We know little of **Al-Jawhari**'s
life except that he was associated with the
remarkable House of Wisdom that was set up in
Baghdad by the Caliph al-Ma'mun. It is worth
looking at the events which led up to the
founding of this important centre for learning.

Harun al-Rashid became the fifth Caliph of the Abbasid dynasty on 14 September 786, and ruled from his court in the capital city of Baghdad over the Islam empire which stretched from the Mediterranean to India. He brought culture to his court and tried to establish the intellectual disciplines which at that time were not flourishing in the Arabic world. He had two sons, the eldest was al-Amin while the younger was al-Ma'mun. Harun died in 809 and there was an armed conflict between the brothers.

Al-Ma'mun won the armed struggle and al-Amin was defeated and killed in 813. Following this, al-Ma'mun became Caliph and ruled the empire from Baghdad. He continued the patronage of learning started by his father and founded an academy called the House of Wisdom where Greek philosophical and scientific works were translated. He also built up a library of manuscripts, the first major library to be set up since that at Alexandria, collecting important works from Byzantium. In addition to the House of Wisdom, al-Ma'mun set up observatories in which Muslim astronomers could build on the knowledge acquired by earlier peoples.

Al-Jawhari was employed in the service of al-Ma'mun in Baghdad, although we do not know exactly when he began his work there. Mathematicians such as al-Kindi, al-Khwarizmi, Hunayn ibn Ishaq, Thabit ibn Qurra and the Banu Musa brothers were also appointed by al-Ma'mun to the House of Wisdom, so a truly remarkable collection of scholars worked there. There are very few instances in the history of mathematics when a larger number of world class mathematicians gathered together and took part in research. Al-Jawhari, although best known as a geometer, made observations in Baghdad from 829 to 830 while working for al-Ma'mun. He left Baghdad before the death of al-Ma'mun in 833, for he was observing in Damascus in 832-33.

The main work by al-Jawhari was
*Commentary on Euclid's Elements* which is
listed in the *Fihrist* (Index), a work
compiled by the bookseller Ibn an-Nadim in 988.
*Commentary on Euclid's Elements* is almost
the same work described by Nasir al-din al-Tusi
(although al-Tusi gives a slightly different
title for al-Jawhari's work: *Emendation of
the Elements*). This work contained nearly
fifty propositions additional to those given by
Euclid and included an attempt by al-Jawhari to
prove the parallel postulate. The proof followed
similar lines to that attempted by Simplicius
but it is certainly not a copy of Simplicius's
proof, containing several original ideas. Al-Tusi
quotes six of the nearly fifty propositions
which together form what al-Jawhari believed was
a proof of the parallel postulate. This means
that, as far as we are aware, al-Jawhari was the
first Arabic mathematician to attempt such a
proof. The fact that the proof fails was
certainly noted by al-Tusi.

The paper [3] discusses a
thirteenth century commentary on a short
treatise by al-Jawhari. In the short treatise
al-Jawhari presents three additions to Book V of
Euclid's *Elements,* which are meant prove
Definition 5 which defines equal ratio, and
Definition 7 which defines greater ratio. Al-Jawhari's
"proofs" are examples of early attempts by
Muslim mathematicians to understand the
difficult concepts in Euclid's *Elements.*
Berggren, reviewing [3], expresses surprise, not
at al-Jawhari's fallacious arguments, but rather
the fact that they were still being repeated 400
years later:-

One can only wonder, however, at the survival of such ill-conceived alterations of Euclid's "Elements" and their incorporation, so many centuries later, in an Arabic edition of the "Elements" composed late in the thirteenth century.

**Article
by:** *J J O'Connor*
and *E F Robertson*

**November
1999**