beams create a pattern of closely
spaced lines. The pattern recorded on
the film is the hologram.
Some types of hologram have to be
viewed with light from a laser. Other
holograms can be viewed with ordinary
light.
Holograms have many uses. People can
make holograms of things that are hard
to see normally—for example, parts
inside the human body. Then they can
study the details recorded in the hologram.
Small holograms are commonly
found on credit cards, driver’s licenses,
and paper money. The holograms make
it difficult to produce illegal copies.
#More to explore
Laser • Photography
Holy Roman
Empire
For many centuries, beginning in AD
800, the Holy Roman Empire ruled
Holography uses no camera. Instead, two beams of light from a single laser shine on a
piece of film. One of the beams reflects from the object.
BRITANNICA STUDENT ENCYCLOPEDIA Holy Roman Empire 73
over much of Europe. The lands of the
empire originally included what are
now Germany, Austria, the Czech
Republic, Switzerland, The
Netherlands, Belgium, Luxembourg,
eastern France, and parts of northern
and central Italy.
In its later centuries the Holy Roman
Empire lost most of its power. Nevertheless,
it lasted for more than 1,000 years,
until 1806.
Beginnings
The western part of the Roman Empire
came to an end in AD 476. The Roman
Empire continued in the east as the Byzantine
Empire. It was ruled from Constantinople,
in what is now Turkey.
In the place of the western empire rose
many tribal kingdoms. One of the tribes
was the Franks. The modern country of
France is named after the Franks. A
Frankish ruler named Charlemagne conquered
surrounding lands and became
very powerful. In 800 Pope Leo III, the
head of the Roman Catholic church,
crowned Charlemagne emperor of the
new Roman Empire.
The pope wanted a strong new empire
with close ties to the church. However,
soon after Charlemagne’s death the
empire broke apart. The western part
became known as France. The eastern
part became known as Germany. It continued
the empire.
The title of emperor did not pass automatically
from father to son. Local German
rulers elected a German king. If the
Rudolf I was Holy Roman
emperor from 1273 to 1291.
An illustration shows the crowning of
Emperor Louis I (right). Louis was the son of
Charlemagne. Many rebellions broke out
during Louis’s reign.
74 Holy Roman Empire BRITANNICA STUDENT ENCYCLOPEDIA
pope agreed with the choice, he crowned
the king emperor.
Saxon Emperors
By the middle of the 900s, a German
people called the Saxons ruled the
empire. The Saxon emperor Otto III,
who reigned between 983 and 1002,
made Rome his capital. For a long time
afterward, popes and emperors quarreled
over who had the right to choose religious
leaders.
Hohenstaufen Emperors
Emperors of the Hohenstaufen family
gained power in 1138. The Hohenstaufen
emperor Frederick I Barbarossa
added the word holy to the name of the
empire. This was because he wanted to
have as much respect as the pope had.
Frederick died in 1190. Not long after
that, the empire lost some of its earlier
importance.
Hapsburg Emperors
In 1273 the Hapsburg family gained
control of Germany. They soon centered
their power in Austria. Hapsburg kings
often took the title of emperor without
being crowned by the pope. The Hapsburgs
ruled the Holy Roman Empire
almost continuously from 1452 onward.
End of the Empire
In the 1500s some people broke away
from the Roman Catholic church and
formed Protestant churches. This weakened
the empire. German leaders who
became Protestant opposed the Roman
Catholic emperors.
After about 1650 the empire was only a
loose grouping of German states. In
1806 Emperor Francis II finally ended
the Holy Roman Empire. Francis continued
to rule, however, as emperor of
Austria.
#More to explore
Charlemagne • Germany • Hapsburgs
• Roman Catholicism
Holy See
#see Vatican City.
Homeopathy
Homeopathy is a form of medical care.
It is based on the idea that “like cures
like.” This means that a drug that creates
symptoms, or signs, of illness in a
Homeopathy is popular in many parts of
the world. A store in Hong Kong has
shelves full of homeopathic medicines.
BRITANNICA STUDENT ENCYCLOPEDIA Homeopathy 75
healthy person can be used to treat the
same symptoms in a sick person.
Homeopathy started with German physician
Samuel Hahnemann in 1796.
Hahnemann did an experiment on himself.
He took large doses of a drug to
treat the disease malaria. He went from
healthy to having symptoms of malaria.
This gave him the idea of “like cures
like.”
Hahnemann also thought that large
doses of medicine made an illness worse.
He believed that small doses were more
effective. This idea is also a part of
homeopathy.
Before homeopathy, doctors sometimes
treated patients with methods that were
harsh and even dangerous. For example,
they might draw a lot of blood from a
person’s body while trying to cure a
disease. Homeopathy became popular
because it was a milder form of treatment.
But today many doctors dislike
homeopathy. They prefer to look for the
cause of an illness instead of focusing on
the symptoms.
#More to explore
Drug • Medicine
Homer
