MODERlSr SEISMOLOGY SCRASE 203 



to the conclusion that there is no good evidence that waves on one 

 coast or another are directly responsible for the production of 

 microseisms. Neither is there any satisfactory evidence that the 

 phenomenon is due to sea waves in shallow water. There still 

 remains the possibility that sea waves in deep water are effective, 

 but this idea involves certain theoretical difficulties which must be 

 cleared up before a satisfactory explanation is obtained. The effect 

 of geological structure on microseismic disturbance has also been 

 inA'estigated theoretically by Lee, and it appears that the larger 

 microseisms are to be expected where the sedimentary rocks are of 

 greater thickness; the results of the world survey show that this 

 conclusion is consistent with the geological evidence. 



CONCLUSION 



It will be realized from this brief outline that modern seismology 

 affords an excellent illustration of the progress which can be made 

 by the application of sound physical principles to a subject which 

 hitherto had no claim to be recognized as a science. From the 

 foundations so firmly laid by Milne seismology has developed in 

 accordance with the requirements of modern investigation and has 

 become a quantitative science well worthy of its place as a branch 

 of geophysics. It has already thrown much new light on the 

 properties and structure of our globe, and it provides the most 

 hopeful means of probing the secrets of the earth's interior. 



