Theory of Solar Action. 401 



The fundamental assumption of the existence of a universal 

 atmosphere, to which M. Faye so strongly objects, is one 

 which, it seems to us, both theoretical and experimental evi- 

 dence supports. But the deductions which are drawn from 

 this we do not think can be supported. It is supposed that 

 the atmospheres attracted by the planets would consist for the 

 most part of the " heavier and less diffusible gases — nitrogen, 

 oxygen, and carbonic anhydride ; whilst hydrogen and its 

 compounds would predominate in space." But if such a 

 partial separation takes place, we should expect that the 

 heaviest constituent of the universal atmosphere (viz. the car- 

 bonic anhydride) would exist in larger quantity in the plane- 

 tary atmospheres. More especially should we do this when 

 we remember the great difference in the relative density of 

 C0 2 and and N. Also, if such a selective attraction takes 

 place, we ought to find a slight difference in the composition 

 of the air at high altitudes and at low ones. Saussure, who 

 has investigated this point, states that at high altitudes the 

 proportion of dioxide is generally greater than at lower levels 

 (Pogg. Ann. xix. p. 391). Among other investigators we 

 may mention "Gay Lussac and Thenard, who collected air 

 in a balloon at an elevation of 7000 metres, and found it to 

 contain exactly the same proportional quantity of oxygen as 

 that collected at the same time in Paris and analyzed in the 

 same way. Their results have since been corroborated by the 

 more exact investigations of Brunner, who analyzed the air 

 collected at the top and at the bottom of the Faulhorn, and 

 found in each case exactly the same proportion between the 

 oxygen and the nitrogen"*. Also Frankland (Chem. Soc. 

 Journ. xiii. p. 22) has found that the composition of the air 

 up to altitudes of 14,000 feet is constant. We may thus con- 

 clude that, so far as terrestrial observation goes, there is abso- 

 lutely no evidence supporting the partial separation of the 

 constituents of the atmosphere supposed to take place. 



Dr. Siemens cites the composition of the gases found oc- 

 cluded in meteorites as supporting his view of the existence 

 of an atmosphere very rich in hydrogen existing in space. 

 There is also a general belief that the presence of these gases 

 under pressure proves that they have passed through a region 

 where hydrogen exists under a much greater pressure than 

 that of our own atmosphere. According to this view the gas 

 contained in the body is really a portion of the interplanetary 

 atmosphere; it ought therefore to consist largely of hydrogen, 

 while the proportion of the heavier gases should be much 

 smaller than that • existing in the air. But we find, on the 

 * Eoscoe and Schorlemmer, ' Chemistry,' vol. i. p. 440. 



