Britannica Student Encyclopedia - 2010

polio. Vaccines have also been developed

for mumps, measles, cholera, plague,

tuberculosis, influenza, and hepatitis.

#More to explore

Disease, Human • Immune System

• Pasteur, Louis • Salk, Jonas

Vacuum

A vacuum is a space with nothing in

it—not even air. On Earth there is no

such thing as a total vacuum because it

is impossible to remove all the air from a

A child gets a shot containing a vaccine to

protect her against disease.

BRITANNICA STUDENT ENCYCLOPEDIA Vacuum 49

 

space. But partial vacuums are common.

A partial vacuum is a space with almost

no air inside.

Vacuums do not exist naturally on

Earth. Air surrounds everything on

Earth, and it extends for miles above

Earth. All of the air above Earth is pushing

down all the time. This is known as

air pressure. Because of the pressure, air

will try to fill any space. In outer space,

however, there is no air, so all of outer

space is a giant vacuum. That is why

astronauts must wear space suits. The

suits hold in air at the pressure that

humans are used to on Earth. Otherwise

their bodies would not function.

A partial vacuum can be made on Earth

by removing all solids and liquids and

then pumping air out of a container or

some other enclosed space. Vacuums

have many uses. A vacuum cleaner picks

up dirt by sucking air into a vacuum. A

medicine dropper creates a vacuum to

suck liquid into a tube. A vacuum

bottle, or Thermos, is a container with a

double wall. A vacuum between the

walls stops heat from flowing to or from

the outside air. This helps keep the liquid

inside cold or warm. Vacuums are

useful in industry, too. For example,

food companies use vacuum packaging

to help keep food from spoiling.

..More to explore

Air

Vaduz

Population

(2008 estimate)

5,110

Vaduz is the capital of Liechtenstein, a

country in central Europe. The town lies

in the Rhine River valley. It is Liechtenstein’s

cultural center. The castle of the

ruling prince of Liechtenstein overlooks

the town.

Tourism is important to the economy of

Vaduz. Small factories in the town make

high-technology equipment and other

products.

Vaduz dates back to at least the 1300s.

The town was destroyed in 1499 in a

war between Switzerland and the Holy

Roman Empire. Vaduz was rebuilt in the

early 1500s. It became a state within the

Holy Roman Empire.

In 1719 Vaduz was combined with a

state called Schellenberg to form Liechtenstein.

The Holy Roman Empire

Vacuum packing helps keep foods fresh. existed until 1806. Then Liechtenstein

50 Vaduz BRITANNICA STUDENT ENCYCLOPEDIA

 

became a German state. In 1866 it

became an independent country with

Vaduz as its capital.

#More to explore

Liechtenstein

Valentine’s Day

Valentine’s Day is a holiday that people

celebrate on February 14. It is also called

Saint Valentine’s Day. On Valentine’s

Day people greet loved ones, close

friends, family members, and school

classmates by sending them cards called

valentines. People also give candy, flowers,

and other gifts to loved ones. Valentine’s

Day gifts often come packed in a

red, heart-shaped box.

People have celebrated Valentine’s Day

with thoughts of love since at least the

1300s. According to an old European

legend, February 14 is the day when

birds pair off each year to start their new

families. February 14 is called Valentine’s

Day because the Roman Catholic

church honors two saints named Valentine

on that day. Both Saint Valentines

were ancient Romans of the AD 200s

who died for their Christian faith.

Groups of young men and women once

celebrated Valentine’s Day by picking up

valentines from a box. The person whose

valentine was picked up would become

the picker’s “valentine” for a year.

#More to explore

Festival and Holiday

Valhalla

In the tales of the Vikings and other

early people of Scandinavia, Valhalla was

a heaven for warriors. Scandinavia is a

region of northern Europe. Its tales are

known as Norse mythology.

According to the tales, Valhalla was a

vast banquet hall. It had at least 540

doors and a roof made of shields. The

powerful Norse god Odin ruled over

Valhalla. He allowed only warriors who

had died bravely to go there.

Female spirits called Valkyries watched

over battlefields. They brought dead

heroes to Valhalla. The warriors of Valhalla

ate the flesh of a boar (pig) that

was butchered every day and then magically

came back to life.

It was said that the dead warriors would

enjoy Valhalla until the end of the

world. Then they would rise again to

fight against evil giants and demons in a

final battle called Ragnarok.

#More to explore

Odin • Vikings

The prince of Liechtenstein lives in Vaduz

Castle in Vaduz, Liechtenstein.

The slain warriors

who lived

in Valhalla

were called

the Einherjar.

BRITANNICA STUDENT ENCYCLOPEDIA Valhalla 51

 

Valletta

Population

(2005

estimate), city,

6,300; urban

area, 81,050

Valletta is the capital of Malta, an island

country in the Mediterranean Sea. The

city is on the coast of the country’s largest

island, which is also named Malta.

Valletta lies on a piece of rocky land that

sticks out into a bay.

Trade and tourism are important to the

economy of Valletta. It is one of the

country’s main ports.

A group of Roman Catholic knights