Bīrūnī, Muḥammad ibn Aḥmad, Alberuni's India (v. 1)

(London :  Kegan Paul, Trench, Trübner & Co.,  1910.)



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314                        ALBERUNPS INDIA.

these day-minutes by the circumference of the earth,
and divides the product by 6o, viz. the minutes (or
6oth parts) of the daily revolution. The quotient,
then, is the number of the yojanas of the distance
between the two places.

This calculation is correct. The result refers to the
great circle on which Lahka lies.

Brahmagupta calculates in the same  manner, save
that he  multiplies by 4800.    The other details have
already been mentioned.
Calculation      As far as this, one clearly recognises what the Hindu
deidn^tara     astrouomers aim at, be their method correct or faulty,
Aifazart^ ° Howcvcr, WO caunot say the same of their calculation of
the desdntara from the latitudes of two different places,
which is reported by Alfazari in his canon in the fol¬
lowing manner :—

" Add together the squares of the sines of the lati¬
tudes of the two places, and take the root of the sum.
This root is the portio.

"Further, square the difference of these two sines
and add it to the portio. Multiply the sum by 8 and
divide the product by 377, The quotient, then, is the
distance between the two places, that is to say, according
to a rough calculation.

" Further, multiply the difference between the two
latitudes by the yojctnas of the circumference of the
earth and divide the product by 360."

Evidently this latter calculation is nothing but the
transferring of the difference between the two latitudes
from the measure of degrees and minutes to the mea¬
sure of yojanas.    Then he proceeds :—

" Now the square of the quotient is subtracted from
the square of the roughly calculated distance, and of
the remainder you take the root, which represents the
straight yojanas.'"
Page 162,          Evidently the latter number represents the distance

between the spheres of the meridians of the two places
  Page 314