# Who Was Euclid?

Euclid was an ancient Greek mathematician, famous for his work in geometry. His book of geometry, Elements, is one of the most widely read books of all time and has earned Euclid the nickname the Father of Geometry.

# Euclid's Life

Euclid lived in the reign Ptolemy I (323 - 283BC) in the city of Alexandria. He taught at the Great Library.

Little is known of his personal life, but few people's work is so widely known so many years after their death.

# Euclid's Book, Elements

Euclid's book, Elements, is the most successful and widely-used text book of all time.

Elements consist of 13 books, which set out the subject of geometry: the study of points, lines, angles, and shapes.

It contains most of the geometry known at that time and continues to be taught up to the present day. Much of the geometry that students learn at school today comes straight from Euclid's work. Indeed, it wasn't until the 19th century - 2,000 years after Euclid's life - that any geometry not based on Euclid's work was invented!

Euclid did not invent everything in his book, but what is special is the logical and rigorous way he sets out the subject.

# Euclid's Method

Euclid's method follows the following steps:

• He begins with Definitions - e.g. of points, lines, angles, boundaries, circles, squares etc.

• He then has Postulates - e.g. a straight line can be drawn between any two points, and...

• ...Common notions - e.g. things which equal the same thing also equal one another.

• These are the foundation for his Propositions - e.g. if in a triangle two angles equal one another, then the sides opposite the equal angles also equal one another - upon which the rules of geometry are built.

He allows himself the use of a straightedge and a compass, and he builds on previous propositions, to create propositions.
The slider below gives an example of Euclid's method.

It is this logical, step-by-step process which has proved so influential for future mathematicians and scientists.

# Euclid's Other Works

As well as his work on geometry, Euclid also wrote works on ratios, catoptrics (which looks at images in mirrors), optics (about perspective) and on astronomy.

Name: Euclid
Born: Mid 4th Century BC
Died: Mid 3rd Century BC
Famous for: Geometry

# What's in a Name?

Euclid's name in Greek means "reknowned, glorious".

# Elements Facts

Elements has:
• 13 books
• 138 definitions
• 5 postulates
• 5 common notions
• 468 postulates

# Euclid's Fans

Euclid has had many great fans.

Abraham Lincoln kept a copy of Euclid in his saddlebag and would read it late at night by lamplight to aid his career as a lawyer:

"You never can make a lawyer if you do not understand what demonstrate means; and I left my situation in Springfield, went home to my father's house and stayed there till I could give any proposition in the six books of Euclid at sight".

Albert Einstein received a copy when he was a boy and claimed it had a great influence on him. He called Elements the "holy little geometry book".