On Inquiries as to the Escape of Gases from Atmospheres. 291 



energy as that indicated by some law. But if while this process is 

 matiiring a wind overthrows the tower, sweeping away the air it con- 

 tained and substituting other air under new conditions, and subject to 

 all the chances of uprushes, downrushes, thunderstorms, auroras, 

 cyclones, cloud, sunshine, rain, &c. ; then after all or any of these 

 or of the like accidents, the tower would have to be rebuilt before 

 any portion of the atmosphere extending from the bottom to the top 

 could find itself in a position even to commence the first steps of an 

 advance towards at some future time complying with the law. 



The supposition then that the Boltzmann-Maxwell law can be 

 restricted within our existing atmosphere would appear to be a mistake ; 

 and if so the inferences from that law are not part of a real interpre- 

 tation of nature. It need not therefore be matter of surprise that, in 

 the case of helium, the facts of nature seem to negative those inferences. 



The weather which will prevail over the earth this day month will 

 be the outcome of the present molecular state of the earth, and of the 

 molecular events which will happen in the meantime ; but our power 

 of stating in mathematical form the existing state of the earth, and our 

 knowledge of molecular physics, are not such as would enable us to 

 predict that future weather by the a pviwi or deductive method of 

 proof. The difficulties in this case are easily seen; and they are 

 instructive, since the escape of gas from the earth depends on pheno- 

 mena which are probably as complex as those which determine the 

 weather and as little amenable to treatment by the deductive method. 



Any such distribution of energy as that assigned by the Boltzmann- 

 Maxwell law would, if it could be realised, be brought into existence 

 by the gradual eftacement of excesses which had previously existed ; 

 from which it would appear to follow that excesses prevail in our 

 existing atmosphere greater and more numerous than could exist in an 

 ideal atmosphere that obeyed that law. It is probable, therefore, 

 that in our actual atmosphere there are more opportunities for the 

 escape of molecules than there would be in the ideal atmosphere 

 a conclusion which accords well with the fact that the actual rate of 

 escape exceeds those computed by Professor Bryan and Mr. Cook, 

 (See 'Nature' of May 24, 1900, p. 78, second column.) 



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