97

H.—34

APIA OBSERVATORY. The Apia Observatory has continued during 1929 its programme of observation in terrestrial magnetism, seismology, and meteorology. In July, 1928, the control of the Observatory was transferred from the Department of External Affairs to the Department of Scientific and Industrial Research. This change was brought about through the consolidation in one Administrative Department of all the various scientific activities of the country. The British Admiralty has contributed £400 and the Carnegie Institution of Washington £250 for the maintenance of the scientific programme. The New Zealand Reparation Estates has discontinued repairing the Observatory buildings, which has been a generous contribution of that Department made to this Observatory since 1921. The fundamental purpose for which the Observatory was established was to observe, measure, and record with the highest attainable accuracy the various physical elements affecting the earth and atmosphere at an isolated station in the South Pacific Ocean. During the year, although the staff was depleted, all essential records were secured and the founders' high purpose fully maintained. The visit in April of the non-magnetic research yacht " Carnegie " afforded an opportunity for the intercomparison of instruments and the discussion of observations and technique. During her second visit, in November, the " Carnegie " was totally destroyed by explosion and fire in the Apia Harbour. The death of Captain J. P. Ault and the destruction of this world-famed research ship was felt as a great personal loss. The various activities of the Observatory will be considered under the three divisions of terrestrial magnetism, seismology, and meteorology. Terrestrial Magnetism. Continuous photographic records were obtained throughout the year of the changes in the declination and horizontal force of the earth's magnetic field. Owing the failure of the earth's inductor, no observations of the inclination were obtained in January, February, and March. The behaviour of the variometer in April, May, and June was not satisfactory, and failed to give a record that could be used. Thus the values of vertical intensity are obtainable only from July to December. In order to compute the actual declination and horizontal force from the magnetograms the following absolute determinations of these elements were made at evenly spaced intervals : — Declination: 112 determinations on fifty-four different days. Horizontal force : 23. Inclination : 45, on forty-three days. The mean values of the magnetic elements —the so-called " all-days value " —for the past three years are given below : —•

Table I. —Magnetic Elements at Apia, 1927-29.

The days were classified according as the daily magnetic variation was normal, slightly or considerably disturbed. The individual daily character values were supplied quarterly to the Secretariat of the Comite International at De Bilt Observatory, Holland. Magnetic storms occurred on February 26-28, March 11-12, May 23, July 15, and September 22. Although the number of disturbed days was unusually high, the disturbances were not intense, but continued for a longer time than usual. The number of sun-spots observed in 1929 was above the average, which is closely related to the unusually disturbed magnetic state of the earth observed. The Observatory's magnetic standards were intercompared with those of the yacht " Carnegie." It was satisfactory to find that they had altered only very slightly since last compared in 1921. Seismology. The Observatory is equipped with 1,000 kgm. Wiechert seismograph for recording horizontal earth-movements, and a 180 kgm. Wiechert seismograph for recording vertical movements. From January 1 to February 9, and from June 9 to 24, the larger seismograph was out of action through the breakdown of its driving-clock. Except for those periods, a complete record was obtained from both instruments throughout the year. The two seismographs recorded a total of 269 earthquakes during the year, of which twenty-one were reported felt by people living in the vicinity of Apia. More than half (144) of the earthmovements recorded were exceedingly small tremors which originated within seventy-five miles of Apia. The amplitude of the earth-movement in the tremor rarely exceeded one five-hundredth of an inch, and the vibration continued less than five minutes. The larger earthquakes recorded were classified in Table II according to the distance of their epicentre from Apia.

1927. 1928. 1929. Declination .. j 10° 29-5' 10° 32-1' 10° 33-5' Horizontal force .. 35223 gammas 35225 gammas 35209 gammas. Vertical intensity.. .. , 20408 gammas (five months) 20418 gammas (six months).