Decembeb 25, 1908] 



SCIENCE 



901 



and the waters, during the stages of active 

 terrestrial growth than at the present time, 

 when terrestrial activities have more 

 largely settled down into a state of less 

 disturbed equilibrium. The same may 

 doubtless be presumed of the unstable non- 

 volatile compounds of the critical elements, 

 but just here we are considering only the 

 factor which worked through the atmos- 

 phere. 



We have already denied ourselves any 

 special appeal to general atmospheric 

 pressure as an agency of the particular 

 synthesis in question, but in doing this we 

 have limited our abnegation to the sum 

 total of pressure. It is stiU pertinent to 

 inquire what may have been the effects of 

 partial pressure. Starting with the fa- 

 miliar postulate that each constituent of 

 a mixed gas acts in accordance with its 

 own individual partial pressure, it appears 

 that high partial pressures of the critical 

 constituents should have been more effect- 

 ive in causing their entrance into combina- 

 tion than high general pressure without 

 such high partial pressures. We have just 

 seen that the chemical and physical condi- 

 tions attending the stages of active earth- 

 growth might well have given rise to large 

 proportions of the critical compounds. By 

 extending the argument it is not difficult to 

 see that the actual amount of the carbon, 

 sulphur, phosphorus and nitrogen gases 

 might have been sufficiently greater than 

 now to have promoted their union, for they 

 all have high specific weights and could be 

 held in relatively large proportions by the 

 gravity of even a small earth. The 

 gaseous compounds of nitrogen have a 

 place in this class, though the free nitrogen 

 was probably less abundant than now, but 

 since free nitrogen is organically inert, it 

 is negligible except as a source of its com- 

 pounds. 



If we turn to the non- volatile or slightly 

 volatile compounds of the critical ele- 



ments, we find, as already remarked, rea- 

 son for thinking that there may have been 

 more of the unstable compounds of this 

 class than now, for secular progress would 

 be in the direction of chemical stability. 

 There are certain probable sources of un- 

 stable compounds of carbon, sulphur, phos- 

 phorus and nitrogen which call for special 

 notice. Planetesimals are only one form 

 of meteoroids and it is possible that the 

 meteorites which reach the earth in appre- 

 ciable masses may not often be true plane- 

 tesimals of the class supposed to have 

 formed the earth, but if the theory of 

 common meteorites advanced by the senior 

 author be the true one,° the compositions 

 of the two classes are probably much alike, 

 for according to this theory meteorites are 

 supposed to be the fragments of small 

 planetoidal bodies which have been dis- 

 rupted by close approach to large bodies. 

 These planetoidal bodies are supposed to 

 have been too small to hold atmospheres 

 and hydrospheres, and hence the planetesi- 

 mals which formed them were never sub- 

 jected to atmospheric and hydrospheric 

 agencies, and hence they retained their 

 planetesimal constitution with little modi- 

 fication.^ This furnishes ground for as- 

 suming that the compounds found in 

 meteorites were also present in the plane- 

 tesimals. This presumption finds support 

 in the nature of the ease, for the gases shot 

 forth from the sun to form the planetesi- 

 mals probably were much dissociated by 

 high temperature at the instant of emerg- 



'Asfrophys. Jour., Vol. XIV., 1901, pp. 17-40; 

 Jour. Geol, Vol. IX., 1901, p. 369, and Chamber- 

 lin and Salisbury's " Geology," Vol. II., pp. 22-38. 



' Dewar states that at a temperature of — 130° 

 C. liquid oxygen has no chemical action on hydro- 

 gen, potassium, sodium, phosphorus, etc. {Proo. 

 Roy. Inst., Vol. 11, 1884-ti, p. 550), and this is 

 perhaps an additional reason why planetesimals 

 and meteorites enveloped in the low temperatures 

 of space prevalent at considerable distances from 

 the sun have been subjected to little oxidation. 



