October 24, 1632 in Delft, Netherlands
August 26, 1723
The Dutch naturalist and microscopist Anton van Leeuwenhoek (1632-1723), using
simple microscopes of his own making, discovered bacteria, protozoa, spermatozoa,
rotifers, Hydra and Volvox, and also parthenogenesis in aphids.
Anton van Leeuwenhoek was born on Oct. 24, 1632, at Delft. His schooling was informal,
probably including some mathematics and physical sciences but no languages. At the
age of 16 he was sent to Amsterdam to become an apprentice at a linen draper's shop
where he remained for about 6 years.
In 1654 van Leeuwenhoek returned to Delft and married Barbara de Mey, who was to
bear him five children. He bought a house and shop and set up in business as a draper.
He remained there for the rest of his life. His wife died in 1666 and in 1671 he
remarried; his second wife bore him one child.
In 1660 van Leeuwenhoek was appointed chamberlain to the sheriffs of Delft, an office
which he held for 39 years. Little is known of his activities for the next 13 years; however,
in his spare time he must have begun to grind lenses to make simple microscopes. As
early as 1668 he took one of his microscopes on a visit to England and used it to
examine chalk from the cliffs in Kent.
In 1673 Regnier de Graaf, a brilliant young physician of Delft, wrote a letter about Van
Leeuwenhoek's work to Henry Oldenburg, Secretary of the Royal Society in London. This
letter was published in PHILOSOPHICAL TRANSACTIONS, and Oldenburg wrote to the author
requesting further communications. Thus began a correspondence with the Royal Society
which was to continue until van Leeuwenhoek's death. All his observations were described
in letters (at least 200), either to the Royal Society or to his friends, that were written in
his own language, Nether-Dutch. He never wrote a scientific paper or a book. His letters
are full of random observations, with little coherence, and were written in a conversational
style. Despite the casual way in which he described his observations, he never confused
the facts with his speculations, and so it is possible to identify easily many of the
organisms he studied from his detailed descriptions.
The Royal Society elected him a fellow in 1680, an honor which pleased him although he
never found time to visit London to sign the register. His discoveries soon made him
famous, and many came to visit him in Delft. His enthusiasm for the study of nature
never waned even in old age, and despite his infirmities he still continued to make
observations and send letters to the Royal Society. After his death on Aug. 26, 1723, his
daughter Maria sent a cabinet to the Royal Society which her father had prepared 22
years previously, containing 26 of his microscopes made from silver.
Van Leeuwenhoek's Microscopes
Apart from those microscopes sent to the Royal Society, van Leeuwenhoek left 247
completely finished microscopes, most of which had an object mounted in front of the
lens, and also 172 lenses mounted between metal plates. Properly speaking, the
instruments were not microscopes at all but simple magnifying glasses. Each consisted of
a single biconvex lens of remarkable clarity which was mounted between two metal
plates. The lens was fixed, and the object to be examined was raised or lowered and
rotated upon its axis by a coarse-threaded-screw. The lenses were of exceptional optical
quality and had magnifying powers ranging from 50 to 200. The short (about 1
millimeter) focal lengths of the lenses would have necessitated placing the eye almost in
contact with the lens, and it is not clear how van Leeuwenhoek obtained the necessary
illumination to achieve his remarkable results. He was always very secretive about his
methods. Clifford Dobell suggested that he might have discovered some simple method
of dark-ground illumination, whereas Barnett Cohen pointed out that the optical
properties of spherical drops of fluid containing the objects under observation may have
been used by van Leeuwenhoek.
Photo: Courtesy of the National Library of Medicine.