Bīrūnī, Muḥammad ibn Aḥmad, Alberuni's India (v. 2)

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



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CHAPTER LIII.                              53

Add 38 to the lower number and multiply the sum by
II. Divide the product by 703, and subtract the quo¬
tient from the upper number. The remainder in the
upper place is the number of the civil days, and the
remainder in the lower place is the number of the
avctmas. Add i to the number of days and divide the
sum by 7. The remainder shows the day of the week
on which the date in question falls."

This method would be correct if the months of the
seventy-two years with which the calculation begins
were lunar. However, they are solar months, in which
nearly twenty-seven months must be intercalated,
so that these seventy-two years are more than 864

We shall again exemplify this method in the case of Application
our gauge-date, i.e. the beginning of Eabi' I., A.ii. 422. method to
Between the above-mentioned ist of Sha'ban and the date^^"^^
latter date there have elapsed 2695 months.    Adding
these to the number of months adopted by the author
of the method (864), you get the sum of 3559 months.
Write   down  this  number  in  two  places.    Multiply
the one by 7,  and divide the product by 228.    The
quotient represents   the  ctdhimdsa   months,  viz.   109. Rage 229.
Add them to the number in the other place, and you
get the sum 3668.    Multiply it by 30, and you get the
product  110,040.    Write   down this  number  in two
different places.    Add to the lower number 38, and
you  get 110,078.    Multiply it by  11  and divide the
product by 703.    The quotient is 1722 and a remain¬
der of 292, i.e. the ctvctmas.    Subtract the quotient from
the upper number, and the remainder, 108,318, repre¬
sents the civil days.

This method is to be amended in the following way : Emendation
You must know that between the epoch of the era here method.
used and the first of Sha'ban, here adopted as a date,
there have elapsed 25,958 days, i.e. 876 Arabic months,
or seventy-three years and two months.    If we further
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