cised the ingenuity
of the Arabian scholars were astronomy, mathematics, and medicine. The
practical phases of all these subjects were given particular attention.
Thus it is well known that our so-called Arabian numerals date from
this period. The revolutionary effect of these characters, as applied to
practical mathematics, can hardly be overestimated; but it is generally
considered, and in fact was admitted by the Arabs themselves, that these
numerals were really borrowed from the Hindoos, with whom the Arabs came
in contact on the east. Certain of the Hindoo alphabets, notably that of
the Battaks of Sumatra, give us clews to the originals of the numerals.
It does not seem certain, however, that the Hindoos employed these
characters according to the decimal system, which is the prime element
of their importance. Knowledge is not forthcoming as to just when or by
whom such application was made. If this was an Arabic innovation, it was
perhaps the most important one with which that nation is to be credited.
Another mathematical improvement was the introduction into trigonometry
of the sine--the half-chord of the double arc--instead of the chord
of the arc itself which the Greek astronomers had employed. This
improvement was due to the famous Albategnius, whose work in other
fields we shall examine in a moment.

Another evidence of practicality was shown in the Arabian method of
attempting to advance upon Eratosthenes' measurement of the earth.
Instead of trusting to the measurement of angles, the Arabs decided to
measure directly a degree of the earth's surface--or rather two degrees.
Selecting a level plain in Mesopotamia for the experiment, one party
of the surveyors progressed northward, another party southward, from
a given point to the distance of one degree of arc, as determined by
astronomical observations. The result found was fifty-six miles for the
northern degree, and fifty-six and two-third miles for the southern.
Unfortunately, we do not know the precise length of the mile in
question, and therefore cannot be assured as to the accuracy of the
measurement. It is interesting to note, however, that the two degrees
were found of unequal lengths, suggesting that the earth is not a
perfect sphere--a suggestion the validity of which was not to be put
to the test of conclusive measurements until about the close of the
eighteenth century. The Arab measurement was made in the time of Caliph
Abdallah al-Mamun, the son