Page:Results of meteorological observations, 1894.djvu/13

 Astronomical Department.

To ascertain the error and the rate of change of the sidereal clock, the transits of fixed s f ars have been ob- served as usual with the transit instrument, the adjust- ment of which to the meridian line was frequently tested by the late Mr. A. Y. Nursingrow.

The time gun is fired every evening at 9 P.M. mean time. The exact time is given every morning by means of signals on the flagstaff on the Dolphin's Nose by the following arrangements :

1st. The flag B with the flag C below it is hoisted on the flagstaff precisely at 8 o'clock (weather permitting) every morning.

2nd. The error in the mean time of the flash of the previous evening's gun is exhibited on the yard-arm by means of the flags 1, 2, 3, &c. y to the nearest tenth of a minute.

3rd. When the flags indicating the error of the gun are hoisted on the eastern extremity of the yard-arm it is understood that the gun was fired too early, and the contrary when they are hoisted on the western extremity.

4th. The flag A is hoisted below another flag to indi- cate that the number of tenths of a minute is the same as the number of minutes. This is done to avoid using duplicates of the flags.

5th. The flags hoisted on the yard-arm indicate minutes and tenths of a minute corresponding to their numbers. The numbers of the upper flags denote minutes and those of the lower ones, tenths of minute. When the error does not amount to a whole minute, a single flag is hoisted a little below the extremity of the yard-arm to indicate the error in tenths of a minute. For example, the number of the upper flag on the yard-arm being 2, denotes 2 minutes ; and that of the lower one being 3, denotes 3 tenths of a minute ; and if they are on the eastern extremity, the signals signify that the gun was fired 2*3 minutes in advance of the exact mean time.

6th. The flags B, C and are hoisted on the mast- head when the gun has been fired correctly.

7th. The signals continue to fly from 8 to 9 o'clock in the morning when they are hauled down.

The time gun is sometimes not well heard during the