EAIXS AND EIYEES. 123 



have, encircling the earth, a belt of ocean thi'ee thousand miles in 

 breadth, from which this atmosphere hoists up a layer of water 

 annually sixteen feet in depth. And to hoist up as high as the 

 clouds, and lower down again all the water in a lake sixteen feet 

 deep, and three thousand miles broad, and twenty-four thousand 

 long, is the yearly business of this invisible machinery. What a 

 powerful engine is the atmosphere ! and how nicely adjusted must 

 be aU the cogs, and wheels, and springs, and com])ensations of this 

 exquisite piece of machinery, that it never wears out nor breaks 

 do^^^l, nor fails to do its w^ork at the right time and in the right 

 way ! The abstract logs at the Observatory in "Washington show 

 that the water of the Indian Ocean is warmer than that of any 

 other sea ; therefore it may be inferred that the evaporation from it 

 is also greater. The North Indian Ocean contains about 4,500,000 

 square miles, w^hile its Asiatic water-shed contains an area of 

 2,500,000. Supposing all the rivers of this water-shed to dis- 

 charge annually into the sea four times as much w^ater as the 

 Mississippi (§ 274) discharges into the Gulf, we shall have an- 

 nually on the average an effective evaporation (§ 282) from the 

 North Indian Ocean of 6.0 inches, or 0.0165 per day. 



301. The rivers of India are fed by the monsoons, which have to 

 The rivers of ludia, do their work of distributing their moisture in about 

 ""^Vil^^eZ'^^L. tt^ee months. Thus we obtain 0.065 inch as the 

 tionfrom that ocean, average daily rate of effective (§ 282) evaporation from 

 the warm waters of this ocean. If it were all rained down upon 

 India, it would give it a drainage w^hich would require rivers having 

 sixteen times the capacity of the Mississippi to discharge. Never- 

 theless, the evaporation from the North Indian Ocean required 

 for such a flood is only one sixteenth of an inch daily throughout 

 the year.* Availing myself of the best lights-^dim at best — as 

 to the total amount of evaporation that annually takes place in the 



* In his annual report of the Society (Transactions of the Bombay GeograpMcal 

 Society from May, 1849, to August, 1850, vol. ix.), the late Dr. Buist, the secretary^ 

 stated, on the authority of Mr. Laidly, the evaporatiouat Calcutta to be " about fifteen 

 feet annually ; tliat between the Cape and C/alcutta it averages, in October and 

 November, nearly three-fourths of an inch daily ; between 10^ and 20° in the Bay 

 of Bengal, it was fu.und to exceed an inch daily. Supposing this to be double the 

 average throughout the year, we should," continues the doctor, " have eighteen 

 feet of evaporation annually." All the heat received by the intertropical seas from 

 the sun annually would not be sufficient to convert into vapour a layer of water 

 from them sixteen feet deep. It is these observations as to the rate of evapora- 

 tion on shore tliat have led (§ 280) to such extravagant estimates as to the rate 

 at sea. 



