The Science Book

57

See also: Robert Hooke 54 ■ Louis Pasteur 156–59 ■
Martinus Beijerinck 196–97 ■ Lynn Margulis 300–01

SCIENTIFIC REVOLUTION

apparently lifeless substances, that
van Leeuwenhoek discovered the
richness of microscopic life.
Unlike Hooke, van Leeuwenhoek
did not use a two-lens “compound”
microscope, but a single, high-
quality lens—really a magnifying
glass. At the time, it was in fact
easier to produce a clear picture
with such simple microscopics. A
magnification greater than 30 times
was impossible with compound
microscopes since the image
became blurred. Van Leeuwenhoek
ground his own single lens
microscopes, and after years of
honing his technique, managed a
magnification of more than 200
times. His microscopes were
small devices with tiny lenses
just fractions of an inch (a few
millimeters) wide. The sample was
placed on a pin on one side of the
lens, and van Leeuwenhoek held
one eye up close to the other side.

Single-celled life
At first, van Leeuwenhoek found
nothing unusual, but then, in 1674,
he reported seeing tiny creatures

thinner than a human hair in a

sample of lake water. These were

the green algae Spirogyra, an

example of the simple life forms

that are now known as protists.

Van Leeuwenhoek called these

tiny creatures “animalcules.” In

October 1676, he discovered even

smaller single-celled bacteria in

drops of water. In the following

year, he described how his own

semen was swarming with the

little creatures we now call sperm.

Unlike the creatures he had found

in water, the animalcules in semen

were all identical. Each of the many

thousands he looked at had the

same tiny tail and the same tiny

head, and nothing else, and he

could see them swimming like

tadpoles in the semen.

Van Leeuwenhoek reported his

findings in a series of hundreds

of letters to the Royal Society in

London. While he published his

findings, he kept his lens-making

techniques secret. It is probable

that he made his tiny lenses by

fusing thin glass threads, but we

do not know for sure. ■

Antonie van

Leeuwenhoek

The son of a basket maker,

Antonie van Leeuwenhoek

was born in Delft in 1632.

After working in his uncle’s

linen business, he established

his own fabric store at 20 years

old and remained there for the

rest of his long life.

Van Leeuwenhoek’s

business allowed him time to

pursue his hobby—microscopy.

He began in about 1668 after a

visit to London, where he may

have seen a copy of Robert

Hooke’s Micrographia. From

1673 onward, he reported his

findings in letters to the Royal

Society in London, writing

more reports to them than any

scientist in history. The Royal

Society was initially sceptical

of the amateur’s reports, but

Hooke repeated many of his

experiments and confirmed his

discoveries. Van Leeuwenhoek

made over 500 microscopes,

many designed to view

specific objects.

Key works

1673 Letter 1, van

Leeuwenhoek’s first letter to

the Royal Society

1676 Letter 18, revealing his

discovery of bacteria

The world is teeming with microscopic,

single-celled life forms.

Microscopes can be turned on places where there

are no visible life forms.

High-magnification single-lens microscopes reveal

tiny “animalcules” in water and other liquids.