F 16
Between January 1st and October 12th, the daily losing rate varied from -0s.86 to 0s.33, following generally the variations in pressure in the clock case. The clock stopped on October 12th, and various adjustments were made between October 13th and October 30th. It has been undisturbed since, the rate varying with pressure from +0s.55 to 0s.23. There has been no leakage into the clock case, the variations of pressure corresponding to those of temperature.
The Sidereal Clock, Dent 39741, was cleaned and the rate altered on February 4th; its rate was again altered on May 6th, May 9th, July 6th and August 28th, the tendency of previous years (a steady increase in losing rate), being particularly marked.
The Mean Time clock, Leroy 1350, was used for dropping the Time Ball, maintaining the electric time service in the Observatory, and sending hourly signals to the Railway, the Post Office, the Telephone Co., and the Eastern Extension Telegraph Co. The clock is corrected daily before 10 a.m. and before 4 p.m. by the electric regulating apparatus.
The daily rate of the pendulum is kept below 0.5 sec. by the addition or withdrawal of weights. Mean Time clock Dent, 39740, has been corrected daily and its rate regulated as in the case of Leroy 1350.
Chronometer Dent No. 40917 is on loan to Stonecutters Radio Station.
Batteries, Power Supply, &c.-The necessary current for the Time Service has been supplied by accumulator batteries, charged as found necessary from the alternating mains of the China Light and Power Co., Ltd., by the rotary converter or the Tungar rectifier.
IX. MISCELLANEOUS.
Seismograph. 210 earthquakes were recorded during the year by the Milne-Shaw Seismograph, as against 159 in 1925. The number for 1926 includes a series of 18 small earthquakes on August 5-6, 6 on August 7-8, and 4 on August 16. The seismograms have been forwarded to the President of the Seismological Committee, Oxford.
Upper Air Research.-35 flights with pilot balloons were made during the year, supplemented by 21 flights in seaplanes by Officers of H.M.S. Hermes and Vindictive, who observed the dry and wet bulb temperatures, usually at intervals of 500 feet up to 15,000 feet; or the maximum possible under prevailing conditions.
The results of the observations have been communicated to the Secretary of the International Committee for Upper Air