19. More on the same subject: for those who do not know how to calculate
TRANSLATION
when twenty-four days old by a space of nine months and eighteen days; when twenty-¢ve days old by a space of ten months; when twenty-six days old by a space of ten months and twelve days; when twenty-seven days old /343/ by a space of ten months and twenty-four days; when twenty-eight days old by a space of eleven months and six days; when twenty-nine days old by a space of eleven months and eighteen days; when thirty days old by a space of twelve months.
19. MORE ON THE SAME SUBJECT: FOR THOSE WHO
DO NOT KNOW HOW TO CALCULATE
Should someone rather less skilled in calculation nonetheless be curious about the course of the Moon, we have also for his sake devised a formula [argumentum] adapted to the capacity of his intelligence, so that he might ¢nd what he seeks. Thus we have marked out each day of the twelve-month annual circuit [in the calendar]195 by means of alphabets, so that the ¢rst and second [alphabetical] sequences each comprise twenty-seven days, while the third [sequence] has one [day] more, namely [the day] which accrues from three repetitions of the eight super- £uous hours. In order that there might be enough letters for the days we wish to indicate, we have not placed them against every day, /344/ but against every other day. Hence it is not necessary to take the alphabet beyond the letter O.
At the beginning of the present work, we have included the Table of Regulars [Pagina regularum], which contains nineteen alphabets like those described above, each beginning with a di¡erent letter, for all the years of the 19-year cycle, together with the twelve names of each of the months and signs, arranged in this sequence according to the number of days in which the Moon traverses the zodiac. Along its length, the table has twenty-seven rows, with the names of the signs noted on the left and the names of the months on the right, so that someone unfamiliar with the signs can ¢nd what he wants by noting the months. Across its width it has nineteen columns; the order of the 19-year cycle is shown by the number of years noted at the top.
So if you wish to know what sign or what part of the month the Moon is in on any given day of any year, open the [calendar-]codex, and note the letter pre¢xed to that day. Then, turning to the Table of Regulars in 195 See Appendix 1.