- F 14
losing rate (with superposed fluctuations corresponding to variations of pressure in the clock case due to temperature changes) until the end of October, since when the losing rate has shown a distinct tendency to decrease. No increase of pressure due to leakage in the case has been detected. The losing rate varied from -08.25 on February 12 to -0s.20 on October 5. Pressure in the clock case was reduced by about 15 m.m. on July 6.
The Leroy Mean Time Clock, No. 1850, 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 10h. and 16h. by the electric regulating apparatus. The daily rate of the pendulum is kept below 0s.8 by the addition or withdrawal of weights. The Dent Mean Time Clock, No. 39740, is held in readiness as a substitute for Leroy No. 1850. It was not required for this purpose in 1929.
IX. MISCELLANEOUS.
Seismograph.-No alterations were made to the seismograph during the year. New needle points were fitted as required. As against 183 in 1928, 252 earthquakes were recorded during the year 1929.
The seismograms have been forwarded to the President of the International Seismological Committee, Oxford, to be dealt with.
Upper Air Research.-82 balloon ascents were made during the year, 6 of which were observed with a second theodolite, 6469 feet to the north of the Observatory. 4 temperature flights were made by Officers of the R.A.F. from the Kai Tak base.
The result of the pilot balloon observations have been forwarded monthly to the Secretary of the International Commission for the exploration of the upper air.
The following days were selected by the International Commission as days for international ascents:-April 15-20, August 12-17, and December 17-19. December was chosen as the "International month". Balloon ascents were made on April 15-16. On the other International days the weather was too cloudy.
Rain-making Experiments.-The water shortage having become very serious, on June 18, R.A.F. planes from the R.A.F. base, Kai Tak, dropped 6 cwt. of powdered kaolin on cumulus cloud, with a view to producing rain.
The experiments were suggested by a Hong Kong resident and were sanctioned by the Naval authorities at the request of the Hong Kong Government, not with any hope of producing rain, but to satisfy the public. The result of the experiments was as anticipated.