LETTERS 



ON THE 



PHYSICS OF THE EARTH. 



LETTER I. 



GRAVITY, AND ITS EFFECTS. 



The ever-varying conditions of the earth and 

 of its surrounding atmosphere, the great changes, 

 which in the lapse of ages have passed over its 

 surface, and the mysterious forces, which are at 

 work within it, have occupied at all times the 

 thoughts of our race ; giving rise, as they do, to 

 numberless striking phenomena, and exerting a 

 direct influence upon our physical welfare. Hence 

 at all times thinking men have endeavoured to 

 obtain an insight into the laws which rule the Life 

 of our Planet. It is now no longer doubtful, that 

 the primaeval shocks and revolutions, through which 

 the earth has evidently passed, and to which it 

 owes its present form and state, were manifestations 

 of the same natural forces, whose action, sometimes 



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