(b) The present practice of fixing watat by yet-lun pyo or yet-lon 27, 28 or 29, while it puts the Labyi of Second Wazo in Athanli in watat years, leaves the Labyi of Wazo short of Athanli in many common years,
(c) If the Athanli rule were fully observed it would immediately move the average Lent five days later than it is at present,
(d) If Lent is to be maintained permanently in, or even near, its proper place in the seasons, the solar year of the Surya Siddhanta must be abandoned, and the tropical year substituted for it.
114. Any calendar, if it is to have the maximum of practical utility and convenience, must be easily ascertainable for many years in advance. The best method hitherto devised to attain this end is to make use of cycles. The most notable example of this is the adjustment of days to years in the European calendar, which was first started by Julius Caesar, and afterwards improved by Pope Gregory XIII. The Julian cycle was 4 years, the Gregorian cycle is 4000 years. Every year which is a multiple of 4 is a leap year, except that every year which is a multiple of 100 but not of 400 is a common year, and 4000 and every multiple of 4000 is a common year. The Gregorian calendar is practically a perfect index of the seasons.
115. The Metonic cycle of 19 years is used by Christian churches to determine Lent and Easter, but the error of the cycle necessitates a complex system of adjustment of the golden numbers every century. Raja Mathan applied the Metonic cycle without any adjustment, and its error has produced in twelve centuries a marked divergence between the solar and average luni-solar years.
116. If reform of the Burmese calendar be undertaken, and the tropical year be adopted, the cycle method of regulating the calendar can be adopted, with practically no error, for there is one perfect luni-solar cycle, namely the cycle of 1040 years, which was discovered by the French astronomer de Cheseaux. 1040 tropical years equal 12863 lunations. This was absolutely correct without any error a few centuries ago. It is not so now because the length of the mean tropical year is decreasing at the rate of about one second in 200 years, while there is no appreciable change in the length of the mean lunation ; but the error is so small that it will not amount to one day in 10,000 years.
117. This fact may be easily verified. Three estimates of the length of the mean tropical year, according to modern science, are given in paragraph 106. If these three be multiplied by 1040, the results are respectively
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