ASTRONOMY AT THE FRONT: A LUNAR CALENDAR IN THE MEMORY.
[TO TOR EDITOR OF THE " SFECTATOR.") Sra,—Your correspondent Mr. W. J. Bremner Davis gives a rule, not very exact but quite useful, for tolling the ago of tho moon on any day, in any year, if you know the date of the new moon in March of that year. I have during many years peat supplied my friends with an old well-known rule which does not require that knowledge. When the rule has been learnt it is surprising how often one finds occasion to use it, oven when Zeppelin raids and night battles are not in the mind. To find the age of the moon on any day in any month in any year. There aro a day number, a month number, and a year number, easily remem- bered. You add these together and whenever the number exceeds 30 you subtract 30. The result is the ago of the moon on the day specified. 0 or 30 signifies now moon, 15 full moon, 7k and 22k the quarters.
(1) The day number is the day of the month.
(2) The month number is easily remembered if you write down the 12 initials of the months and read the corresponding numbers, in pairs, thus :— JF MA MJ JA SO ND 02; 02; 24; 46; 78; 910.
This is the only real feat of memory required.
(3) Tho year number for any year is got by subtracting 1911 from the year, and multiplying by 11 (subtracting 30 if necessary). The year number for 1911 is 0, and to this we add 11 each year. This acci- dental coincidence of the numbers 11 and 1911 is a groat help to the memory. Take the date 1916, October 18th.
The day number is ..
The month number is ..
The year number (11 x 5 — 30) is And the ago of the moon is 21 days, got by subtracting 30. The answer is very seldom one day in error.—I am, Sir, &c.,
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18 8 25 51
Kinnaird Cottage, Pitlochrie. GEORGE FORBES.
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