12 SCIENCE PROGRESS 



developed within the Earth by the mutual gravitation of its 

 parts, it becomes less surprising. A similar value was inferred 

 by combining the result of horizontal pendulum experiments 

 with the result of observations concerning variation of latitude. 

 The value required in the crust is about the average rigidity 

 of many kinds of granite and marble. The result that, for the 

 proper transmission of the initial phase of the large waves, 

 the rigidity should increase beneath the crust, points to a 

 gradual transition from the mechanical properties of the crust 

 to those of the nucleus, a thing probable enough. The general 

 result that the Earth as a whole is a very rigid body, not 

 a fluid body coated over with a thin solid crust, is so well 

 supported by the observations of the fortnightly tide, by the 

 experiments with horizontal pendulums, by the period of the 

 variation of latitude and by the interpretation of seismic records, 

 that it should by now be regarded as firmly established. 



