The Victorians built many train systems in the mid-19th century (1850s). Their main stations are in London, and the lines go to every part of Great Britain. There were originally five major companies but the five companies became a national rail network in modern times.
There are five airports, though only one is actually in London (London City Airport). There is the London end of the LondonBirmingham canal, which was important to the industrial 19th century. The most used airport is Heathrow International Airport although it is actually outside the city.
The metro or London Underground is a system of electric trains which are in London. It is the oldest underground railway in the world. It started running in 1863 as the "Metropolitan Railway". After the opening the system was copied in many other cities, for example New York and Madrid. Even though it is called "the Underground" about half of it is above the ground. The "Tube" is a slang name for the London Underground, because the tunnels for some of the lines are round tubes running through the ground. The Underground has got 274 stations and over 408 km of track. From 2006–2007 over 1 billion passengers used the underground.
Litre
A litre (international spelling) or liter (American spelling) is one of the metric units of volume. It is not a basic SI unit, but it is a supplementary unit.
One litre is the volume of 1000 cubic centimetres, that is a cube of 10 × 10 × 10 centimetres (1000 cm). One litre of water at has the mass of exactly one kilogram. This results from the definition given in 1795, where the gram was defined as the weight of one cubic centimetre of melting ice.
The symbol for litre is l or ℓ.
For smaller volumes, the decilitre is used: 10 dl = one litre.
For smaller volumes, the centilitre is used: 100 cl = one litre.
For smaller volumes, the millilitre is used: 1000 ml = one litre.
The capital letter "L" is preferred by some people as the small "l" can look like the number one "1".
The metric system was first introduced in France in 1791. That system did not have its own unit of capacity or volume because volume can be measured in cubic metres. In 1793 work to make the metric system compulsory in France was started by the Temporary Commission of Republican Weights and Measures. Due to public demand, the commission said that the cubic metre was too big for everyday use. They said that a new unit based on the old cadil should be used instead. One cadil was to be 0.001 cubic metres. This was equivalent to a cube with sides 10 cm. The "cadil" was also known as the "pinte" or the "litron". The "pinte" had been an old French unit of measure of capacity. In 1795 the definition was revised. The "cadil" was given the name "litre".
In 1795 the kilogram was defined to be exactly one litre of water at 4 °C. In 1799 the kilogram was redefined. The new definition said that the kilogram was the mass of the "kilogram des archives". In 1901 scientists measured the volume of one litre of water at 4 °C very carefully. They found that it occupied about  dm. The BIPM redefined the litre as being "exactly" the volume of one kilogram of water at 4 °C.
In 1960 the SI was introduced. The BIPM changed the definition of the litre back to "one dm". The litre is not part of SI. The BIPM defined the litre as a "Non-SI unit accepted for use with the SI". This was because it is used in many countries. The BIPM said that the litre should not be used for very accurate work.
According to SI rules, the symbol for the litre should be "l". This is because the litre was not named after somebody whose name was "Litre". However the symbol "l" and the number "1" are easily confused. In 1979 the BIPM made an exception for the symbol for the litre. They said that people could use either "L" or "l" as its symbol.
In Europe, milk is sold in one litre cartons. One litre bottle is also a popular package for soft drinks. Most alcoholic drinks are sold as 1/3 litre (0.33 l), ½ litre (0.5 l) or 3/4 litre (0.75 l) bottles.
Lime
Lime is a green fruit, and the tree fruit itself. They are citrus fruits similar to lemons. Limes are rich in vitamin C. Sailors from Britain were given lemon or lime juice to stop them falling ill with scurvy. This is how they got the nickname "Limey". There are several citrus trees whose fruits are called limes. They include the key lime "Citrus aurantiifolia", the Persian lime, the kaffir lime, and the desert lime "Citrus glauca".
Limes are small, round and bright green. If they stay on the tree for a long time they turn yellow. Then they look like small round lemons.
Lime juice is used in cooking and in drinks. Lime oils are often used in perfumes, used for cleaning, and used for aromatherapy.
Lime tastes acidic and bitter. Lime juice is also made from limes.
Mathematics
Mathematics is the study of numbers, shapes and patterns. The word comes from the Greek word "μάθημα" (máthema), meaning "science, knowledge, or learning", and is sometimes shortened to maths (in England, Australia, Ireland, and New Zealand) or math (in the United States and Canada). The short words are often used for arithmetic, geometry or simple algebra by students and their schools.
Mathematics includes the study of:
Mathematics is useful for solving problems that occur in the real world, so many people besides mathematicians study and use mathematics. Today, some mathematics is needed in many jobs. People working in business, science, engineering, and construction need some knowledge of mathematics.
Mathematics solves problems by using logic. One of the main tools of logic used by mathematicians is deduction. Deduction is a special way of thinking to discover and prove new truths using old truths. To a mathematician, the reason something is true (called a proof) is just as important as the fact that it is true, and this reason is often found using deduction. Using deduction is what makes mathematics thinking different from other kinds of scientific thinking, which might rely on experiments or on interviews.
Logic and reasoning are used by mathematicians to create general rules, which are an important part of mathematics. These rules leave out information that is not important so that a single rule can cover many situations. By finding general rules, mathematics solves many problems at the same time as these rules can be used on other problems. These rules can be called theorems (if they have been proved) or conjectures (if it is not known if they are true yet). Most mathematicians use non-logical and creative reasoning in order to find a logical proof.
Sometimes, mathematics finds and studies rules or ideas that we don't understand yet. Often in mathematics, ideas and rules are chosen because they are considered simple or neat. On the other hand, sometimes these ideas and rules are found in the real world after they are studied in mathematics; this has happened many times in the past. In general, studying the rules and ideas of mathematics can help us understand the world better. Some examples of math problems are addition, subtraction, multiplication, division, calculus, fractions and decimals. Algebra problems are solved by evaluating certain variables. A calculator answers every math problem in the four basic arithmetic operations.
These theorems have interested mathematicians and people who are not mathematicians.
These are theorems and conjectures that have greatly changed mathematics.
Progress in understanding the nature of mathematics also influences the way mathematicians study their subject.
Mathematics in history, and the history of mathematics.
There is no Nobel prize in mathematics. Mathematicians can receive the Abel prize and the Fields Medal for important works.
The Clay Mathematics Institute has said it will give one million dollars to anyone who solves one of the Millennium Prize Problems.
There are many tools that are used to do mathematics or to find answers to mathematics problems.
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