AnnualReport-1921

F 10

VII, MAGNETIC OBSERVATIONS.

Magnetic observations were resumed in the new hut in October, the quarters on the site of the old hut having been completed in September.

In the following table the results of observations made with magnetometer Elliott 83 and dip circle Dover 71 in the new hut, for the epoch 1921.9, are compared with the values extrapolated from the observations made with Elliott 55 and Dover 71 in the old hut.

Observed in new hut with magnet 83 in unifilar 3 and dip circle 71. Extrapolated from observations in old hut with magnet 55.1 in unifilar 55 and dip circle 71. (b)-(a) (a) (b) Declination (west) 0.19.8 0.22.6 +2.8 Dip (north) 30.45.8 30:45:0 -0.8 Horizontal Force (C. G. S. unit) 0:37295 0:37190 -0.0105 Vertical Force (C. G. S. unit) 0·22199 0:22125 -0.0074 Total Force (C. G. S. unit)... 0.43402 0.43276 -0.0126

The quantities in the last column should therefore be applied to observations with Elliott 83 and Dover 71 in the new hut, to reduce them to the 1884-1920 series of observations.

VIII. TIME SERVICE.

Time Ball.- Prior to 1920, January 1, the Time Ball on Kowloon Signal Hill was dropped daily at 1 p.m. (120th Meridian Time). It is now dropped at 10 a.m. and 4 p.m. daily, except on Saturdays when it is dropped at 10 a.m. and 1 p.m., and on Sundays and Holidays when it is dropped at 10 a.m. only.

The Ball is hoisted half mast at the 55th minute and full mast at the 57th minute. If the ball fails to drop at the correct time it is lowered at 5 minutes past the hour and the ordinary routine repeated at the following hour, if possible.

When the Time Ball is out of order the above routine is carried out with flag "z", on the storm signal mast.

Time Signals are also given at night by means of three white lamps mounted vertically on the Observatory wireless mast. 8h. 56m. 0s. to 9h. 0m. 0s. p.m. the lamps are extinguished momentarily at the even seconds, except at the 2nd, 28th, 50th, 52nd, and 54th of each minute. The hours refer to Hongkong Standard Time (8 hours East of Greenwich).

The Ball was dropped successfully 657 times. There were 5 failures attributable to electrical or mechanical defects, and on three occasions the ball was not raised owing to the prevalence of high winds.