292
TABLE XI.—Continued.
Jan.
Feb.
Mar. Apr. May. June. July. Aug. Sept.
Nov. Dec. Year.
Number of days with
lunar corona,
2
1
Number of days with
lunar halo,
0
Number of days with
solar corona,
0
Number of days with
solar halo,.
0
Number of days with dew,
3
ta
Number of days with un-
usual visibility,
1
C)
2
Q
1
0
3
C)
2
6
N
O
6
1
6
5
3
3
6
7 11
3
3
3
4
Appendix B.
13
39
0
26
CI
30
63
33
Magnetic Observations made during the year 1898, Comparison of Magnetometers and Means of 15 years' Magnetic Observations made in Hongkong.
The observations of declination and horizontal force published in Tables XII, XIII, and XIV, were made with magnet No. 55 on Kew pattern unifilar magnetometer Elliott Brothers No. 55 (unless otherwise stated) and with magnets No. 83 and 83A on magnetometer No. 83. The dip observa- tions were made with dip-circle Dover No. 71, as usual.
The vibrations made with inertia bars published in Table XIV. furnish the moments of inertia by comparison with corresponding vibrations without the bars published in Table XIII.
The observations of horizontal force are expressed in C.G.S. units but the monthly synopsis in Table XV. exhibits also the vertical and total forces (computed by aid of the observed dips), and exhibits them also in British units and in Gauss's units. The value of log K for 25° Cent. was for magnet No. 55 3.44938±.00007 before cleaning, and 3.44901±0.00009 after cleaning, for No. 83 3.44851±0 00009, and for No. 83a. 3.46870±0.00004. The induction coefficient used was, for No. 55, 5.189±0.055, for No. 83, 5.151±0.084, and for No. 83A, 6.160±0.084. The temperature- reductions of m, the magnetic moments of the magnets, were as follows :-
No. 55 (Hongkong 1886): +0.000260t+ 0.00000244t2
No. 83 (Kew 1897): +0.000283t +0.00000102ť2
No. 83A. (Kew 1897):+0.000384t+ 0.00000166t
The times of vibration exhibited in Tables XIII. and XIV, are each derived from 12 observations of the time occupied by the magnet in making 100 vibrations, corrections having been applied for rate of chronometer and arc of vibration. The vibrations made with the inertia bar are usually the mean of vibrations made before and after vibrations taken without the bar.
The mean value of the magnetic moment of magnet No. 55 was 0.44794 in British units and 584.82 in C.G.S. units.