The Scientific Legacy of Antoni Van Leeuwenhoek

196 Chapter 12

Chapter 12 The Scientific Legacy of Antoni Van Leeuwenhoek

This final chapter discusses some of the developments in science on which Antoni van Leeuwenhoek left his mark from his death to the beginning of the 21st century. It will review the influence of his work and listen for the echoes of his name almost three hundred years after his death.

Figure 12.1 Nineteenth-century microscope by George Adams with eyepiece, objective, various attachments and a mirror to illuminate the specimen

Microscopy

Microscopes have become increasingly complex and more versatile, but much easier to use, since the time of Van Leeuwenhoek. Single-lens microscopes went out of use in the 18th century, when compound microscopes with at least two lenses ‒ an eyepiece and an objective ‒ became the norm. Many innovations came from England. Firstly, the illumination of specimens was improved. During Van Leeuwenhoek’s lifetime, John Marshall (1663–1725) had developed a simple illumination system using a mirror attached to the foot of the microscope. John Cuff (1708–1772) used an extra lens, a condenser, in 1744 to concentrate light on the specimen. In 1755, George Adams (1720–1773) developed a microscope with a rotating wheel holding objectives with different powers of magnification. Sliding holders in which a variety of specimens could be mounted at one time can be traced back to the rotating holders on the single-lensed microscopes used by Christiaan Huygens and J. De Pouilly (or Depovilly) in the 1670s, and were developed for use with compound microscopes. The pin on which Van Leeuwenhoek fixed his objects was still a regular attachment provided with the latest microscopes at the end of the 18th century, as were gadgets to allow the observer to watch blood circu- lation in living fish – an obvious development from the aalkijker. The 19th century saw a marked improvement in the quality of lenses. Joseph Jackson Lister (1786–1869) devised a method of correcting image distortion (spherical aberration) and chromatic aberration. By then, microscopes had become so popular that the libraries of the great houses of Western Europe were not considered complete without one, and they were also to be found in the study of many members of the educated middle classes. Books about the use of microscopes such as Henry Baker’s Microscopes made easy also became very popular from the 17th century on. William Henry Fox Talbot (1800–1877) was the first to combine microscopy and photography. In 1834, he also devised a way of improving the contrast in the image of transparent specimens by using polarised light. Six years later, Giovanni Battista Amici improved the image by applying a drop of oil to the specimen and bringing the objective so close that the lens broke the surface of the droplet. Ten years later, he developed these oil immersion lenses for use with water, which improved the power of magnification even further. Microscopy changed dramatically in the 20th century. The Dutch physicist Frits Zernike (1888–1966) received the Nobel Prize in 1953 for his invention of the phase contrast microscope, still in regular use today. This technique, which he developed around 1930, uses a plate beneath the condenser lens that gives different phases to two different light bundles. Interference between the two