athematician to come to Bagdad to impart to him a portion of his
learning, pledging his word that he would restore him quickly and safely
again. "Do not," says the high-minded khalif, "let diversity of religion
or of country cause you to refuse my request. Do what friendship would
concede to a friend. In return, I offer you a hundred weight of gold, a
perpetual alliance and peace." True to the instincts of his race and the
traditions of his city, the Byzantine sourly and insolently refused the
request, saying that "the learning which had illustrated the Roman name
should never be imparted to a barbarian."

[Sidenote: Their great improvements in arithmetic.] From the Hindus the
Arabs learned arithmetic, especially that valuable invention termed by
us the Arabic numerals, but honourably ascribed by them to its proper
source, under the designation of "Indian numerals." They also entitled
their treatises on the subject "Systems of Indian Arithmetic." This
admirable notation by nine digits and cipher occasioned a complete
revolution in arithmetical computations. As in the case of so many other
things, the Arab impress is upon it; our word cipher, and its
derivatives, ciphering, etc., recall the Arabic word tsaphara or ciphra,
the name for the 0, and meaning that which is blank or void. Mohammed
Ben Musa, said to be the earliest of the Saracen authors on algebra, and
who made the great improvement of substituting sines for chords in
trigonometry, wrote also on this Indian system. He lived at the end of
the ninth century; before the end of the tenth it was in common use
among the African and Spanish mathematicians. Ebn Junis, A.D. 1008, used
it in his astronomical works. From Spain it passed into Italy, its
singular advantage in commercial computation causing it to be eagerly
adopted in the great trading cities. We still use the word algorithm in
reference to calculations. The study of algebra was intently cultivated
among the Arabs, who gave it the name it bears. Ben Musa, just referred
to, was the inventor of the common method of solving quadratic
equations. [Sidenote: Their astronomical discoveries.] In the
application of mathematics to astronomy and physics they had been long
distinguished. Almaimon had determined with considerable accuracy the
obliquity of the ecliptic. His result, with those of some other Saracen
astronomers, is as follows:

A.D. 830. Almaimon 23 deg. 35' 52"

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