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SCIENCE. 



[N. S. Vol. XII. No. 293. 



during its history, contained many thou- 

 sands of times its present amount of carbon 

 dioxide, as is implied by the vast stores 

 of carbon and carbonates that have been 

 removed from it. We are thus driven to 

 assume either that the early atmosphere 

 was very rich in carbon dioxide, and has 

 been impoverished as the ages have gone 

 on, or that the loss has been made good by 

 supplies received concurrently. In the for- 

 mer case glaciation and similar phenomena 

 dependent on an impoverished atmosphere 

 should be confined to the later ages. But 

 the most extraordinary glaciation of vrhich 

 we have any knowledge took place near 

 the close of the Carboniferous period, or, 

 in other words, far back in the geological 

 series. Vast beds of limestone, coal, and 

 other carbonaceous deposits have since been 

 formed at the expense of the atmosphere's 

 carbon dioxide. Much oxygen and some 

 nitrogen have also been consumed, but we 

 need not dwell on these. If all this carbon 

 dioxide had been in the atmosphere at that 

 time there is reason to doubt whether the 

 glaciation of India, Australia and South 

 Africa could have taken place. Besides, 

 in the Permian and Triassic periods great 

 salt and gypsum beds were laid down over 

 many degrees of latitude and longitude on 

 both continents. These imply an aridity 

 of surprising extent, duration, and intensity, 

 reaching to latitudes not at present affected 

 by appreciable excess of evaporation over 

 precipitation. If the atmosphere had been 

 rich in carbon dioxide, which is believed to 

 equalize temperature and humidity, there 

 is reason to doubt whether these deposits 

 could have been formed. But even still 

 earlier, as far back as Silurian times, before 

 the coal of the Carboniferous period or the 

 carbon dioxide of the great limestones 

 of the Subcarboniferous and the Devonian 

 times had been taken out of the atmosphere, 

 widespread and thick salt beds were formed 

 in the St. Lawrence basin where now the 



excess of precipitation forms great lakes 

 and a mighty river. Nor is even this the 

 earliest evidence of notable aridity. 



Now these and allied phenomena, which 

 imply extraordinary inequalities of atmos- 

 pheric states, call for a reconsideration of 

 inherited views regarding the constitutional 

 history of the atmosphere. To suppose 

 simply that the atmosphere was once ex- 

 ceedingly rich in carbon dioxide and has 

 been steadily impoverished does not seem 

 to fit the phenomena. But when once a 

 reconsideration is undertaken there is no 

 stopping place short of the original state of 

 the atmosphere, and we are at once in- 

 volved in the pros and cons of the nebular 

 hypothesis. 



If the nebular hypothesis is approached 

 from the atmospheric side, we must carry 

 into the inquiry the modern kinetic theory 

 of gases or give reasons for dissenting from 

 its validity. In framing the nebular hy- 

 pothesis a century ago Laplace could not 

 call to his aid the present dynamic concep- 

 tion of gases, and, while this absolves him 

 from responsibility, it makes it the more fit- 

 ting that the hypothesis should be tested by 

 the kinetic views that have grown out of re- 

 searches since his day. These views may 

 perhaps require modification in the future, 

 but such modification is more likely to 

 involve intensified molecular activity than 

 the opposite. 



Led thus to the subject, we have at- 

 tempted to make a test of the nebular hy- 

 pothesis by a comparison of the molecular 

 velocities of the essential gases with the 

 gravitative power of the earth, and its an- 

 tecedent nebulous ring, to control these at 

 the temperatures assigned them by the hy- 

 pothesis. We have followed the general 

 method employed by Dr. Johnstone Stoney 

 in discussing the atmospheres of planets and 

 satellites.* The essence of the method is 



* ' On the Cause of the Absence of Hydrogen from 

 the Earth's Atmosphere and of Air and Water from 



