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