160 The N.Z. Journal of Science and Technology. [Sept. 
activity, and also with regard to the amplitudes and origins of the diurnal 
and annual periodic variations of the magnetic elements. 
(2.) Seismic Observations .—-The observatory is equipped with—(a) a Wie- 
chert astatic inverted pendulum for two horizontal components (north and 
east); (b) a Wiechert vertical component seismograph (these record on smoked 
paper); (c) a horizontal pendulum for tilt, with photographic recording. 
Besides the excellent seismograph records which these instruments give, 
from which the distances and peculiarities of earthquakes can be deduced,* 
the initial impulses on the north and east components on a Wiechert seis¬ 
mogram are particularly suitable for the determination of the azimuth 
from which an earthquake wave arrives at the observatory. 
Fig. 3.—The Samoan Observatory. 
Apia is in a particularly useful position for investigating the nature 
and progress of the disturbances arising from the earthquake-line stretching 
from New Zealand north-eastwards through the Tonga deep. Of further 
scientific interest is the recording of the disturbances originating in the 
neighbouring volcanic island of Savaii, and also of the interesting movements 
of the ocean-bed in the Pacific. The records have also proved valuable in 
the determination of earthquake centres in the south-west Pacific. These 
results are important also from the point of view of their influence on the 
best routes for submarine cables. 
Besides these particular cases it may be said that Samoa is one of the 
most important seismological and magnetic stations in the world, as it forms 
a necessary link in the chain of such stations from New Zealand and 
Australia, Batavia, Manila, China, and Japan to Honolulu and America. 
* See G. Hogben, The Interpretation of a Typical Seismogram, this Journal, vol. 3, 
pp. 106-110, 1920. 
