EFFECT OF EXCHANGE OF ATMOSPHERES 225 



We have now passed in review some of the more salient dynamic fea- 

 tures of the greater earth. As pointed out at the start, the list can not 

 now be made complete. In time there will have to be added spheres of 

 influence springing from the electrical and magnetic properties of the 

 earth. There will also have to be added a great complex of more intimate 

 dynamic properties now more or less concealed within the body of the 

 earth, the dynamic properties which to a large extent make the earth body 

 what it is. All these, together with the outreaching influence gathered 

 about the material earth, make up the greater earth. 



Discussion" 



Professor Atwood : I would like to ask that Doctor Chamberlin speak 

 a little further on the exchange of atmospheres between the earth and 

 the sun. Is it likely to lead to enrichment or other notable change in our 

 atmosphere ? 



Professor Chamberlin : From my point of view, the interchange looks 

 rather toward uniformity, viewed in a large way, than to either enrich- 

 ment or depletion. Unless there is some radical change in the sun, there 

 should be no essential change in the equilibrium relations between the 

 ultra-atmospheres of the sun and those of the earth. Of course, there are 

 likely to be and have been minor variations. Some of these belong to the 

 very nature of the equilibrating process and some to. varying production 

 or consumption of atmospheric material by the earth. The preponder- 

 ance of logic, as well as geological and biological evidence, implies that 

 the earth's atmosphere has been in rather steady equilibrium with the 

 atmosphere of the sun. If the atmosphere of the earth, at any time or 

 for any cause, is depleted, the sun should throw more molecules of the 

 depleted sort into the atmosphere of the earth to restore the equilibrium; 

 and vice versa if the earth's atmosphere is overenriched. In the secular 

 action of this reciprocating process I find a satisfactory explanation of 

 that remarkable steadiness of the earth's atmosphere in mean composi- 

 tion and mean temperature which has characterized the ages, despite 

 some notable fluctuation, and which has made the continuity of the lead- 

 ing types of life a possibility. 



Question : Was there a vast difference between the results obtained by 

 you and Professor Moulton and those obtained by Sir George Darwin ? 



Professor Chamberlin: Not in so far as concerns the questions I 

 have been discussing. Doctor Lunn, taking Sir George Darwin's data, 

 found the dividing line between the two tidal spheres at 9,113 miles from 

 the center of the earth ; Doctor Moulton, using data of his own selection. 



