212 ■ T. C. CITAMBERLIN THE GREATER EARTH 



Like the broad "turn-rows" lietween tlie pioneer farms — with which we 

 of the older school were once so familiar — its cultivation has been left for 

 a later day. It is still largely virgin soil. 



It has therefore seemed worth while to assemble in diagrammatic form 

 some of the more salient features of the dynamic earth. In this I am 

 little more than a compiler. I shall do little more than put together 

 what I have picked up here and there during the last tAventy-five years 

 and found useful in the study of earth problems. The compilation may 

 serve your convenience, for the items were found scattered through a 

 wide range of literature relating to several dilferent subjects ; some, in- 

 deed, have not been given a definite literary form at all.. These I have 

 drawn out from those who happened to have them, or happened to have 

 the unrelated material from which they might be organized. 



It is too familiar to need saying that tlie gravity of the earth reaches 

 out far beyond its material organization and brings to bear a certain 

 measure of distant influence ; it is not so clearly recognized that this rises 

 to certain specific degrees of dominance over definite portions of the space 

 around the earth and falls to a merely negligible degree of influence over 

 the space beyond that. Only the controlling influences interest us as 

 students of the earth ; but these are vital. I shall deal with little beside 

 the gravity prowess of the earth, starting with the earth's gravitative 

 sphere of control. The earth is enveloped by spheres of electrical and 

 magnetic influence, but the present state of our knowledge does not war- 

 rant an effort to define these. And then there are many intimate forces — 

 crystalline, colloidal, chemical, cohesive, adhesive, etcetera — which deter- 

 mine the more immediate structures of the earth-body. Of these I shall 

 not speak ; I merely wish here to recognize that they are essential in a 

 complete picture of the dynamic earth. The gravitative influence of the 

 earth must stand as its dynamic representative ; this is not unfitting, 

 since it appears to be the most important of the outreaching forces. 



The Eai^tii's Sphere of gravitative Control 



Many years ago Laplace recognized that the earth and similar bodies 

 had special spheres of gravitative influence, and the phrase "spheres of 

 influence" came into use among astronomers as the technical term for 

 this, so far as the subject received attention at all. The phrase is em- 

 ployed in a sense closely like that in use in international affairs ; it does 

 not so much designate the form as the degree of influence. The "sphere 

 of influence" of Japan in C^hina is not spherical, nor does the "sphere of 

 influence" of a planet imply that it is spherical, though it is usually 

 spheroidal. 



