Two Leeuwenhoek-type Microscopes

Antoni van Leeuwenhoek made a vast number of microscopes during his lifetime; 248 were sold at auction in 1747, but only 10 are thought to have survived. The microscopes themselves have a single lens and are very difficult to use, as was noted during Leeuwenhoek's lifetime. The Whipple Museum has two 19th-century reproductions by John Mayall.

Frogs and biology classrooms have entwined histories. Though frog dissection became an increasingly common practice in secondary and university education during the 20th century, the practical demands of teaching and the often limited availability of live frogs demanded alternate resources.

Posters and models have the advantages of being reusable, predictable, and large enough for sharing by a large class of students. The Whipple Museum possesses many examples of such teaching tools from the late 19th and early 20th centuries, some of which are explored below:

• Our Deyrolle Model reflects the visual and non-textual focus of secondary school biology in 19th century France, and underscores the mimetic purpose of models as alternatives to live frog specimens.
• Teaching tools from the Cambridge Zoology and Comparative Anatomy Department offer a glimpse into the objects used, and even made, by educators here in Cambridge. They embody the visual sensibilities encouraged by anatomical study.
• Biology instruction today has many more resources than those made of plastic, plaster, and paper. Digital resources, which we will call CyberFrogs, reflect a new, digital approach to scientific training that stands in stark contrast to those represented in our collection.

In the late 18th century, frogs were the talk of the Italian scientific establishment. Two prominent experimentalists, Luigi Galvani and Alessandro Volta, presented novel theories of animal and chemical electricity that they attempted to defend by reference to scientific instruments. At issue was the nature of nervous response and muscular motion in the frog. The Whipple Museum's voltaic piles, Leyden jars, and electro-galvanic machine embody distinct interpretations of the frog's ambiguous body.

In the 1780s, the Bolognese physician Luigi Galvani (1737-1798) conducted a vast range of experiments on electricity's effect on "prepared" frog specimens - that is, frog legs severed at the base of the spine, with nerves exposed. These studies culminated in his Commentary on the electrical force of muscular motion of 1791, which quickly seized the attention of the physical scientist and Galvani's eventual rival, Alessandro Volta (1745-1827).

'Leeuwenhoek' microscopes

The microscope in Image 1 is one of two replica microscopes in the collections of the Whipple Museum, made in imitation of the instruments of the Dutch 'microscopist' Antoni van Leeuwenhoek (1632-1723). The replicas are comprised of two brass plates riveted together, with a single lens held between them. Specimens can be mounted on a needle that is attached to a system of threaded rods, which can be adjusted for coarse and fine focus.

Problems with single-lens microscopes

Leeuwenhoek's microscopes are simple microscopes - they only have one lens. The high curvature of the tiny lens results in a very short focal length; this means that in order to focus clearly the microscope has to be held extremely close to the eye. Leeuwenhoek achieved magnifications of 20X to 275X with the original microscopes, but they were notoriously difficult to use, because of their short focal length and tiny aperture (Image 2). Robert Hooke, the famous microscopist and contemporary of Leeuwenhoek, had the following to say about similar lenses:

"besides, I have found use of them offensive to my eye, and have much strained and weakened the sight, which was the reason why I omitted to make use of them, though in truth they do make the object appear much more clear and distinct, and maginifie, as much as the double Microscope: nay, to those whose eyes can well endure it, 'tis possible with the single Microscope to make discoveries much better than with a double one, because the colours which do much disturb the clear vision in double Microscopes is clearly avoided and prevented in the single." (1)

John Mayall copied these replicas from an original Leeuwenhoek microscope in 1886. Mayall was not attempting to create forgeries to sell ; rather, he was interested in Leeuwenhoek's construction process.

• Read more: John Mayall and his reproductions

Leeuwenhoek's reputation

Leeuwenhoek was given a heroic status through his discoveries made with his microscopes. Many of the observations he made using his simple microscopes were published by the Royal Society of London, to which he was elected a fellow despite not knowing either Latin or English.

To add further to Leeuwenhoek's heroic status, he came from what has been referred to as the 'Dutch Golden Age'. Born in Delft, he was a contemporary of the renowned painter Johannes Vermeer and it has been speculated that it is Leeuwenhoek who appears in the two paintings The Astronomer and The Geographer. However, existing portraits of Leeuwenhoek bear no resemblance to the man in Vermeer's paintings. While Leeuenhoek acted as executor for the Vermeer estate after his death, a biographer of Leeuwenhoek suggests that "Leeuwenhoek may have been a personal friend of the Vermeers".(2)

• Read more: Antoni van Leeuwenhoek

James Hyslop, 'Two Leeuwenhoek-type Microscopes', Explore Whipple Collections, Whipple Museum of the History of Science, University of Cambridge, 2008

Next Article: Mayall's Microscope Reproductions