PRIMORDIAL OCEAN OF OUR GLOBE. 115 



terrestrial water existed as vapour floating as an atmosphere round 

 the dry and heated planet ; and unless we assume the altogether im- 

 probable notion of successive creations of additional water, the whole 

 of our existing oceans, and all the other water of our globe, must 

 have then hung in vapour above its surface, constituting the chiefly 

 aqueous, but partly aerial, atmosphere of the primordial globe. Por 

 want of numerical data, especially those relating to the pressure and 

 corresponding temperature of steam, and what the actual volume of 

 terrestrial and oceanic water was, we are unable to assign what the 

 temperature of our globe then was, though it must have been somewhat 

 higher than that of the. atmosphere above it, which was exposed to 

 cooling by radiation into space ; and in this state of equilibrium 

 between heat and gravitation the slightest reduction of temperature 

 must have been attended with condensation of vapour, and with the 

 first deposit of liquid water upon our earth. It is not an extravagant 

 supposition, therefore, that the first drops of liquid water which ever 

 rolled upon the surface of our globe were at a temperature possibly 

 equalling that of liquid cast iron. However high must have been 

 the boiling-point of water, while it was all compelled to remain sus- 

 pended as vapour by the repulsive power of the heated globe itself, 

 this last was then, as now, in process of gradually cooling by loss of 

 heat by radiation into interstellar space. With every such decre- 

 ment of temperature, watery vapour must have been condensed and 

 precipitated in a liquid state upon the earth's surface ; but with 

 every such stage of cooling and condensation less water vapour 

 floated above our globe, and less barometric pressure resulted. 

 Hence the boiling-point, or, what is the same thing, the temperature 

 of liquefaction of the remaining aqueous vapour, and of the liquid 

 water produced by previous condensation, must have receded until, 

 in the course of ages, the temperature of ebullition of water reached 

 what we now find it to be. The boiling ocean-water continued to 

 cool until its temperature, as known in historic time and now, was 

 reached ; and to this other and, in some respects, more complex con- 

 ditions than those to which we have already referred concurred, as 

 we shall presently see. "When we attempt to follow out the pro- 

 bable conditions that must have attended the gradual refrigeration 

 by radiation into space of a highly heated globe and a nearly 

 equally heated ocean, we are launched upon a mental voyage where 

 the imagination is often left without any sure guide from reason and 

 known natural laws ; still, amid so much obscurity, we can discern 

 some outlines which may be regarded as true. 



Upon the aerial conditions in relation to the heat and light 

 derived from the sun through an atmosphere composed almost 

 wholly of steam, I shall only remark that such an atmosphere would 

 be much more oblate in form than our present atmosphere, and also 

 much less penetrable by the solar rays, and would therefore produce 

 far greater vicissitudes, both of light and heat, between summer and 

 winter, than now exist. There would always be, as Buffon long 

 since indicated, a great difference of temperature between the polar 

 and equatorial regions ; so that during the later stages of the deposi- 



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