336
ÉDOUARD BRANLY
1844–1940
A physics professor at the
Paris Catholic Institute, Édouard
Branly was a pioneer in wireless
telegraphy. In 1890, he invented a
radio receiver known as the Branly
coherer. The receiver was a tube
with two electrodes inside it
spaced a little apart, and metal
filings in the space between the
electrodes. When a radio signal
was applied to the receiver, the
resistance of the filings was
reduced, allowing an electric
current to flow between the
electrodes. Branly’s invention
was used in later experiments on
radio communication by Italian
Guglielmo Marconi, and widely
used in telegraphy up to 1910,
when more sensitive detectors
were developed.
See also: Alessandro Volta
90–95 ■ Michael Faraday 121
IVAN PAVLOV
1849–1936
The son of a priest, Russian
Ivan Pavlov abandoned plans to
follow in his father’s footsteps
in order to study chemistry and
physiology at the University of
St. Petersburg. In the 1890s,
Pavlov was studying salivation in
dogs when he noticed that his dogs
would salivate whenever he entered
the room, even if he had no food
with him. Pavlov realized that this
must be a learned behavior, and
started 30 years of experiments
into what he called “conditioned
responses.” In one experiment, he
would ring a bell every time he fed
the dogs. He found that after a
period of learning (conditioning),
the dogs would salivate just when
hearing the bell. In this work,
Pavlov laid the groundwork for
the scientific study of behavior,
although physiologists today
consider his explanations to
be oversimplified.
See also: Konrad Lorenz 249HENRI MOISSAN
1852–1907French chemist Henri Moissan
received the 1906 Nobel Prize in
Chemistry for his work isolating
the element fluorine, which he
produced by electrolysing a solution
of potassium hydrogen difluoride.
When Moissan cooled the solution
to –58°F (–50°C), pure hydrogen
appeared at the negative electrode,
and pure fluorine at the positive
one. Moissan also developed an
electric-arc furnace that could
reach a temperature of 6,300°F
(3,500°C), which he used in his
attempts to synthesize artificial
diamonds. He did not succeed, but
his theory that diamonds could be
made by putting carbon under high
pressure at high temperatures was
subsequently proved correct.
See also: Humphry Davy 114 ■
Leo Baekeland 140–41FRITZ HABER
1868–1934The scientific legacy of German
chemist Fritz Haber is mixed.
On the positive side, Haber
and his colleague Carl Bosch
developed a process for synthesizing
ammonia (NH 3 ) from hydrogen and
atmospheric nitrogen. Ammonia is
an essential ingredient of fertilizers,
and the Haber–Bosch process
allowed the industrial productionof artificial fertilizers, greatly
increasing food production. On the
negative side, Haber developed
chlorine and other deadly gases
for use in trench warfare, and
personally oversaw their use on
battlefields during World War I.
His wife Clara, also a chemist,
killed herself in 1915 in opposition
to her husband’s involvement in
the use of chlorine gas at Ypres.
See also: Friedrich Wöhler 124–25
■ August Kekulé 160–65C. T. R. WILSON
1869–1959Charles Thomson Rees Wilson
was a Scottish meteorologist with
a particular interest in the study
of clouds. To help his studies,
he developed a method of
expanding moist air inside a
closed chamber to produce the
state of supersaturation needed
for cloud formation. Wilson found
that clouds formed in the chamber
much more easily in the presence
of dust particles. In the absence of
dust, clouds only formed when
the saturation of the air passed a
critical high point. Wilson believed
that clouds were forming on ions
(charged molecules) in the air.
To test this theory, he passed
radiation through the chamber
to see whether the resultant ion
formation would cause clouds to
form. He found that the radiation
left a trail of condensed water
vapor in its wake. Wilson’s
cloud chamber proved crucial
for studies in nuclear physics,
and won him the Nobel Prize in
Physics in 1927. In 1932, the
positron was first detected
using a cloud chamber.
See also: Paul Dirac 246–47 ■
Charles Keeling 294–95DIRECTORY