The Science Book

DIRECTORY 333

must exchange some of its pressure

for kinetic energy in order not to

violate the principle of the

conservation of energy. In addition

to mathematics and physics,

Bernoulli studied astronomy,

biology, and oceanography.

See also: Joseph Black 76–77 ■

Henry Cavendish 78–79 ■ Joseph

Priestley 82–83 ■ James Joule 138

■ Ludwig Boltzmann 139

GEORGES-LOUIS LECLERC,

COMTE DE BUFFON

1707–1788

From 1749 to the end of his life,

French aristocrat and naturalist the

Comte de Buffon worked tirelessly

on his monumental work Histoire

Naturelle (Natural History). His

goal was to collate all knowledge

in the fields of natural history and

geology. The encyclopedia spanned

44 volumes when it was finally

completed by his assistants 16

years after his death. Buffon

constructed a geological history of

Earth, suggesting that it was much

older than previously assumed. He

charted the extinction of species

and suggested a common ancestor

of humans and apes, predating

Charles Darwin by a century.

See also: Carl Linnaeus 74–75 ■

James Hutton 96–101 ■ Charles

Darwin 142–49

GILBERT WHITE

1720–1793

British parson Gilbert White was

an unmarried curate who lived a

quiet life in the small Hampshire

village of Selborne. His 1789 book,

The Natural History and Antiquities

of Selborne, was a compilation of

letters written to his friends. In his

letters, White laid out a record

of his systematic observations of

nature and developed his ideas

about the interrelationships

of living things. He was, in

effect, the first ecologist. White

recognized that all living things

have a role to play in what we

would now call the ecosystem,

noting of earthworms that they

“seem to be the great promoters

of vegetation, which would

proceed but lamely without them.”

White’s methods, including taking

recordings in the same places over

many years, were highly influential

on subsequent biologists.

See also: Alexander von Humboldt

130 –35 ■ James Lovelock 315

NICÉPHORE NIEPCE

1765–1833

The oldest surviving photograph

was taken in 1825 by French

inventor Nicéphore Niepce of the

buildings around his country estate

in Saint-Loup-de-Varennes. Niepce

had been experimenting for several

years to find a technique to fix

the image projected onto the back

of a camera obscura. In 1816, he

produced a negative image using

paper coated with silver chloride,

but the image disappeared when

exposed to daylight. Then around

1822, he came up with a process he

called heliography, which used a

plate of glass or metal coated with

bitumen. The bitumen hardened

when it was exposed to light, and

when the plate was washed with

lavender oil, only the hardened

areas remained. It took eight hours

of exposure to fix the images.

Near the end of his life, Niepce

collaborated with Louis Daguerre

on ways to improve the process.

See also: Alhazen 28–29

STEPHEN HALES

1677–1761

English clergyman Stephen Hales
conducted a series of pioneering
experiments on plant physiology.
He measured the water vapor
emitted by the leaves of plants
in a process called transpiration,
and this led him to the discovery
that transpiration drives a
continuous upward flow of
fluid from the roots that carries
dissolved nutrients around the
whole plant. Sap moves from an
area of high pressure in the roots
to areas of lower pressure where
water vapor is transpiring.
Hales published his results
in 1727 in the book Vegetable
Staticks. In addition, he conducted
extensive experiments with
animals, particularly dogs,
measuring blood pressure for the
first time. Hales also invented
the pneumatic trough, an apparatus
used to collect the gases emitted
during chemical reactions.
See also: Joseph Priestley 82–83 ■
Jan Ingenhousz 85

DANIEL BERNOULLI

1700–1782

Daniel Bernoulli was perhaps the
most gifted in a remarkable family
of Swiss mathematicians—his
uncle Jakob and father Johann both
did important work in developing
calculus. In 1738, he published
Hydrodynamica, in which he
examined the properties of fluids.
He formulated Bernoulli’s principle,
that a fluid’s pressure decreases as
its velocity increases. This principle
is key to understanding how the
wings of an airplane produce lift.
He realized that a moving fluid