THE BOWELS OF THE EARTH. 



39 



would yield to the attraction of the sun and moon as the oceans 

 now do. Some effects of this pull may indeed be seen in the distri- 

 bution of earthquakes, which are more frequent at full moon than 

 at other times, as though the strain produced by the attraction of 

 the moon helped to produce these shocks by the cracking and giv- 

 ing way of the earth. But if the earth as a whole were anything 

 like as fluid as water, it would yield as a whole and assume the 

 same shape, bulging about as much toward the moon as the wa- 

 tery envelope, so that the water would not be perceptibly deeper 

 toward the moon than elsewhere ; whereas, if it were perfectly 

 rigid, it would retain its shape unaltered, and the water about it 

 alone would be drawn by the moon. It would be pulled up into 

 tidal waves. These two different cases and effects are illustrated 

 in Fig. 1. As a matter of fact, we find that the heights of the 

 tides are nearly as great as though the earth were absolutely rigid. 

 The earth, therefore, must be exceedingly rigid ; we may say solid, 

 so far as these tidal strains are concerned. These are, however, 



A E B 



Fig. 2. P, point of origin of earthquake shock; E (epicentrum), point on the surface directly 

 over it ; A, B, limits of the area of vertical, .simultaneous, and earliest shock. 



so varying in their application, shifting their direction through 

 all the points of the compass every twenty-four hours, that if the 

 interior of the earth is very viscous and we know that hot iron 

 is in just this viscous condition when at welding heat the yield- 

 ing to forces so rapidly changing direction might be no greater 

 than that which is observed. 



Another argument for the solidity of the earth is based on the 



