76 



Discussion. 



A. P. Carman spoke of the kinetic theor}' of gases and the 

 mathematical assumptions made when we go beyond the very- 

 simple applications of that theory. The discussion of the es- 

 cape of gas molecules from the earth's atmosphere involves as- 

 sumptions of the rate of fall of temperature with height in the 

 atmosphere. Extended experimental data on that subject are 

 limited to a few stations, and then to a height of only two or 

 three miles. The theory also calls for a change in the compo- 

 sition of the atmosphere as we go onward. The diagrams of 

 Henrich and of Ferrel based on the dynamical theory of gases 

 show that at comparatively small heights the percentage of the 

 lighter gases of the atmosphere should increase measurably ; and 

 yet an observation at nine miles is on record, which shows no 

 difference in the percentage of composition of the air at that 

 height from the earth's surface. This can of course be ex- 

 plained as due to the mixture of the different atmospheric 

 layers by currents ; but it leaves us without confirmatory experi- 

 ments. The rate of escape of the lighter gases from the earth's 

 atmosphere, even according to mathematical physicists who al- 

 low that it can take place at all, is very small. Much data are 

 therefore needed before we can speak with any great confidence 

 of what takes place at the outer layers of the earth's atmosphere. 



John M. Coulter said : 



In considering the adjustment of plants to the present atmos- 

 phere, it is interesting to remember that there are plants ex- 

 isting, notably among the bacteria, which can live without free 

 oxygen, which can manufacture carbohydrate food without 

 chlorophyll or light, which can use free nitrogen, and which are 

 remarkably resistant to external conditions that destroy other 

 plants. This is suggestive of the possibilities of plant life under 



