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ON SEISMOLOGICAL INVESTIGATIONS, 49 
the positions of foci of world-shaking earthquakes, not alone from the 
initial disturbanve, but also from ‘after shocks,’ which latter seldom reach 
distant places. 
When we know these foci, local observations enable us to make close 
approximation to the times at which large earthquakes have originated ; 
and when this is done our knowledge of the rates at which motion has 
been propagated in various directions through and round the world will 
become more reliable. 
The districts where such observations are required are indicated on the 
map, Plate IT. 
District E (Japan) is already well supplied with seismographs. Dis- 
tricts requiring similar installations are: A (Alaska), Band C (Central 
America and the West Indies), and K (Caucasian Himalayan district). 
In each of these at least six seismographs and the means of obtaining good 
time are needed. 
Other lines upon which geophysical and seismological research might 
be conducted, but which have hitherto received but small attention, are 
numerous. Our knowledge of earthquake movement as recorded under- 
ground as compared with that noted upon the surface requires extension. 
As far as we can learn from the excellent work inaugurated in the 
Adalbert Shaft at Pribram by Dr. Edmund V. Mojsisovics, it would 
appear that the movement, at a depth of 1,115 m., is for worid-shaking 
disturbances practically identical with that noted on the surface, from 
which it may be inferred that for this class of earthquake the large waves 
are not a mere superficial disturbance of the earth’s crust. 
Whether suboceanic disturbances are accompanied by molar displace- 
ments and large changes in suboceanic configuration remains to be 
determined by soundings the results of which should be of value to the 
hydrographer. 
The fact that at certain observatories unfelt teleseismic movements 
are accompanied by perturbations of magnetic needles, which disturbances 
remain without satisfactory explanation, suggests that if such irregular per- 
turbations are due to the influence of local subjacent magnetic magmas, 
in such localities not only should magnetic intensity be abnormal, but 
also that the differences between the observed and calculated values for 
gravity should be unusual. 
What are the relationships between seismic and volcanic activities ? 
and, further, what are the relationships between such phenomena, changes 
of level, magnetic elements, and the value for gravity ? are also questions 
the answers to which are at present largely based upon hypotheses. 
The movements on fault lines which accompany earthquake disturb- 
ances require an extended investigation, while the relationship which 
appears to exist between the dip and strike of rock folds and earthquake 
movement is a subject that has received but little attention. 
Much has already been done to establish a relationship between 
earthquake frequency and certain astronomical phenomena ; but fields for 
investigation, as, for example, the connection between movements of the 
earth’s crust and the wanderings of the pole, have yet to be exploited. 
Again, as bearing upon earthquake occurrence, secular movements of the 
earth’s crust, as, for example, those which are evidenced by changes in 
water level, alterations in the lengths of base lines and levels, the increase 
or decrease in the water-holding capacity of certain basins, have yet to be 
subjected to extended and careful measurements. 
1904. E 
