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Appendix A.
Magnetic Obserrations made during the year 1899, and Comparison of Magnetometers.
The observations of declination and horizontal force published in Tables XI and XII were made with inagnet No. 55 on Kew pattern unifilar magnetometer Elliott Brothers No. 55 and with magnets 83 and 83A on magnetometer No. 83. The dips were observed with dip-circle Dover No.
71.
The times of vibration are cach derived from 12 observations of the time occupied by the magnet in making 100 vibrations, corrections having been applied for rate of chronometer and are of vibration. The value of log K for 25° Cent. (determine in 1898) was for No. 55 3.44901±0.00009, for No. 83 3.44851±0.00009, and for No. 53a 3.46870±0.00:04. The induction-coefficient is for No. 55 5.189±0.055, for No. 83 5.151±0.084, and for No. 83A 6.160+0.084. The temperature-coefficients of the magnetic moments are as follows :--
No. 550.000260t+ 0.00000244t' (Hongkong 1886)
No. 83: +0.000283t + 0.00000102ť (Kew 1897)
No. 83A: +0.000384t+0.02000166t (Kew 1897)
The mean value of the magnetic moments were for No. 55 581.51, for No. 83 762.06, and for No. 83A 676.34.
The horizontal forces in Table XIII observed with No. 83 have been corrected by the subtraction of .00064, and those with No. 83a by subtraction of .00037 in order to reduce them to No. 55. The uncorrected means of observed values of horizontal force were for No. 55 0.36676, for No. 83 0.36740, and for No. 83A 0.36713.
T
All forces are expressed in C.G.S. units. The vertical (Y) and total forces exhibited in Table XIII have been obtained from the observed dips. The mean values of the dip obtained with needle No. 3 was 31°29'.08, with No. 4 31°29′.55, with No. 7 31°28′.63, aud with No. 8 31°30'.19. No corrections have been applied to the dips observed with the different needles.
In September the horizontal force was determined with Collimator magnet 55 used in magneto- meters 55 and 83 alternately. The result obtained in the latter exceeded the value obtained in the former by 0.00040, which agrees with the value by which the mean of the two horizontal forces obtained by the magnets 83 and 83A in magnetometer 83 exceed that obtained with 55 (0.00052 in 1898 and 0.00051 in 1899). The values of m x obtained from vibrations
igree. The values of do not agree. The cause lies with the deflection bars. The bar belonging to 55 is certified to be correct throughout. The apparent distance from centre of instrument of graduation on bar belonging to 83 marked 30 cins is 29.990, and that marked 40 cmns is 39.990 according to the certificate, and those corrections have been applied here. But when the two deflection bars are placed beside each other it is seen by the naked eye that these corrections are wrong. It is presumed that the bar belonging to 55 is right. It may be suspected that all the disagreements that are found between the results obtained with different magnetometers are caused by defective determination of the constants of the
instruments.