F 12
The Time Ball was dropped successfully 664 times. There was one failure, on December 16th at 10 a.m., owing to an injury sustained by the coolie, when hoisting the ball. It was dropped successfully at 11 h. The ball was not raised on June 26th at 10 h a.m, owing to high wind, and on July 14th at 4 p.m., during a severe thunderstorm.
In the following table is given the number of times different errors occurred in the year 1924 and 1925.
Number of Times. Error of Time Ball. 1924 1925 03 sec. or less 530 631 0'4 " 44 12 0'5 37 8 0-6 "> 23 5 0'7 10 3 "J 0.8 5 0'9 27Errors of 1.2, 1.9 and 2.0 seconds respectively occurred on one occasion. All errors in excess of 0.7 second occurred during the period January 16 to 22 when the rates of the sidereal clocks were seriously disturbed by workmen. No error greater than 0.4 has occurred since March 27th.
The mean probable error of the time ball in each month for the past five years is given in the following table:
Month. 1921 1922 1923 1924 1925 January, +0.25 ±0.10 ±0.16 ±0.26 ±0.38 February, *22 March... *12 *22 April. '20 *18 *16 May, *16 *10 'I I June, *17 *I I *10 July, *IO *Iz *2 I August, *10 *10 *28 *16 September, *20 *15 '10 October, '10 *18 November, *IO December, 'I I *10 '21 •14 Means, +0.18 ±0.13 ±0.17 ±0.19 ±0.15