The Problems with Lenses, and the 19th-century Solution

One of the central themes of the history of the microscope is the history of lens development. Until 1830 two problems hindered lens manufacture: spherical aberration and chromatic aberration. Around 1830, in collaboration with Joseph Jackson Lister, William Tulley made one of the first microscopes that corrected for both chromatic and spherical aberration.

Scientific instruments are not only things that we can tinker with. 'Paper tools' like books and journals are important examples of scientific instruments, though they attain that status in unfamiliar ways. How these texts were created and organised into libraries could have great consequences, and could even transform the way that their contents were perceived, interpreted, and made scientifically meaningful.

In 1882, W.T. Sedgwick published an extensive review article in a new Cambridge periodical entitled "Studies from the Biological Laboratory." In it, he described the use of frogs as objects for testing the nature and origin of reflex motion. After 'decerebrating' frogs - that is, removing their brains through vivisection - frogs would be immersed in water of varying temperatures and their responses observed. Such interest in reflexes followed closely on Galvani and Volta's experiments on stimulation. Sedgwick made careful use of work from his own Cambridge laboratory, and especially that of its founding professor, Michael Foster. He cited dozens of articles from journals printed throughout Europe and America.

The Whipple Library holds the books that served Foster's young department and supplied Sedgwick's citations. These books represent the peculiar ways that researchers here in our own university discovered general scientific meaning in the study of frogs' bodies. The Foster Collection comprises thousands of articles from scientific journals, chapters from books, dissertations, and other texts that have been removed from their original binding, rearranged, and rebound in hardback editions according to Foster's own taxonomy. It includes 5,221 pamphlets that fill around 200 volumes and cover all aspects of 19th century physiology. Rather than sorting articles according to their original journal or book of publication, Foster created a library that placed each article alongside other articles that consider the same part of the body. Physiological studies of the nervous system - whether that be human, cat, or frog nerves - are all conjoined. Investigations into the digestive system, for example, are all collected in a volume labeled "Digestion."

Printed works like these may not seem to be scientific instruments in a conventional sense. Through the content and organisation of its papers, however, the Foster Collection manifests distinctly modern ways of using frogs to produce general scientific knowledge. These books exemplify how animal diversity was useful to scientific work at a certain moment in time, but also how it could also be ignored or denied. Where zoology and some other biological sources aim to classify and distinguish animals, this library exemplifies physiologists' opposite impulse: to homogenise or assimilate the processes that make them alive.

Read more: an overview of the Foster Collection from the Whipple Library

This page explores the history of the Cambridge Department of Physiology, focussing on two reccurring themes: frequent collaborations with instrument manufacturers, and a reliance on "the physiologist's little friend the frog," as A.V. Hill once described it, as a research specimen. The foundation of the Department created a demand for physiological instruments and thus a demand for a local instrument company. The Cambridge Scientific Instrument Company, created in 1881, addressed this need.

Early Cambridge Physiology and the Cambridge Scientific Instrument Company

In the 19th century, the University of Cambridge was notorious for its conservatism toward science. It finally responded to calls for change by founding three scientific institutions in the 1870s: the Cavendish Laboratory, the Department of Mechanism and Applied Mechanics, and the Physiological Laboratory. This created a large, pressing demand for a variety of scientific instruments, but the departments' in-house instrument makers were unable to completely satisfy their needs. The crisis was resolved in 1881 with the foundation of the Cambridge Scientific Instrument Company (CSIC).

In its early years, most of the Company's business was generated by the Department of Physiology. Sir Michael Foster (the founder of the Department and the compiler of our Foster Collection) and his students sometimes collaborated with CSIC to create and improve instruments for their experiments on frogs. For instance, the Company commercially produced two frog cardiographs, each designed by one of Foster's former students. One of these men, Walter Holbrook Gaskell, used his frog cardiograph to make crucial discoveries, including the path of electrical conduction through the heart.

Cambridge physiologists continued to collaborate with CSIC for the entirety of its existence, but the scientist with the closest links to the Company was Keith Lucas (1879-1916). Lucas served both as a Trinity College lecturer in Natural Sciences and as a CSIC board member. He was an extremely skilled instrument designer, and the Company commercially produced several devices that he had originally custom-made for his own experiments on frogs. One of these is the Lucas Pendulum, which could open successive electrical circuits for short periods of time, thus stimulating a nerve or muscle. The Whipple Museum holds two CSIC Lucas Pendulums: Wh.5000 (1907) and Wh.4133 (1938). The production date of Wh. 4133 reveals that Lucas' pendulum was so excellent that it was sold for over thirty years with only minimal changes to its design.

Though Lucas' instruments could be used with multiple species, he described frog vivisections in all twenty-three articles that he published in the Journal of Physiology. In his only paper that was not dedicated to frog research, Lucas still used frog muscle, because he was so familiar with it, to calibrate his apparatus before beginning his actual experiments on crayfish.

Two types of aberration

Spherical aberration results in a partially blurred image, and is caused by light passing through different areas of the lens. This results in different parts of the image focusing at a different distance between the lens and the eye of the observer. If this is left uncorrected, there is no way to focus the whole of the image at the same time. Towards the end of the 18th century this problem was solved by using a certain combination of lenses, one correcting the aberration of the other.

A similar solution was found, in 1830, for chromatic aberration. This problem results from the fact that the wavelengths of different colours refract to differing degrees, so blue will focus closer to the lens than red The consequence of this is a halo of colours around any object you look at. For example, in Image 1, slight chromatic aberration can be seen around the head of the flea (top right). In this case the aberration is not sufficient to obscure the image, and the flea is clearly visible in other areas, for example its legs (bottom left).

A 'corrected' microscope

The description of the first lenses that were free from both of these aberrations was published in 1830 by Joseph Jackson Lister (1786-1869). Although achromatically corrected lenses had been made before Lister's work, he was the first to describe a full achromatically and spherically corrected optical system for the compound microscope. Lister was not an instrument maker, so he worked with craftsmen such as William Tulley to produce the lenses (Image 2). In the first decades of the 19th century, many attempts had been made to make achromatically corrected lenses for the microscope. Tulley himself had attempted and failed to make a lens that was corrected for both aberrations in 1807.

It was easier to deal with abberation for telescopers lenses, and as solutions were already known before the time microscope lenses were corrected. Telescope lenses are larger, and so it is far easier to grind them for correction. Alternatively mirrors could be used, and reflecting telescopes were popular. Reflecting microscopes were made, but like the lenses, small mirrors were difficult to construct accurately.

Whilst the removal of chromatic and spherical aberration was certainly an important step forward in the development of the microscope, it is not clear how directly it affected the history of scientific discovery.