646 EEPORT— 1897. 



sbrinkage of the earth gradually, owing to its owe gravity, would give a sufficient 

 amount of contraction to explain not only the phenomena of mountains and archjean 

 crumplings, but of plateaux, continents, and ocean basins. Computation shows that 

 the internal heat generated by the time the eai-tb reached its maturity would be 

 ample to explain the present internal heat, and account for much loss during 

 geological ages. 



This is a departure from the common view of the history of the atmosphere in 

 supposing it to be<rin as a tenuous envelope, and be subject both to enrichment and 

 depletion during all its subsequent history. The supply from within is very imper- 

 fectly known. The air and ocean together are only about one-fiftieth of 1 percent, 

 of the earth's mass. The increase of the atmosphere from without is almost wholly 

 a matter ot conjecture'. 



The emanations from within would doubtless be more abundant at times of 

 igneous extravasation and of the disruption of the crust than at other times, so 

 that the supplies to the atmosphere would vary according as the average of the.=e 

 conditions varied. The impoverishment of the atmosphere, particularly in respect 

 to its carbonic acid, was probably dependent very largely upon topographic states. 

 When the land was elevated the underground water-level was relatively deep beneath 

 the surface, and the penetration of aerated waters below was also deep, and the 

 alteration of the rocks went on relatively rapidly. "When the land was depressed 

 or cut down to an approximate base-level the underground water surface was 

 shallow, and the penetration of aerated waters below that was also shallow, and 

 the change of the rocks was slow. Whenever, therefore, the land on an average 

 stood high, the impoverishment of the atmosphere went on rapidly ; whenever it 

 was low, slowly. Combining this with the irregularities of supply, it appears 

 that enrichment and impoverishment would generally run together and give, on 

 the whole, a somewhat uniform atmosphere ; but in the nature of the case the two 

 were not strict;ly concurrent, and as a result at times there was enrichment, and at 

 times depletion of the atmosphere. From these it is held that great climatic 

 changes would arise. Scantiness of carbonic acid would be correlated with cold 

 temperatures, as maintained by Tyndall aud others. The great periods of cold 

 temperature should therefore follow at some distance the great periods of elevation 

 of the crust of the earth. The recent great glaciation followed at a notable in- 

 terval the great uplifts of the tertiary era. The great glaciation of India, Aus- 

 tralia, and South Africa came at about the time of the great disturbances closing 

 the palaeozoic era, but the precise relation cannot be positively stated. There 

 seem to be other correspondences between the laws here laid down and the great 

 climatic episodes of past geologic times. 



Another source of atmospheric loss arises from the removal of carbonic acid by 

 plants, aud the failure of this to be returned by decay or the action of animals. 

 It is estimated that the present annual growth of vegetation is sufficient to con- 

 sume all the carbonic acid in the air in one hundred years if there were no return. 

 It is believed that cold temperature would check the decay of vegetation and pre- 

 vent, in part, the return of the carbon to the atmosphere, and this would tend to 

 impoverish it. 



Tyndall suggested, fifty years ago, that the glacial periods might be due to 

 scantiness of carbonic acid in the atmosphere. Dr. Arrhenius has recently made 

 elaborate computations on the subject, and has reached the conclusion that the 

 removal of from 38 to 45 per cent, of the carbonic acid would bring on such a 

 glaciation as occurred in the ice age, and that an increase of two and a half to three 

 times the present carbonic acid would bring on a mild temperature, like that of 

 tertiary times. This view leaves the oscillations of the glaciation to be accounted 

 for. It is suggested that a rhythmical movement in the feeding and robbing of the 

 atmosphere would result from the action of the ocean and of the organic cycle. 

 The ocean, when cold, absorbs more carbonic acid than when warm, and hence, 

 instead of coming to the rescue of the atmosphere when robbed of its carbon 

 dioxide by the rocks, it was disposed to hold its carbonic acid, and perhaps even 

 turn robber itself. At the same time, the vegetation was less subject to decay, 

 and a smaller part of the carbon was returned to the air. By the combination of 



