56o 
GEOPHYSICS: H. F. REID 
Proc. N. a. S. 
factory recording of earthquakes. The origin of these vibrations is not 
understood. They may be connected with meteorological conditions. 
The actual movements of the ground, velocity and direction of propaga- 
tion of the microseisms should all be studied and compared with the direc- 
tion of the wind and the direction of the barometric gradient. The con- 
centration of a number of similar seismographs in a limited area would 
furnish the proper conditions for the solution of this problem. 
The influence of the foundation, rock or alluvium, upon the intensity 
of the vibrations; the relative intensity of the movement in a mine and 
above ground, due to local or to distant earthquakes, etc., are examples 
of regional problems before us. 
The study of the actual effects of strong earthquakes usually follows 
somewhat different methods. It requires the examination of the region 
where the shock has left visible marks by a competent seismologist. The 
experiences of persons present must be collected; the damage to buildings 
and other structures noted; and the relation of the earthquake to the 
geology of the region determined. The slow surface waves in alluvium, 
sometimes called "gravity" waves, are still a great enigma, and require 
special attention. A few portable seismographs should be available 
and should be placed in suitable positions to record and locate the after- 
shocks. If in addition to these field studies, instrumental records before, 
during, and after the strong shock should have been made the two kinds 
of information collected would not only supplement but would add greatly 
to the value of each other. 
C. Theoretical and Auxiliary Problems 
The results obtained by world-wide and by regional studies must be 
woven together into a unified whole and the fundamental laws of the 
sciences deduced. This kind of work is only done occasionally, and then 
by individuals who have developed an unusual insight into their science. 
There are many problems, however, which do not come either under the 
world-wide or the regional problems, which are important either in helping 
the solution of these problems, or in elucidating the meaning of the data 
collected. For instance, the theoretical and experimental study of seismo- 
graphs is of great importance. It looks to a better interpretation of the 
seismograms, and to improvements of the instruments, or the develop- 
ment of new forms of instruments. This is work to be done in the study 
or in the laboratory, but should be in close touch with observations in 
the field. In particular, we need an instrument that will give a correct 
record in the shaken area of a strong earthquake. 
Then there are many problems, such as the actual genesis of the vibra- 
tions, the transmission of body and surface waves, the changes in the 
character of the waves on reflection, the reasons for differences in the in- 
strumental records of different earthquakes, the peculiarities of earth- 
quake sea-waves, etc. 
