F 11
The ball was not raised on November 5, owing to strong wind. It fell with an error of 0’3 or less on 300 occasions, with an error of 0’4 or 0’5 on 37 occasions, and 0’6 or 0’7 on 14 occasions. Errors of 0’8 occurred four times, of 0’9 once, of 1’0 four times, and 1’1, 1’2, 1’3, 1’8, and 2’3 once each. The probable error varied from 0’10 in October, to 0’43 in February.
Portions of the framework and cover of the ball were repaired in the month of May.
Transit Instrument.—Observations for time were made daily with the 3-inch transit instrument and the Hipp tape chronograph by the Chinese computers, weather permitting.
The number of observations in the years 1914 and 1915 were as follows:-
1914 1915 Transits, 1,803 1,817 Level determinations, 893 $54 Azimuth determinations, 47 32 Collimation determinations, 43 30Transits of the sun were only observed when star transits were not available from the previous night.
The azimuth and collimation determinations were made by the Chief or First Assistant. The azimuth determinations depend usually on observations of the north and south marks.
The ruled glass scale, which was substituted for the spider threads in the transit instrument on 1914 August 18, was replaced by a new glass with deeper lines in April 29. The lines on the original glass were too fine, and invisible in certain lights.
Clocks. On March 29, the Standard sidereal clock, Dent No. 39,741, was cleaned and fitted with an invar pendulum, and hardened lead bob. The pendulum was regulated to a losing rate of 0’2 a day, but the rate increased to 1’2. It was again regulated on June 1 and 3, after which its rate varied from +0’30 on June 9 to +0’08 on June 30. It then remained remarkably steady till July 26. From this date its rate commenced to decrease, reaching -1’04 on October 12, when it was again regulated. After a very steady period the rate increased from +0’02 on November 11 to +0’36 on November 19. It has fluctuated between +0’33 and -0’08 since.
At present there is not sufficient data available for determining the temperature, pressure, and humidity co-efficients. When examined at the National Physical Laboratory, London, the mean co-efficient of linear dilatation of the pendulum rod was found to be 0’0000017 between the temperatures 32° and 86° Fahrenheit.
It is suspected that the electric sidereal clock on the same pillar, which was re-started on November 17, has affected the rate of the sidereal standard. If an appreciable effect is found new pillars will have to be provided for the electric sidereal clock, and also for the Brock mean time clock which is on the same pillar as the Dent mean time clock.
In the following table is given the excess of the observed over the calculated rate after cloudy periods in the year 1915 :--