340 Dr George Buist on the 



not much risk of its having fallen beforehand in the way of 

 the general reader. 



4 ' It is more than probable that besides the currents occa- 

 sioned by the trade-winds, monsoons, and sets of the tides — 

 we have a group of movements intermingled with these,'' 

 dependent mainly on evaporation. When it is remembered 

 that on the western shore of the Arabian Sea, including in 

 this the Red Sea and Persian Gulf, from the line northward, 

 we have an expanse of coast of no less than 6000 miles, and 

 a stretch of country of probably not less than 100 miles in- 

 land from this, where the average fall of rain does not amount 

 to four inches annually, where not one-half this ever reaches 

 the sea, and where to the best of our knowledge, the eva- 

 poration over the ocean averages at least a quarter of an inch 

 daily all the year round, or close on eight feet annually, some 

 idea of the enormous abstraction of water in the shape of va- 

 pour may be formed. On the assumption that this extends no 

 further, on an average, than 50 miles out to sea, we shall have 

 no less than 39 cubic miles of water raised annually in vapour 

 from the northern and north-western side of the basin, which 

 must be supplied from the open ocean to the south, or the rains 

 on the east. The fall of rain on the western side of the ridge 

 of the mountain chain from Cape Comorin to Cutch averages 

 pretty nearly 180 inches annually, and of this at least 160 

 is carried oif to the sea : that on the Concan to 70 inches, of 

 which probably 30 flow off to the ocean ; or betwixt the two 

 over an area of twenty miles from the sea-shore to the Ghauts, 

 and about 1200 miles from north to south, or an area of 

 24,000 square miles in all, we shall probably have an ave- 

 rage discharge of nine feet, or close on forty cubic miles of 

 water, — an amount sufficient, were it not diffused, to raise 

 the sea on our shores three feet high over an area of 72,000 

 square miles. 



The waters of the ocean cover nearly three-fourths of the 

 surface of the globe ; and of the thirty-eight millions of miles 

 of dry land in existence, twenty-eight millions belong to the 

 northern hemisphere.* The mean depth of the ocean 



* Since t bo above was written, Lieutenant Walsh, of the United StatesNavy, 

 has Bounded to the depth of about six miles, and in Oetober 1852, soundings 

 were mad" in Lat. 46 49' >S., long. 37' 6' \V., from on board Her Majesty's Ship 

 Herald, with an American line, to the depth of 7706 fathoms, or above 7 miles. 



