672 GEOLOGY. 



These results are subject to some qualification because certain of the experi- 

 mental conditions differed somewhat from those of the atmosphere, but they 

 seem to be the nearest approach to natural conditions yet attained in experi- 

 mentation. From the results, Arrhenius estimates that about 28% of the earth's 

 radiation is absorbed (oblique transmission included), and that the carbon dioxide 

 of the atmosphere influences the earth's temperature to the extent of 14.5° C. 

 Angstrom has estimated the absorption of carbon dioxide as at best only 16% 

 of the earth's radiation. 1 From the percentage curves of Rubens and Aschkinass, 

 applied to an energy curve determined by Angstrom, we deduce about 8% absorp- 

 tion by carbon dioxide, 2 but the deduction is subject to several rather serious 

 sources of probable error. 



From Angstrom's experiments, the following absorption values have been 

 deduced 3 for water- vapor : 



Amount of absorption 5% 10% 15% 20% 25% 



Amount of vapor traversed (measured as water in cm.) 0.3 0.85 2.1 4.2 6.8 



Owing to the differences of temperature, of the quantities used, of the degrees 

 of compression, and of other conditions involved in the experiments, on the 

 one hand, and to the lack of adequate data as to the average amount and dis- 

 tribution of moisture in the air, on the other, it is impracticable at present to 

 deduce the relative values of the thermal absorption of the water-vapor and 

 of the carbon dioxide of the present atmosphere, respectively, but it seems clear 

 that the efficiency of the vapor is several times that of the dioxide. 



The time of retention. — There is a defect in all the experimental work in 

 that it does not show the secondary or retentional effects of added quantities 

 of the gases. If a given quantity of gas absorbs 90% of all the radiation which 

 that gas can absorb by selective action, the addition of a second quantity of 

 equal amount could only selectively absorb, at -first hand, its proper proportion 

 of the 10% that had escaped previous absorption, but it would absorb secondarily, 

 heat radiated from the previously absorbed 90%, and delay its escape, as well 

 as radiate a portion of it back toward its source. It is not the simple absorption 

 of heat that determines the climatic effect, but the time of its retention, or, in 

 other words, the number of secondary absorptions and radiations. A given 

 quantity of vibratory energy retained ten seconds within the basal stratum 

 of the air by a series of re-absorptions and re-radiations, is as effective, climatic- 

 ally, as ten times the amount retained one second. While increase in the amount 

 of a gas does not proportionately increase the percentage of primary absorption 

 of the vibrations of its appropriate wave-lengths, it increases about propor- 

 tionately the number of times these are absorbed and re-radiated before they 

 finally escape. 



1 Ann. Phys. u. Chem., 1900, p. 324. 



2 Ann. Phys. u. Chem., 1898, p. 598. 



3 Kosmische Physik, II, p. 505. 



