30 Proceedings of the Royal Physical Society. 



the surface of the Earth, whence it is carried down by rain 

 and snow, and is also dissolved by dew and extracted by hoar 

 frost. The analyses made by J. J. Pierre, in the neighbour- 

 hood of Caen, showed that a hectare of land received annually 

 from the atmosphere, by means of rain alone, the following : — 



and, in addition, sulphates of soda, potash, lime, and magnesia 

 to a total of 28-5 kilogrammes. 



The quantity present in any particular case varies, as 

 might be expected, with the distance of the place of 

 observation from the sea, rising above the amount men- 

 tioned in a few maritime areas, and falling below it in 

 districts which are situated far inland ; but these variations 

 are just what might have been expected under the circum- 

 stances. 



Furthermore, it can be shown that the sea-salt carried 

 down in rain and snow does find its way seaward by means 

 of rivers — being, indeed, in some cases, and to an unimportant 

 extent, augmented by chloride of sodium derived in various 

 other ways from the rocks of the land. There is no need to 

 give details in support of either of these points, which, I 

 suppose, no one will question. 



There are large areas of inland drainage upon the Earth, 

 amounting in the aggregate, according to Sir John Murray, 

 to 11,486,350 square miles, the area whence rivers flow to 

 the sea being, according to the same authority, 44,211,050 

 square miles. Eoughly speaking, therefore, the rainfall over 

 about one-fifth of the total surface of the land does not return 

 direct to the sea, but is, in large part, dissipated by evapora- 

 tion, and goes back into the atmospheric circulation direct. 

 The salts carried down from the salt-dust of the atmosphere 

 do not, in such areas, return to the sea, but are left on the 

 land. Furthermore, in the case of such rivers as the Nile, 



