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HEAT PENETRATES
EVERY SUBSTANCE
IN THE UNIVERSE
JOSEPH FOURIER (1777–1831)
T
oday, one of the most
fundamental laws of
physics is that energy
is neither created nor destroyed,
but only changes from one form to
another or moves from one place
to another. French mathematician
Joseph Fourier was a pioneer in the
study of heat and how heat moves
from warm places to cool places.
Fourier was interested in both
how heat diffused through solids by
conduction and how things cooled
down by losing heat. His compatriot
Jean-Baptiste Biot had imagined
the spread of heat as “action at a
distance,” in which it spreads by
jumping from warm places to cool.
Biot represented the heat flow in
a solid as a series of slices, which
allowed it to be studied with
conventional equations showing
the heat jumping from one slice
to the next.Temperature gradients
Fourier looked at heat flow in an
entirely different way. He focused
on temperature gradients—
continuous gradations between
warm and cool places. These could
not be quantified with conventional
equations, so he devised new
mathematical techniques.IN CONTEXT
BRANCH
PhysicsBEFORE
1761 Joseph Black discovers
latent heat—the heat taken up
by ice to melt and water to boil
without changing temperature.
He also studies specific heat—
required by substances to
raise their temperature by a
certain amount.1783 Antoine Lavoisier and
Pierre-Simon Laplace measure
latent heat and specific heat.AFTER
1824 By developing the
first theory of heat engines,
which turn heat energy into
mechanical energy, Nicolas
Sadi Carnot provides the
foundations for the theory
of thermodynamics.1834 Émile Clapeyron shows
that energy must always
become more diffuse,
formulating the second law
of thermodynamics.Heat is transferred across
the temperature gradient in
a wavelike movement.Heat penetrates
every substance
in the universe.There is a temperature
gradient between warmer
places and cooler places.Mathematically, a series
of sine and cosine
functions can be used to
represent the movement.