286 ' EAKTHQUAKES. 



sucli a view, insomuch as they occur more often at the 

 syzygies, or epoch of the spring tides, than at neap tides — 

 an observation found in the works of Georges Baglivi 

 (1703) and Joseph Toaldo (I770).i 



Prof. Perrey, of Dijon, who did so much for seismology, 

 held the view that the preponderance in the number of 

 earthquakes felt at particular seasons was possibly due to 

 the attractive influence of the sun and moon producing 

 a tide in the fluid interior of the earth, which, acting on 

 the solid crust, produced fractures. 



Rudolf Falb, whose writings have of late years 

 attracted considerable attention, brings forward views 

 which may be regarded as amplifications of those sug- 

 gested by Perrey. 



According to Falb, the inner portion of the earth 

 must be regarded as fluid. In the crust above this fluid 

 reservoir are cracks and channels, into which, by the 

 attraction of the moon and sun, the fluid is drawn. On 

 entering these cracks cooling takes place, together with 

 explosions of gas and subterranean volcanic disturbances. 

 The attractions producing the internal tides required by 

 Falb are chiefly dependent upon the following factors : — 



1. The nearness and distance of the sun from the 

 earth (January 1 and July 1). 



2. The position of the moon with regard to the earth, 

 which in every twenty-seven days is once near and once 

 distant. 



3. The phases of the moon — whether full or new 

 moon (syzygies), or whether first or last quarter (quad- 

 ratures). 



4. The equinoxes, the position of the sun in the 

 equator, and the relative position of the earth. 



5. The position of the moon relative to the equator. 



* Comjytes Rendns, August 1854. 



