Prince Henry the Navigator (1394–1460) was a prince from Portugal, the third son of King John I of Portugal. He was called Infante Dom Henrique in Portuguese. He was never a navigator himself. He got his name because he organized many ocean voyages on which lands were found. He is seen as the man who started the Age of Discovery. He also opened a navigation school in Portugal, so the technology of tools and ships could be made better. His explorers discovered the first shipping routes directly from Europe to Asia for the Portuguese monarchy.
Concrete
Concrete is an important material for making different buildings and structures. It is a composite made of Portland cement, sand, gravel or aggregate, and water in varying proportions depending on the task.
Concrete is used more than any other man-made material in the world. As of 2006, about 7.5 billion cubic meters of concrete are made each year—more than one cubic meter for every person on Earth.
The ingredients are mixed together into a paste, a bit like making dough for bread. The concrete is then poured into a frame. After a few hours it sets hard. Concrete solidifies due to a chemical reaction known as hydration. The water reacts with the cement, which bonds the other components together, eventually creating a strong stone-like material.
Concrete is used to make pavements, pipe, architectural structures, foundations, motorways, bridges, multi-story parking, walls, footings for gates, fences and poles and even boats.
Its biggest advantage is that it bonds together bricks and stones better than any other method known to mankind.
Concrete is strong in compression but weak in tension. For some purposes it needs to be reinforced with steel rods. Reinforced concrete buildings can be made to link all the parts together, the foundations, walls, floors and roofs, but concrete construction does not make buildings earthquake-proof.
Concrete is as old as 5600 BC. It was not invented by Romans, but much used by them. Some kinds of concrete are waterproof, and some kinds even set underwater.
There are many additives to make concrete set faster, set slower, set stronger, reduce corrosion and so on. The Romans discovered that adding volcanic ash produced a concrete which would set under water. The Romans also knew that adding horse hair made concrete less liable to crack as it set, and that adding blood made it more frost-resistant.
Modern concrete was made in 1756 by British engineer John Smeaton. He added pebbles and powdered brick to the cement. In 1824, English inventor Joseph Aspdin invented Portland cement, which has remained the main cement used in concrete production. He burnt ground-up limestone and clay together. The burning process changed the chemical properties of the materials and Aspdin created a stronger cement than plain crushed limestone alone could produce.
The 19th century saw the invention of reinforced concrete by French gardener Joseph Monier in 1849 (patented in 1867). François Coignet studied and improved it. This is concrete with steel bars in it, called rebars (reinforcing bars). Glass fibre or plastic fibre is beginning to replace steel bars.
Many modern chemicals can be added to the mixture to achieve special objectives. 'Superplasticizers' are chemicals which improve workability, which means the ability to shape the concrete before it has set. Pigments can change the dull grey colour. Corrosion inhibitors can reduce rusting on the steel bars. 'Air entrainment' is blowing little bubbles in the concrete before it sets. This helps the concrete survive the freezing and thawing of a cold climate. Blast furnace slag can be mixed with concrete. It turns the colour into almost pure white and makes the concrete stronger.
Marathon
A marathon is a long distance running sport event where an athlete must run 42.195 kilometres (26 miles and 385 yards). There are many marathons held all over the world each year. It is a very difficult event and runners are advised to run many miles before they compete. This event was named after a battle of the Greco-Persian wars.
The famous battle of Marathon was fought in 490 B.C. An army from Persia came to fight the army of Athens. The army from Athens was not expected to win, but they did. After the victory, they sent their best runner, a man named Pheidippides back to Athens to tell everyone the good news. He ran about 25 miles and died of exhaustion when he arrived.
In 1896 the first modern Olympics was held. There was a race called the Marathon there. It was only about 25 miles (40 km) then.
Holy Roman Empire
The Holy Roman Empire (; ), occasionally but unofficially referred to as the Holy Roman Empire of the German Nation, was a group of regions and free cities in central Europe which all came under the rule of an emperor who was elected by the princes and magistrates of the regions and cities within the empire. When Charlemagne died, his Frankish Empire was given to his children and divided into three different countries: West Francia, Lotharingia and East Francia. The Holy Empire started when Otto I of East Francia became emperor in 962, and it was ended by Napoleon in 1806. The emperors claimed to be heirs of Charlemagne and that the Empire dates from 800, when Charlemagne became Frankish Emperor.
In the 16th century the Holy Roman Empire (HRE) had to deal with the rebellion of the Frisians lead by Pier Gerlofs Donia and Wijerd Jelckama. This lasted from 1515 until 1523.
In the 17th century the Empire was shattered by the Thirty Years' War (1618-1648). Nearly thirty percent of the population of the Empire was killed. The "Holy Roman Empire of the German Nation" lost parts of its territory.
Until the 13th century, the Holy Roman Empire was powerful. Later, all the duchies and counties inside the Empire started to get more power. At the end, the emperors had little real power anymore, and the country existed only in name. The last emperor abolished the empire in 1806 during the Napoleonic Wars.
Voltaire, a French philosopher in the 18th century, once joked that the nation was neither holy, nor Roman, nor an empire.
The Empire was in fact Germanic and not Roman since it was mainly in the regions of present-day Germany and Austria. It was not really holy since, after Charles V in 1530, no emperors were crowned by the Pope. It was only really an Empire by name: the territories it covered were mostly independent. The Empire had its own central government and armed forces that acted as one. It was ruled by the House of Habsburg before that fell in 1806. Napoleon forced the emperor to abdicate when France began invading the Holy Roman Empire during the First French Empire. The Emperor made himself emperor of Austria and ended the Holy Roman Empire.
The Holy Roman Empire was not a highly centralized state like most countries today. Instead, it was divided into dozens – eventually hundreds – of individual entities governed by kings, dukes, counts, bishops, abbots, and other rulers. They were collectively known as princes. The Emperor directly ruled some areas. At no time could the Emperor simply issue decrees and govern autonomously over the Empire. His power was severely restricted by the various local leaders.
The Empire was one of the rare countries in Europe that had an elective monarchy. This meant that the Emperor was chosen by a small group of Prince-electors. Common practice was to just elect the deceased Emperor or Empress 's heir to the throne.
Notes
Friesland
Friesland (Fryslân in West Frisian, Friesland in Dutch) is a province in the north of the Netherlands. The capital (city) of Friesland is Leeuwarden ("Ljouwert" in Frisian). People in Friesland speak West Frisian and Dutch. People also speak Frisian in a small part of Groningen (province), and in East Friesland and North Friesland in Germany. In North Holland there is a region called West Friesland, but people who live there are not called Frisians.