacture of microscopes in London and elsewhere
Monocular and tripod microscopes could be purchased from the great rival London opticians of John Yarwell (d.1712) or John Marshall (c.1659-1725). Our illustration is of a 'Double Microscope' on Yarwell's trade card from 1697. Apprenticed in 1662, John Yarwell became a Freeman of the Spectacle Makers' Company in 1669 and served as Master Spectacle Maker in 1684. He removed to the Sign of Archimedes and Crown in 1698.
John Marshall was very influential in developing the side-pillar as introduced by Robert Hooke. Marshall added stage plates and fish plates to this pillar which could be inclined to transmit light straight through an object, for instance a frog by which the user could test for himself William Harvey's theory of the circulation of the blood (1628). Microscopes were now good enough to see the capillaries that Harvey (1578-1657) had predicted.
Marshall's 'Double' microscope and the Culpeper type of tripod design (from about 1730) were especially popular, particularly after the basic designs were modified by Cuff.
The Culpeper-type includes a tripod stage with a mirror beneath for reflecting light from below. Visually they were not unlike Campani's instruments of forty or more years previously. In some senses this was a retrograde step as the instrument could not be inclined and was thus uncomfortable to use, the owner having to peer into it directly from above.
The example we illustrate here has no maker's name attached but we can admire its scroll-shaped legs. It also features a screw-on eyepiece, rack and pinion focusing movement with milled edge control wheel and a sprung stage above a square wooden base with accessory drawer. This drawer, lined with green baize, contains four replacement objectives plus other accessories including a librachrome fitting, a round mounted bulls-eye condenser lens on a brass rod, a fish plate with green silk ties, a spike with tweezers, a glass observation rod with cork and five bone-mounted slides. It is probably English. English microscopes were some of the finest in the world. In 1739 the great Professor Samuel Klingenstierna of the University of Uppsala, Sweden bought a Culpeper-type microscope made by Matthew Loft.
As mentioned, Josephi (Giuseppe) Campani in Italy was another famous maker. A print in the College collection shows Iosephi Campani's Novum Microscopium being used in an anatomical investigation (1686). You may click on the image of this print to enlarge it.
The artist has also included a super-sized version of the microscope on the table to the left so that the detail of its construction might be seen. In this case the user is not studying a translucent slide but directly examining an opaque surface - a wound or incision. The light by which this examination could be performed might be reflected from a candle or simply taken from the sky.
In one of his eighteenth century trade cards George Adams, at Tycho Brahe's Head in Fleet Street, advertised microscopes 'as to discover the Circulation of the Blood in Animals, the Peristaltic Motion of Insects, the Farinae of Vegetables, and many other surprising Phaenomena, otherwise not perceptible'. Both the Adams father and son and also Benjamin Martin introduced many modifications to the side pillar and many new accessories.
Despite all these extras microscopes generally grew lighter in weight which made them more convenient to use. At the end of the eighteenth century Harmanus van Deijl (1738-1809) successfully applied the concept of Dollond's achromatic telescope lens to the small lenses of compound microscopes. This tackled the annoying coloured edges seen by observers but spherical aberration remained a problem with glass microscope lenses until Joseph Jackson Lister's discoveries in 1830.
It has to be said, however, that until the nineteenth century most microscopes were sold as gentleman’s toys rather than instruments for serious scientific experimentation. They were provided with expensive cases, lined with plush velvet and compartmentalised to accommodate various accessories that often went unused. To avoid disappointment the makers often supplied the purchaser with a set of pre-prepared slides.