818 PRINCIPLES OF CHEMISTRY 



when coming into proximity with it during their motion in space. The 

 meteoric dust, on passing through the upper parts of the atmosphere, 

 and becoming incandescent from friction with the gases, produces that 

 phenomenon which is familiar under the name of falling stars. 2 Such is 



2 Comets and the rings of Saturn ought now to b6 considered as consisting of an 

 accumulation of such meteoric cosmic particles. Perhaps the part played by these 

 minute bodies scattered throughout space is much more important in the formation 

 of the largest celestial bodies than has hitherto bean imagined. The investigation of 

 this branch of astronomy, due to Schiaparelli, has a bearing on the whole of natural 

 Science. 



The question arises as to why the iron in meteorites is in a free state, whilst on earth 

 it is in a state of combination. Does not this tend to show that the condition of our 

 globe is very different from that of the rest? My answer to this question has been 

 already given in Volume I. p. 877, Note 57. It is my opinion that inside the earth there 

 is a mass similar in composition to meteorites that is, containing rdcky matter and 

 metallic iron, partly carburetted. In conclusion, I consider it will not be out of place 

 to add the following explanations. According to the theory of the distribution of pres- 

 sures (sae my treatise, On Barometrical Levelling, 1876, pages 48 et scq.) in an atmo. 

 sphere of mixed gases, it follows that two gases, whose densities are d and d lt and whose 

 grelative quantities or partial pressures at a certain distance from the centre of gravity 

 Are h and h^ will, when at a greater distance from the centre of attraction, present a 

 -different ratio of their masses x : a^ that is, of their partial pressures which may be 

 found by the equation fZ^log h log x) d(\og h\ log Xi). If, for instance, d : di = 2 : 1, 

 and h = hi (that is to say, the masses are equal at the lower height) = 1000, then when 

 # = 10 the magnitude of Xi will not be 10 (i.e. the mass of a gas at a higher level whose 

 density =1 will not be equal to the mass of a gas whose density =2, as was the case at 

 a lower level), but much greater namely, x l = 100 that is, the lighter gas will pre 

 dominate over a heavier one at a higher level. Therefore, when the whole mass of the 

 earth was in a state of vapour, the substances having a greater vapour density accumu- 

 lated about the centre and those with a lesser vapour density at the surface. And as 

 the vapour densities depend on the atomic and molecular weights, those substances which 

 "have small atomic and molecular weights ought to have accumulated at the surface, and 

 those with high atomic and molecular weights, which are the least volatile and the easiest 

 to condense, at the centre. Thus it becomes apparent why such light elements as 

 liydrogen, carbon, nitrogen, oxygen, sodium, magnesium, aluminium, silicon, phosphorus, 

 sulphur, chlorine^ potassium, calcium, and their compounds predominate at the surface 

 .and largely form the earth's crust. There is also now much iron in the sun, as spectrum 

 analysis shows, and therefore it must have entered into the composition of the earth 

 And other planets, but would have accumulated at the centre, because the density of 

 its vapour is certainly large and it easily condenses. There was also oxygen near the 

 centre of the earth, but not sufficient to combine with the iron. The former, as a much 

 lighter element, principally accumulated at the surface, where we at the present time 

 find all oxidised compounds and even a remnant of free oxygen. This gives the 

 possibility not only of explaining in accordance with cosmogonic theories the pre- 

 dominance of oxygen compounds on the surface of the earth, with the occurrence of 

 unoxidised iron in the interior of the earth and in meteorites, but also of understanding 

 why the density of the whole earth (over 5) is far greater than that of the rocks (1 to 3) 

 composing its crust. And if all the preceding arguments and theories (for instance 

 the supposition that the sun, earth, and all the planets were formed of an elementary 

 homogeneous mass, formerly composed of vapours and gases) be -true, it must be ad- 

 mitted that the interior of the earth and other planets contains metallic (unoxidised) iron, 

 which, however, is only found on t'ae surface as aerolites. And then assuming that 

 .aerolites are the fragments of plrnets which have crumbled to pieces so to say 

 .during cooling (this has been held to be the case by astronomers, judging from the paths 



