XVI 



JOURNAL R. A. S. (CEYLON). 



[Vol. III. 



I trust I shall not be for a moment supposed inclined to criticize, 

 much less to correct, this admirable and obviously most attractive work. 

 T have taken some texts from it, from which to give some brief 

 discourses on points of natural history which seem of interest, and which, 

 though perfectly familiar to the old Indian, seem scarcely to have 

 reached the English naturalist at all. 



I have seen in the Athenceitm of this morning the interesting letter of 

 Dr. Buist, dated Allahabad, June 10, in which exception is taken to a 

 passage in my recently published work on Ceylon, where I have 

 ventured to offer a simpler solution of the phenomenon of the steady 

 supply of fresh water in wells sunk in coral islands, than that heretofore 

 resorted to, — namely, the conjecture that the flow consists of rain-water 

 imbibed from the surface, and banked in by the surrounding pressure 

 of water from the sea. This theory, which was first broached in 

 Admiral ,FitzRoy's "Voyages of the Adventure and Beagle," and in 

 Darwin's " Naturalist's Journal," is thus propounded in the latter, when 

 speaking of the Keeling Islands, in the Indian Ocean, south-west of 

 Sumatra, one of those "atoll" groups, in the islets of which there are 

 wells from which ships obtain water: — " At- first sight," says Darwin, 

 " it appears not a little remarkable that the fresh water should regularly 

 ebb and flow with the tides ; and it has even been imagined that sand 

 has the power of filtering the salt from the sea-water * * The com- 

 presed sand, or porous coral rock, is permeated like a sponge with the 

 salt water ; but the rain which falls on the surface must sink to the 

 level of the surrounding sea, and must accumulate there, displacing an 

 equal bulk of the Salt water. As the water in the lower part of the 

 great sponge-like mass rises and falls with the tides, so will the water 

 near the surface ; and this will keep fresh, if the mass be sufficiently 

 compact to prevent much mechanical mixture." — .Darivin's "Naturalist's 

 Journal" chap. x.\. Dr. Buist's explanation corresponds with that of 

 Darwin ; but Darwin, as it will he seen, glances at, although he rejects 

 the theory of filtration from the sea ; whilst Dr. Buist urges, that 

 "Nothing is more utterly opposed to the first principles of physics than 

 the doctrine that salt held in solution by water should be capable of 

 being separated from it by the mere mechanical process of filtration." 

 Dr. Buist, however, is not aware that since Darwin wrote, the late Mr. 

 Will, in a remarkable paper published in the Philosophical Magazine 

 for 1856, " On a Peculiar Tower possessed by 1'orous Media of removing 

 Matters from Solution in Water " has made known the results of 



Geo. Buist. 



London, August 11, 1860. 



