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

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

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GHAPTEE  LIII.

ON THE AHAEGANA, OE THE RESOF.UTION OF YEAES INTO
MONTHS, ACCOEDING TO SPECIAL RULES WHICH AEE
ADOPTED IN THE CALENDARS FOE CEETAIN DATES
OE  MOMENTS   OF  TIME.
 

Method of
ahargana, as
applied' to
special
dates.
 

Method of
the Khan-
dakhad-
yaka.
 

Not all the eras which in the calendars are resolved
into days have epochs falling at such moments of time
when just an adhimdsct or iXnardtrct happens to be com¬
plete. Therefore the authors of the calendars require
for the calculation of ctdhimdsa and ilnctrdtra certain
numbers which either must be added or subtracted if
the calculation is to proceed in good order. We shall
communicate to the reader whatever of these rules we
happened to learn by the study of their calendars or
astronomical handbooks.

First, we mention the rule of the Khanclakhddyaka,
because this calendar is the best known of all, and pre¬
ferred by the astronomers to all others.

Brahmagupta says : " Take the year of the Sctkctkdla,
subtract therefrom 587, multiply the remainder by 12,
and add to the product the complete months which have
elapsed of the year in question. Multiply the sum by
30, and add to the product the days which have elapsed
of the current month. The sum represents the partial
solar days.

" Write down this number in three different places.
Add 5 both to the middle and lower numbers, and
divide the lowest one by 14,945.    Subtract the quotient
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