NOTES 339 



rudiments of meteorology, there seemed to be no reason why air 

 inside the earth should not be affected by as violent hurricanes as 

 the air outside. And as such hurricanes were the most powerful 

 natural agencies known, their action was not unreasonably in- 

 voked to account for the phenomena of earthquakes. Assuming 

 that the air in a large subterranean cavern would behave as the free 

 open atmosphere does, the old philosophers did not find them- 

 selves under the necessity of explaining what was to set the air in 

 motion within the subterranean recesses and lash it into fury there, 

 any more than they had to account for tempests above ground. 



Obviously, if the air found its way from the outside into the 

 internal parts of the earth, it must have had equal facilities for 

 egress. And in the convulsions of an earthquake it might be 

 supposed to issue with violence through some of the previous 

 openings or from the rents made at the time. In corroboration 

 of the truth of the prevalent opinion, it was asserted that after an 

 earthquake air was found to issue from the ground, but no 

 account appears to have been preserved of any violent outrush 

 of air. As a further evidence that it is to the force of air that all 

 these internal disturbances are due, the author remarks that after 

 a violent earthquake another shock of equal violence cannot occur, 

 because the first has opened a passage for the struggling winds. 



The progress of investigation has, in modern times, thrown a 

 flood of light on the phenomena of earthquakes, though there 

 still remain many problems in the subject which await solution. 

 It is needless to say that no foundation whatever has been found 

 for the ancient faith that the air plays the chief part in these 

 subterranean commotions. 



Seneca discusses the nature of earthquake motion. He recog- 

 nises three kinds of movement quaking (succusszo), tilting (incli- 

 natio\ and trembling (vibratid) and he gives illustrations of the 

 kind of causes to which they may be referred (252). He believes 

 that the extent of country convulsed by an earthquake depends 

 upon the area of the subterranean cavern in which the wind 

 performs its exploits, and as these internal cavities do not con- 

 tinuously underlie vast tracts of the earth's surface, no large 

 spaces of that surface are simultaneously shaken. In his day 

 there appears to have been no record of a shock affecting the 

 whole basin of the Mediterranean Sea. He thinks that no earth- 

 quake ever extends as much as two hundred miles. He cites the 

 recent calamity in Campania, which did not pass beyond that 

 district, though marvellous tales about it had spread far and 

 near, and he gives other examples of the markedly local character 

 of the phenomena, so far as then known. He affirms that 

 maritime districts are those most frequently shaken (255, 257), 



