# VII.-MAGNETIC OBSERVATIONS.
Magnetic horizontal force, declination, and dip are observed at the observatory once a month. In the dip observations 4 needles are used in rotation, the result for each month being the mean of determinations with two needles.
In the following table are given the annual values of the magnetic elements in 1927, as derived from observations made in the magnetic hut with magnetometer Elliott 83 and dip circle Dover 71:
Declination (West) 0°31.7' Dip (North) 30°39.9' Horizontal Force (C.G.S. unit) 0.37376 Vertical Force (C.G.S. unit) 0.22161 Total Force (C.G.S. unit) 0.43452Monthly determinations of horizontal force and declination have been made at the new Magnetic Station, Au Tau, simultaneously with those at the Royal Observatory from March to December inclusive, the new Magnetometer (Cooke Troughton and Simms No. 31) being utilised for the purpose.
The results (mean for 10 months) are:
Declination (West) 0°44.4' Horizontal Force (C.G.S. unit) 0.37433No observations of dip were made as the inductor received in 1926 had to be returned for repair. It was not received back until late in the year and several difficulties had to be overcome before the instrument could be brought into regular use.
A comparison of the two magnetometers was made at the Royal Observatory during January and February, and indicates that a correction of γ9 is necessary to reduce the horizontal force results by the Cooke instrument to those of Elliott No. 83. No appreciable difference was found in declination determinations.