The Science Book

334

ANDRÉ-MARIE AMPÈRE

1775–1836

Upon hearing of Hans Christian
Ørsted’s accidental discovery
of the link between electricity
and magnetism in 1820, French
physicist André-Marie Ampère
started formulating a mathematical
and physical theory that explained
their relationship. In the process,
he formulated Ampère’s law, which
states the mathematical relation
of a magnetic field to the electric
current that produces it. Ampère
published his results in 1827,
and his book, Memoir on the
Mathematical Theory of
Electrodynamic Phenomena,
uniquely deduced from experience,
gave a name to this new scientific
field—electrodynamics. The
standard unit of electric current,
the ampere (or amp), is named
after him.
See also: Hans Christian Ørsted
120 ■ Michael Faraday 121

LOUIS DAGUERRE

1787–1851

The first practical photographic
process was invented by the
French painter and physicist Louis
Daguerre. From 1826, Daguerre
collaborated with Nicéphore Niepce
on his heliographic process, but
this needed at least eight hours of
exposure. Following Niepce’s death
in 1833, Daguerre developed a
process in which an image on an
iodized silver plate was developed
by exposure to mercury fumes and
fixed using saline. This reduced
the exposure time required to
20 minutes, making it practical to
take photographs of people for the
first time. Daguerre wrote a full

description of his process, called

the daguerreotype, in 1839, and

it made him a fortune.

See also: Alhazen 28–29

AUGUSTIN FRESNEL

1788–1827

French engineer and physicist

Augustin Fresnel is best known

as the inventor of the Fresnel

lens, which allows the light from

a lighthouse to be seen over

greater distances. He studied

the behavior of light, building

on the double-slit experiments of

Thomas Young, with whom he

corresponded. Fresnel conducted

a great deal of important theoretical

work on optics, producing a set

of equations describing how light

is refracted or reflected as it

passes from one medium to

another. The importance of

much of his work was only

recognized after his death.

See also: Alhazen 28–29 ■

Christiaan Huygens 50–51 ■

T homa s You ng 110 –11

CHARLES BABBAGE

1791–1871

British mathematician Charles

Babbage conceived the first digital

computer. Appalled by the number

of errors in printed mathematical

tables, Babbage designed a

machine to calculate the tables

automatically, and in 1823 hired

engineer Joseph Clement to build

it. His “Difference Engine” was to

be an elegant contraption of brass

cogwheels, but Babbage got only

as far as a prototype before running

out of money and energy. In 1991,

scientists at London’s Science

Museum built a Difference Engine

to Babbage’s specification, using

only technology that would have

been available at the time, and it

worked, though it tended to jam

after a minute or two. Babbage

also dreamed of a steam-powered

“Analytical Engine,” which would

take instructions on punched

cards, hold data in a “store,” carry

out calculations in the “mill,” and

print out the results. This might

have been a real computer in the

modern sense. His protégée Ada

Lovelace (the daughter of poet Lord

Byron) wrote programs for it, and

has been called the world’s first

computer programmer. However,

the Analytical Engine project

never got off the ground.

See also: Alan Turing 252–53

SADI CARNOT

1796–1832

Nicolas-Léonard-Sadi Carnot was

an officer in the French army who

semiretired on half-pay to Paris in

1819 to devote himself to science.

Hoping to see France catch up with

Britain in the Industrial Revolution,

Carnot began designing and

building steam engines. His

research led to his only publication,

in 1824, Reflections on the Motive

Power of Fire, in which he noted

that the efficiency of a steam

engine depends principally on the

temperature difference between

the hottest and coldest parts of the

engine. This pioneering work

on thermodynamics was later

developed by Rudolf Clausius in

Germany and William Thomson,

Lord Kelvin in Britain, but was

largely ignored in Carnot’s lifetime.

He died in relative obscurity during

a cholera epidemic, at just 36.

See also: Joseph Fourier 122 ■

James Joule 138

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