13614. (C. L. Dodgson, M.A.)—Zeller’s formula for the day of the week corresponding to any given date, viz., the pth day of the qth month of the year N, New Style, is where means the integral number of 4’s contained in N. Taking a hint from this, I have succeeded in evolving an algebraical formula for the number of days in the qth month. I take a certain algebraical function of q, and divide it by 5, and call the remainder r. Then a certain algebraical function of r will give the number of days in the qth month. This works correctly for March and all following months; and even for January, by calling it the 13th month of the proceding year; but I cannot manage February.