272 



SCIENCE. 



[N. S. Vol. XXIII. No. 581. 



is never greater than that exerted by the 

 magnet. 



In the case of the earth and its atmosphere 

 Krafft has given us our first measurement of 

 the attractive force of the earth (gravity) 

 and the attractive force of the atmosphere for 

 the earth (atmospheric pressure) in the same 

 unit of measurement (degrees of heat). His 

 measurements show that the tvi'o are equal 

 and we must, therefore, conclude that the 

 present atmosphere of the earth is the largest 

 it is capable of holding. If from any source 

 additions were made to our atmosphere a cor- 

 responding amount would be thrown off, i. e., 

 escape from the atmosphere into space. ' The 

 portion thrown off would probably consist of 

 those molecules having the highest molecular 

 velocities lying in the upper strata of the at- 

 mosphere.^ 



The various theories of world formation all 

 give gravity a smaller value in the past than 

 it has at present. There is yet to be found 

 the first evidence tending to show that gravity 

 has ever been greater than at present. If 

 gravity has never been greater th'an at present 

 then from Krafft's results we must conclude 

 that the atmosphere of the earth can never 

 have been greater than the present atmosphere 

 and the atmospheric pressure never greater 

 than 760 mm. of mercury (14.7 pounds). 



We here find ourselves in decided disagree- 

 ment with the Laplacian hypothesis common- 

 ly accepted by geologists and astronomers. 



Geikie"' says : " It is certain that the present 

 gaseous and liquid envelopes of the planet 

 form only a portion of the original mass of 

 gas and water with which the globe was in- 

 vested. Fully half the outer shell or crust 

 of the earth consists of oxygen, which prob- 

 ably once existed in the primeval atmosphere." 



- Compare the articles on the conditions of the 

 escape of gases from the atmosphere, by G. John- 

 stone Stoney, in which he has shown that the 

 molecular velocities of hydrogen and helium are 

 so large that the earth is unable to retain them 

 in its atmosphere. Trans. Royal Dublin Hoc, 

 1892, p. 563; iUd., 1897, p. 305. Astrophys Jour., 

 Vlll. (1898), 310; XL (1900), 251 and 357; XII. 

 (1900), 201. 



"•Text-book of Geology," 4th ed., Vol. I., p. 34. 



Dana,* in discussing the subdivisions of 

 Archaean time, gives perhaps the best state- 

 ment of the prevalent view: 



The astral Econ, as it has been called, or that 

 of the fluid globe having a heavy vaporous en- 

 velope containing the future water of the globe or 

 its dissociated elements and other liea\'j' vapors 

 or gases. * * * The lithic era : commencing 

 with earth as a solid globe, or at least solid at 

 the surface; the temperature at the beginning 

 above 2,500° V.; the atmosphere still containing 

 all the water of the globe (amounting to 200 

 atmospheres, according to Mallet,'' 1880), all the 

 carbonic acid now in the limestone and that corre- 

 sponding to the carbon now in the carbonaceous 

 substances and organic substances (probably 50 

 atmospheres), all the oxygen since shut up in 

 the rocks by oxidation, as well as that of the 

 atmosphere and of organic tissues. 



Other calculations of the primeval atmos- 

 phere give it the same or even a greater extent, 

 e. g.j Prestwich" by a calculation later than 

 Mallet's reaches the same value for the water 

 vapor. T. Sterry Hunt' finds the carbonic 

 acid alone 200 times the present atmosphere. 



A small primeval atmosphere is just as 

 much out of harmony with the idea of the 

 formation of the globe by the contraction of 

 a quasi-gaseous swarm of meteorites, as sug- 

 gested by Lockyer and by Darwin,^ and with 

 all other hypotheses requiring for the earth 

 at any time a surface temperature above that 

 of boiling water, as it is with the Laplacian 

 hypothesis. It is, however, in excellent agree- 

 ment with the planetesimal hypothesis devel- 

 oped by Chamberlin and Moulton," in which 



"* ' Manual of Geologj',' 4th ed., p. 440. 



"■Quart. Jour. Geol. Soc, XXXVI., p. 112. 



"'Geology,' Oxford, 1886, Vol. I., p. 417. 



' Brit. Assoc. Rep., 1878, Trans., Sec. C, p. 544. 



' Compare Darwin's classic paper, ' On the Me- 

 chanical Condition of a Swarm of Meteorites and 

 on the Theories of Cosmogony,' Trans. Phil. Soc, 

 1888. 



° Best presented by Dr. Chamberlin in ' Funda- 

 mental Problems of Geology,' Year Book No. 3 

 (1905) of the Carnegie Institution of Washington, 

 pp. 195-258. Compare also Chamberlin, Jour. 

 Geol, V. (1897), p. 653; VIII. (1900), p. 58; 

 IX. (1901), p. 309; Moulton, Astrophys. Jour., 

 XI. (1900), p. 103; Chamberlin and Moulton, 

 Science, XIl. (1900), p. 201. 



