INTRODUCTION. 3 



thermometer, the quantity of rainfall, and like phenomena 

 to which he devotes his attention. 



Next we may turn to the more practical aims of seis- 

 mology and ask ourselves what are the effects of earth- 

 quakes upon buildings, and how, in earthquake-shaken 

 countries, the buildings are to be made to withstand them. 

 Here we are face to face with problems which demand 

 the attention of engineers and builders. To attain what 

 we desire, observation, common sense, and subtle reason- 

 ing must be brought to bear upon this subject. 



In the investigation of the principle on which earth- 

 quake instruments make their records, in the analysis of 

 the results they give, in problems connected with astro- 

 nomy, with physics, and with construction, seismology 

 offers to the mathematician new fields for investiga- 

 tion. 



A study of the effects which earthquakes produce on 

 the lower animals will not fail to interest the student of 

 natural history. 



A study like seismology, which leads us to a more 

 complete knowledge of earth-heat and its workings, is to 

 be regarded as one of the corner-stones of geology. The 

 science of seismology invites the co-operation of workers 

 and thinkers in almost every department of natural 

 science. 



We have already referred to the influence exerted by 

 earthquakes over the human mind. How to predict 

 earthquakes, and how to escape from their dangers, are 

 problems which, if they can be solved, are of extreme 

 interest to the world at large. 



In addition to the sudden and violent movements 

 which we call earthquakes, the seismologist has to in- 

 vestigate the smaller motions which we call earth-tremors. 

 From observations which have been made of late years, 



