464 Transactiovs. — Geology. 



can thus be held in sohition in the atmosphere at any given temperature is 

 fixed and invariable. But the quantity has not been found to be at any 

 known temperature, and increases rapidly Avith increase of heat. Since, 

 however, the quantity of water which the air can hold in solution at any 

 temperature is fixed, it follows that when that temperature is reduced the 

 superfluous water must be yielded up and deposited in the liquid form, such 

 deposition, in the large scale of nature, usually constituting rain. 



The question, however, naturally arises, whence has our globe derived 

 its large supply of water ? Now, this question has been fully considered by 

 Mr. W. Mattieu Williams, in his admirable work " The Fuel of the Sun," 

 and I make no apology to you for giving the substance of what he says on 

 the subject almost in his own words. After pointing out his reasons for 

 believing in the existence of an infinite atmosphere, of which the atmosphere 

 surrounding our planet is but a denser portion, and after discussing the 

 difference of atmospheric pressure at the surface of the various bodies 

 constituting our solar system, he asks whether we are to consider the water 

 which covers the lower valleys of the earth as planetary or atmospheric 

 matter ? Whether it is one of the special constituents of our globe or only a 

 portion of the general atmospheric matter which the earth's gravitation has 

 condensed round it ? He then proceeds to discuss these questions by 

 reference to those known properties of water, to which *I have already 

 alluded, which show that the position occupied by water on our own or any 

 other planet is entirely dependent on comparatively moderate variations of 

 temperature and pressure. "If," as he observes, "the temperature of the 

 earth were raised or the pressure diminished in a sufficient degree, the 

 whole of the water of the ocean would rise from its present bed and take its 

 place in the atmosphere as one of its constituent gases, and would there 

 exist in a state corresponding to the carbonic acid of our actual atmosphere." 

 Indeed, after fully considering the matter, he comes to the conclusion, — a 

 conclusion so fairly demonstrated as to be, in my opinion, irresistible, 

 "that the water upon our earth is but a portion of the matter which its 

 gravitation has collected from the all-pervading medium of the universe," 

 and he adds that there is good reason to believe that gaseous water is one 

 of the most important constituents of that general atmospheric medium, 

 and probably constitutes a considerable percentage of the whole. He 

 further observes that the spectrum analysis has afforded the strongest 

 possible confirmatory evidence of an universal distribution of water, for 

 that, whether directed to the sun, to the stars, to the nebulae, or to 

 the luminous matter of comets or meteors, the general reply is, "Water, 

 water, water everywhere;" Professor Graham having even found occluded 

 hydrogen in meteoric stones that have reached the earth, Mr. Williams 



