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The Golden Section
As mentioned before, Golden Section is a geometrical
proportion that was commonly know in antiquity, even though it had a
different name. About 300BC Euclid of Alexandria described the proportion
in this Elements and called it the division in extreme and mean ratio. The
geometrical description is a line AB divided by point C in such a way that
the shorter part (AC) relates to the longer part (CB) in the same way as
the longer part (CB) relates to the entire line (AB)

Euclid's illustration of the line divided in extreme and
mean ratio proves that at least from this moment onwards, Greeks, Jews and
later Romans were publicly aware of the mathematical qualities of the
Golden Section proportion. In this case Jews are especially mentioned
because Alexandria, hometown of Euclid, housed a large Jewish community
that later brought forth the famous Jewish philosopher and historian Philo
of Alexandria. Apart from Euclid and Philo, also Archimedes and the
Jewish/Christian church-founder Origenes lived in Alexandria.
As mentioned before, an irrational number is connected
to the proportoin of the Golden Section. In the example above this means
that AC relates to CB and CB to AB like 1:(1+√5)/2
which is approximately
1,61803398875 …
The Fibonacci Series
Besides a geometric approach, the Golden Section can
also be constructed by means of the well known progressive number series
of Leonardo Fibonacci of Pisa.
At the end of the twelfth century, the now
famous Italian mathematician Leonardo Fibonacci returned to his hometown
Pisa after a long stay in North Africa and the Middle East. During his
absence Fibonacci studied various mathematical systems unknown in Europe.
After his return, Fibonacci worked for years on various mathematical
masterpieces. In his famous “Liber Abbaci” he describes how rabbit
populations multiply themselves mathematically. This sequence has become
known as the series of Fibonacci.
The series is easily constructed by adding up two numbers starting from
one, while the outcome is consequently added to the number that came
immediately before. The series starts from zero and one:
0+1 =
1
1+1 =
2
1+2 =
3
2+3 =
5
3+5 =
8
5+8 =
13
8+13 =
21
13+21 =
34
21+34 =
55
34+55 =
89
55+89 =
144
etc.
In the illustration below it is possible to see how the
Fibonacci series can be used to construct a rectangle according to the
proportions of the Golden Section. The construction starts with a very
small square with dimensions 1x1. Length and width are added up, using
this new length to draw a bigger rectangle which more and more approaches
the 1:1,618 proportion of the Golden Section.

A Fibonacci rectangle is buildup of an
ever expanding series of squares.
The increasing accuracy of the "Fibonacci Rectangle" is
illustrated in the table below. As one can see, even the lower Fibonacci
numbers already produce a fairy accurate Golden Section rectangle.
Dividing 89 by 55 gives a result that is accurate to three digits.

The Fibonacci series produces a
accurate approach to
the Golden Section Proportion. 1 : (1+√5)/2 ≈
1,618 033 988 75 …
The twentieth Fibonacci number is accurate to seven
digits and after the thirtieth number result is already accurate to an
astonishing 11 digits. With unlimitedly growing Fibonacci numbers,
accuracy will also grow unlimitedly even though it will never become 100%
accurate, just as the mathematical formula 1:(1+√5)/2
will never produce an accurate number. The Golden Section will always
remain a purely geometric proportion which can not be expressed by means
of a natural number. The only approximate approach by means of natural
numbers is provided by the Fibonacci series.
The previous chapters have provided examples of
geometrical figures that are based on the Golden Section, of which the
pentagram probably the most impressive. Inside each pentagram resides a
small pentagon, in which a new smaller pentagram can be drawn. The smaller
pentagrams relate to the bigger ones like
1:(1+√5)/2 in the same way as progressive Fibonacci
numbers do. This remarkable quality
to grow in a progressive numerical or geometrical way without ever losing
the original proportions of its "extreme and mean ratio" is a unique
feature of the Golden Section that must have appealed enormously to
classical scholars.
The
√2 proportion
Besides the Golden section there was only one proportion
that had the same kind of geometrical features as the Golden Section and
that is the 1:√2 proportion described by
Vitruvius in his ten books on architecture.

The Golden Section & the
√2 proportion.
Just like with the Golden Section. the
√2 proportion creates a basic rectangle that is easily constructed. This
rectangle measures approximately 1:1,414 213 562 373 and can easily be
enlarged without losing its proportion by doubling the width of the
original rectangle and using this as the length of a new rectangle as
illustrated below.

A 1:√2 rectangle can be doubled or divided in two
without altering its proportions.
The √2 proportion has been used in
architecture on vast scale during antiquity. There is no doubt that this
architectonic interest was due to the fact that is is very easy to
construct buildings by means of √2
because spaces can be doubled or divided without alternating their
proportion. In our time, √2 is still used on a daily
basis. The famous A4 paper size on which the whole
of Europe makes its photocopies and prints its documents is based on the
1:√2 proportion. Folding an A4 sheet of paper in two crates an A5, while two
A4's together create an A3 size sheet. Each A-format paper sheet is a
rectangle based on the 1:√2 proportion. It looks very simple but only √2
rectangles have this beautiful geometric quality.

The European
A-format paper system is based on the √2 proportion.
The basic A0 size has a surface of 1 square meter.
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