THE CHEMISTRY OF THE ROCKS. 703 



of the chloride of sodium — common salt. Apparently in this one in- 

 stance the oxide is the less stable compound. 



But if, as we have endeavored to prove, there is a necessity of ac- 

 counting, in accordance with this theory, for the various compounds 

 and phenomena with which geology makes us familiar, then it is in 

 the highest degree essential that experiment and research be prose- 

 cuted in this new field. And there must be no hesitation in accepting 

 the conclusions to which they lead. Should the nebulous origin of 

 one planet be thus established by internal and inductive evidence, 

 then the nebular theory of the formation of worlds, which has hereto- 

 fore been received as only a provisional hypothesis, must be accepted 

 as having a scientific basis. If the earth has once been a self-luminous 

 body, in all respects excepting size, like the sun of to-day, it follows 

 from analogy that the other planets have likewise been minor suns 

 which have become extinguished by the burning out of their mate- 

 rials. To an observer on any unseen world among the stars, our sun 

 should have appeared in those times as a brilliant double, or mul- 

 tiple star, around which nine lesser companions have shone out for 

 a season, and then one after the other folded themselves up in 

 darkness. 



Furthermore, the study of this subject may throw light on many 

 cosmical problems — may tell us in earth-periods, if not in years, how 

 old the sun is when his glowing vapors begin to condense into dark 

 clouds ; and perhaps, too, something of his future prospects as a 

 luminary. It is remarkable that the spectrum has never shown any 

 indications of free oxygen in the atmosphere of the sun. Is not the 

 absence of this element further corroborated by the fact that the solar 

 spots, which there is evidence to believe are condensing clouds of iron 

 and calcium, do not glow with fierce burning, as they would if oxygen 

 were present ? Does not the enormous volume of the sun's uncom- 

 bined hydrogen indicate that it has not found, then, the element of its 

 strongest affinity ? And is there not reason to believe that the heat 

 and light supplies of our great luminary will last all the longer for the 

 absence of this most extravagant fire-generator ? 



Again, the four outer planets of our system have specific gravities 

 varying but little from that of water. Considering central condensa- 

 tion from pressure, it is probable that they are not so dense as they 

 would be if composed of the lightest compound substance that we 

 know of. If oxygen had been there in excess, it would long ago have 

 burned and condensed their elements, whatever they might be, into 

 most stable and solid forms. This gas, therefore, cannot have formed 

 any considerable part of their constitution. Is it not, then, a probable 

 supposition that these distant planets are composed of some non-com- 

 bining and inactive elements like nitrogen, and that, undisturbed by 

 combustions or elemental agitations, they have quietly stratified into 

 gaseous worlds, retaining in great part their original heat ? So far 



