F 11
The days on which the ball failed to drop were:- April 14, (10h.), April 15, (16h.), April 16, (10h. and 11h.) and November 25, (10h.).
In the following table is given the number of times different errors occurred in the years 1920 and 1921:
Error. Number of Times, 1920 Number of Times, 1921 0'3 sec. or less 562 573 0'4 ** 61 0'5 34 21 0'6 15 21 1'0 1 2 0'9 1 0 1'1 ** ** 1 27 I J I J J1 173 " I 15 55 1.6 16 17 1.8 J 2.0 " 6 " ++~ + N N N N N - IThe mean probable error of the time ball in each month for the past five years is given in the following table:—
Probable Error of the Time Ball, 1917 1918 1919 1920 1921 Month. January, +0s.17 ±0s.24 +0s.17 ±0s.25 February, *10 13 *20 *30 13 March.. *11 15 '12 '21 ++ April. 18 *10 19 May, 15 '27 June, 17 '12 14 17 16 July, 10 14 13 17 21 August.. *11 13 '22 *10 September, '11 •26 15 11 10 October, 'IC 16 *24 *20 November, 10 '12 15 15 *10 December, '10 + '12 13 '11 Means,.. ±0s.13 ±0s.14 ±0s.15 +0s.18 +0s.18