28 Proceedings of the Royal Physical Society. 



Latest of all the constituents of the Earth to pass from the 

 gaseous state were those which now form the hydrosphere. 

 At the stage of planetary evolution when the waters of the 

 ocean were yet floating in a vaporous condition as cloud- 

 belts surrounding a red-hot globe, our planet must have 

 borne a certain external resemblance to Jupiter as it appears 

 to-day. 



With the rocks at the surface of the primitive lithosphere 

 remaining at a high temperature, and with the waters of its 

 present oceans still in the clouds, the nascent Earth must 

 have been surrounded by an envelope largely composed of 

 the chlorides of various bases, and other compounds volatile 

 at a comparatively low temperature. This must have 

 hovered for a long time midway between the nascent litho- 

 sphere and the heavy cloud-belts above. It requires no 

 great stretch of the imagination to enable one to form some 

 conception of what was passing while the nascent Earth was 

 yet in this stage of evolution. The cloud-belt must have 

 congealed into snow on its outer surface, and must have 

 been continually condensing into rain in its zones beneath. 

 Such rain (like much that is generated in the summer time 

 even now) probably never reached the Earth's surface at all 

 in the earlier stages of this phase of its evolution ; but it 

 rose again and again as aqueous vapour, returning each time 

 to a slightly lower level above the Earth. As the cooling 

 progressed, the products of condensation did at last reach 

 the Earth, passing through the lower atmospheric envelope, 

 containing the chlorides, etc., as they did so. At a period 

 later still, the cooling surface was no longer sufiSciently hot 

 to drive the water back again into the clouds as aqueous 

 vapour. Hence the mixed solutions of chlorides in the water 

 from the clouds accumulated in the primeval depressions of 

 the lithosphere, and the oceans were the result. 



Thus the sea became salt from the first. 



Passing on now from the astronomical phase of the 

 Earth's development to the stage at which we find it to-day, 

 we may profitably inquire regarding what changes are affect- 

 ing the salt of the sea now. Leaving for the present the 



