464 Transactions.—G eology. 
can thus be held in solution 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 with 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 atmospherie pressure at the surface of the various bodies 
constituting our solar system, he asks whether we are to consider the water 
whieh covers the lower valleys of the earth as planetary or atmospherie 
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 nebulx, 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 
