Appendix F.
REPORT OF THE DIRECTOR OF THE ROYAL OBSERVATORY, HONGKONG, FOR THE YEAR 1923.
1.--GROUNDS AND BUILDINGS.
The grounds were kept in order by the Botanical and Forestry Department with the assistance of the Observatory coolies.
In October two rows of iron shelves were fixed round the wall of the Old Time-Ball Tower to take the overflow of records from the Observatory.
The underground room for the seismograph and clocks was completed in the month of May. It consists of a double room with an air space of 2 feet between the inner and outer walls and roofs. The floor is 17 feet below the level of the ground. The inner room is 20 feet square and 10 feet 9 inches high at centre, with 9 inch brick walls.
The outer walls are of concrete, 2 feet 6 inches thick at the base tapering to 12 inches thick at the top.
Both roofs are of ferro-concrete. The outer roof is 4 feet below the level of the ground and is covered with disintegrated granite, which is turfed to the level of the surrounding lawn.
In the middle of the room is the seismograph pillar, a block of concrete 6 feet by 4 feet rising from a depth of 10 feet below the floor. The latter consists of 6 inches of lime and red earth concrete covered with 4 inches of cement concrete. It is not in contact with the pillar. The corners of the inner walls are bricked in so as to make the horizontal section an isosceles right-angled triangle, of which the hypotenuse is 4 feet. These will serve as pillars for the clocks.
A system of subsoil drainage is provided and ventilation is assisted by a 9 inch extract pipe, running to the roof of the Observatory, which connects with the air space between the inner and outer roofs. 18 inch cast iron grids are also provided at ceiling and floor levels to give air communication between the chamber and enclosing air space.
Steps leading from the verandah in front of the old Clock Room give access to the inner room through two pairs of swing doors four feet apart.
The room was very damp at first, the mean relative humidity in May being 96%. At the end of June five radiators were installed temporarily, and with the current on for 48 hours the relative humidity was reduced from 96% to 75%. On removing the