engine. It could barely get off the
ground.
By the 1900s more powerful engines
were available. Engineers used these
engines to improve the helicopter. They
also made improvements that helped
keep helicopters stable in the air. The
first successful helicopters were built in
Germany in the 1930s. After that, engineers
designed new types of helicopters
that were used for all kinds of different
purposes.
..More to explore
Airplane • Leonardo da Vinci
Helsinki
Population
(2008
estimate), city,
568,531;
(2003
estimate), urban
area,
1,075,000
Helsinki is the capital of Finland, a
country in northern Europe. It is Finland’s
largest city. Helsinki is located on
land that sticks out into a gulf of the
Baltic Sea. The city is surrounded by
good natural harbors.
Helsinki is Finland’s leading port and
center of industry. The city’s main
industries include shipbuilding and
printing. Factories in the city make electronics,
clothing, and metal products.
Most people in Helsinki work in industries
that provide services. Businesses
related to computers, telephones, and
other kinds of technology are important
to the city’s economy.
The king of Sweden founded Helsinki
in 1550. Finland was part of Sweden for
hundreds of years.
In the early 1700s Helsinki suffered
from disease, fire, and attacks by Russian
forces. Russia invaded the city again in
1808. Helsinki was burned to the
ground. Soon all of Finland became part
of Russia.
The Uspenski Cathedral is located in Helsinki.
It is the largest Orthodox church in
western Europe. It was built in the 1860s,
when Russia ruled Finland.
36 Helsinki BRITANNICA STUDENT ENCYCLOPEDIA
The Russian ruler moved the capital of
Finland to Helsinki in 1812. Helsinki
grew rapidly as the new capital. The city
center was completely rebuilt.
In 1917 Finland declared its independence
from Russia. A brief but bloody
war followed in Helsinki. Conditions
soon became more stable. Helsinki
developed into an important center of
trade, industry, and culture.
#More to explore
Finland
Hemisphere
A hemisphere is half of a sphere, or ball.
People use the word to describe one half
of Earth. Geographers, or people who
study Earth, have divided the planet
into two sets of two hemispheres. These
are the Northern and Southern hemispheres
and the Eastern andWestern
hemispheres.
Northern and Southern
Hemispheres
An imaginary line called the equator
divides the Northern and Southern
hemispheres. The equator is also called
0° latitude. It runs east and west around
Earth’s middle. Places north of the
equator are part of the Northern Hemisphere.
Places south of the equator are in
the Southern Hemisphere.
The Northern Hemisphere includes
North America, Central America,
Europe, and mainland Asia. About half
of Africa and a small part of South
America are also in the Northern Hemisphere.
The rest of Africa, most of South
America, and all of Australia and Antarctica
lie in the Southern Hemisphere.
Eastern and Western
Hemispheres
Another imaginary line separates Earth
into Eastern andWestern hemispheres.
On one side of Earth, this line is called
BRITANNICA STUDENT ENCYCLOPEDIA Hemisphere 37
0° longitude, or the prime meridian. It
runs from the North Pole to the South
Pole through western Europe, western
Africa, and the Atlantic Ocean. On the
other side of Earth, the line is called
180° longitude. It runs from the North
Pole to the South Pole through the
Pacific Ocean.
TheWestern Hemisphere lies west of 0°
longitude and east of 180° longitude. It
includes North America and South
America. The Eastern Hemisphere lies
east of 0° longitude and west of 180°
longitude. It includes almost all of
Europe and Africa and all of Asia and
Australia. About half of Antarctica lies in
the Eastern Hemisphere, and about half
lies in theWestern Hemisphere.
#More to explore
Equator • Latitude and Longitude
Hemlock
Hemlocks are tall evergreen trees in the
pine family. There are about 10 species,
or types, of hemlock found in North
America and eastern Asia. Hemlocks
grow slowly and can live for 800 years or
more.
Hemlocks grow best in cool, shaded
areas. They grow to an average height of
60 to 70 feet (18 to 21 meters) but can
be much taller. They have drooping
branches that form the shape of a pyramid.
Small cones hang from the branch
tips. The cones hold the tree’s seeds. The
leaves, called needles, are short and flat.
Insects eat the needles and can destroy
whole forests of hemlocks.
The bark of hemlock trees provides tannin.
Tannin is used to preserve and dye
leather. People also make paper out of
hemlock wood.
Some poisonous plants also are called
hemlock, but they are not related to
hemlock trees. They include poison
hemlock and water hemlock. These
plants are poisonous herbs of the parsley
family. They grow in North America
and Europe. Animals and people can die
from eating these plants.
#More to explore
Herb • Pine • Tree
Henry VIII
England had eight kings named Henry.
The last of them, Henry VIII, is remembered
for his six wives and his quarrel
with the Roman Catholic church.
Seawater covers
about 80
percent of the
Southern
Hemisphere. It
covers about
60 percent of
the Northern
Hemisphere.
