19 - 6 = 13. From 13 take 7, and 6 remains—that is, the 19th of August falls on a Saturday.
If the date of the day wanted be smaller than that indicated by the final consonant of the suggestive name of the month, add 7 before commencing, instead of subtracting it afterwards. April 1st falls on a Saturday. April, suggestive name Apron ( n = 2 ). You cannot subtract 2 from 1. Add 7 first; 7 + 1 = 8; from which take 2, and 6 will remain. The 6th day is Saturday. Again, November 3. Nova (5). Add 7; 7 + 3 = 10. 5 from 10 = 5—Friday.
Why this is the case, will be seen from the consideration of the fact that, when the number indicated by the last consonant of the suggestive name of the month is subtracted, the remainder is a certain number of days beginning with a Monday; from which, if you take as many seven days (complete weeks) as you can, the remainder, if any, must be so many days after Sunday.
In the case of the year 1864, for obvious reasons, 1 must be subtracted before commencing, for any date up to February 29th. After that day, subtract 2. 1863, subtract 3 before commencing, and proceed as above. 1862, subtract 4. 1861, subtract 5. For 1866, add 1 before commencing; 1867, add 2; 1868, add 3 up to 29th February: after that date add 4. And so on. Of course the above calculations depend entirely upon the fact that the year 1865 is taken as the starting point. In the case of any other year being taken, the mode of procedure must naturally be different.
