Carbon Dioxide as a Constituent of the Atmosphere. 387 



depends on the properties of the layer forming the component 

 of the pair nearest to the kathode ; or, shortly, each layer, or 

 the conditions existing at its point of origin, always influence 

 the layer following next to it, on the side of the anode, but 

 does not influence the preceding, on the side of the kathode. 

 The conditions under which the nth. layer forms seem to 

 stand to the properties of the n + 1th layer in the relation of 

 cause and effect ; and hence it seems to me only a verbally 

 different expression of the observed facts if we assume, as above, 

 that the propagation of the electrical tensions, or the produc- 

 tion of the separate layers, takes place in the direction of in- 

 creasing values of n, i. e. advances from the kathode towards 

 the anode. 

 Berlin, Physical Institute of the University. 



XLII. Carbon Dioxide as a Constituent of the Atmosphere. By 

 Eknest H. Cook, B.Sc. (Lond.), A.R.C.S., Lecturer upon 

 Chemistry and Physics at the Bristol Mining School*. 



OF all the agents which have brought about geologic 

 changes and modified the surface of the earth from time 

 to time, the atmosphere seems to have been the least studied. 

 Nor is this very surprising when we remember the peculiarity 

 of its action. So general and cosmopolitan are its effects that 

 their very abundance causes us to overlook them — and, again, 

 so slowly acting that the changes effected require the employ- 

 ment of long periods of time. The two constituents of the 

 atmosphere which have been most active in producing these 

 changes are the oxygen and the carbon dioxide. The latter 

 substance occurs in the air in such a relatively small amount 

 that we are apt to underrate its influence. But when it is 

 remembered that, were it not for the presence of this sub- 

 stance in the air, no coal and very little limestone could have 

 been formed, we at once see its importance. In fact, to come 

 somewhat nearer home, without carbon dioxide in air no vege- 

 table growth could take place ; and without plant life very 

 little, if any, animal life would occur. Thus this substance, 

 although in itself inimical to most forms of animal life, is 

 absolutely necessary in the atmosphere in order that those 

 animals may exist. In the present paper an attempt is made 

 to consider some of the results arising from the presence of 

 this substance. 



* Head before the American Association for the Advancement of Science 

 at Montreal, on August 25, 1882. Communicated by the Author. 



