molecules in the object move faster.
When this happens, the temperature of
the object rises.
Heat travels in three ways: by conduction,
by convection, and by radiation.
Conduction is the flow of heat inside an
object. It is also the flow of heat between
objects in contact with each other. An
example is the flow of heat from a hot
frying pan to food placed on the pan to
cook.
Convection is the flow of heat caused by
the motion of a liquid or a gas. An
example is the heating of water in a teakettle.
As water is heated, the molecules
that make up the water rise and the heat
spreads.
Heat radiation is the flow of heat
between objects that are not in contact
with each other. An example is the heat
felt by someone standing a distance
away from a hot stove.
Radiation from the sun gives Earth most
of its heat. Energy from the sun’s radiation
is stored in such fuels as coal, oil,
gas, and wood. These fuels can be
burned to provide more heat.
#More to explore
The heat of a fire cooks peppers on a grill. Energy • Molecule • Sun
32 Heat BRITANNICA STUDENT ENCYCLOPEDIA
Heather
Scotland is famous for its rolling hills
covered with the beautiful purple flowers
of the plant called heather. Scotland
is not the only place that heather grows,
however. Heather grows throughout
Great Britain, northwestern Europe,
northern Asia, and North America.
Heather grows well in poor soil. It needs
lots of sunlight to grow.
Heather is an evergreen plant. This
means that it does not lose its leaves in
autumn. Heather usually does not grow
taller than 3 feet (0.9 meter). Its leaves
are most often green. But they also may
be gray, yellow, gold, orange, or red.
Heather has tiny, bell-shaped flowers
that are pink, rose, purple, red, or white.
Heather is a useful plant. It can be made
into brooms and baskets. Long ago, the
people of Scotland made houses of
heather mixed with mud and straw.
Heather also attracts bees and butterflies.
The scientific name of heather is Calluna
vulgaris. Heather belongs to a family,
or group, of plants called heaths.
Other plants in the heath family include
the blueberry plant.
#More to explore
Plant • Scotland
Hedgehog
Hedgehogs are small mammals that live
in the wild in Europe, Africa, and Asia.
They are also kept as pets in some parts
of the world. People sometimes call porcupines
hedgehogs, but hedgehogs and
porcupines are different animals.
Hedgehogs are found in deserts, forests,
grasslands, marshes, and gardens. They
spend the day sleeping under leaves or in
holes. They come out at night to eat
insects, slugs, spiders, small reptiles, and
fallen fruit.
The hedgehogs called spiny hedgehogs
have thousands of sharp spines on their
bodies. Spines cover everything except
Heather plants grow on a hill in Yorkshire,
England.
There are 15 species, or types, of hedgehog.
The European hedgehog is sometimes
kept as a pet.
BRITANNICA STUDENT ENCYCLOPEDIA Hedgehog 33
the underside, legs, face, and ears. The
spines are cream colored with bands of
brown and black. When threatened,
spiny hedgehogs curl into a ball so that
only their spines are showing. The spines
keep most animals from harming the
hedgehog.
Some spiny hedgehogs hibernate in the
winter. Hibernation allows an animal to
use less energy when food is hard to
find. While hibernating, hedgehogs use
the fat built up in their bodies to survive.
Hairy hedgehogs have hair instead of
spines. They also have well-developed
tails. They look like rats. Their hair
color ranges from white to brownish red
to black. The hair may be soft or very
rough. Hairy hedgehogs can be the size
of a mouse, or they can be as long as 18
inches (46 centimeters).
..More to explore
Hibernation • Mammal • Pet
• Porcupine
Helena
Population
(2007 estimate)
28,726
Helena is the capital of the U.S. state of
Montana. The city is located near the
Missouri River and the Rocky Mountains.
Helena is a center for the trade of crops
and livestock. Many people there work
for the state government. Manufacturing
industries and tourism also bring money
to the city. The Montana Historical
Society is located in Helena. It has a
museum, a library, and an art gallery.
The explorers Meriwether Lewis and
William Clark passed through the Helena
area in 1805. The town was founded
after gold was discovered there in 1864.
The miners had almost given up their
search for gold. Finally they struck gold
in a place they called Last Chance
Gulch. The town was named for Helena,
Minnesota.
Helena became the capital of the Montana
Territory in 1875. Montana became
a U.S. state in 1889. Helena remained
the capital. Earthquakes damaged the
city in the 1930s, but the damage was
quickly repaired.
..More to explore
Lewis and Clark Expedition • Montana
The Montana state Capitol, in Helena, was
opened for use on July 4, 1902.
34 Helena BRITANNICA STUDENT ENCYCLOPEDIA
History
People in China and Europe made toys
that worked like helicopters many hundreds
of years ago. In the 1400s the Italian
artist and engineer Leonardo da
Vinci drew an aircraft much like today’s
helicopters. It was never built. In 1843
the English inventor Sir George Cayley
built a helicopter powered by a steam
