2 . EAKTHQUAKES. 



to US, have exerted an influence upon the imagination 

 and understanding ; and just as a sudden fright may 

 affect the nerves of a child for the remainder of its life, 

 we have in the annals of seismology records -which indi- 

 cate that earthquakes have not been without a serious 

 influence upon the mental condition of whole communi- 

 ties. 



To a geologist there are perhaps no phenomena in 

 nature more interesting than earthquakes, the study of 

 which is called Seismology. Coming, as shocks often will, 

 from a region of volcanoes, the study of these disturbances 

 may enable us to understand something about the nature 

 and working of a volcano. As an earthquake-wave travels 

 along from strata to strata, if we study its reflections and 

 changing velocity in transit, we may often be led to the 

 discovery of certain rocky structures buried deep beneath 

 our view, about which, without the help of such waves, it 

 would be hopeless ever to attain any knowledge. 



By studying the propagation of earthquake- waves the 

 physicist is enabled to confirm his speculations respecting 

 the transmission of disturbances in elastic media. For 

 the physicist earthquakes are gigantic experiments which 

 tell him the elastic moduli of rocks as they exist in 

 nature, and when properly interpreted may lead him to 

 the proper comprehension of many ill-understood pheno- 

 mena. It is not impossible that seismological investiga- 

 tion may teach us something about the earth's magnetism, 

 and the connection between earthquakes and the ' earth 

 currents' which appear in our telegraph wires. These 

 and numerous other kindred problems fall within the 

 domain of the physicist. 



It is of interest to the meteorologist to know the con- 

 nections which probably exist between earthquakes and 

 the fluctuations of the barometer, the changes of the 



