18G0.] Memorándum on tlie Irawadi Biver. 179 



struck the river. The fact that the Irawadi was then only 8*0 yards 

 broad and fordable, is absolutely conclusive regarding the small 

 volume of its water, and should I think be equally so regarding the 

 near vieinity of its source. 



10. The minimum discharge of the Irawadi is differently stated by 

 the only two observers who have yet published their measurements. 

 On 25th April, 1853, Dr. McClelland found the breadth of the 

 river at Prome to be 3,630 feet with a mean depth of 12'7083 feet, 

 giving a sectional área of 40,131*129 square feet. The velocity of 

 the current was lfl miles per hour, or 2'8666 feet per second. Dr. 

 McClelland calis this the " mean speed." This measurement refers 

 to the surface velocity and not to the average velocity of the mass, 

 to obtain which he multiplies the above mean speed by 8, and 

 makes the discharge 105,794 cubic feet per second. But the for- 

 mula for obtaining the average velocity of the mass which is given 

 by Cape, and by Jackson, the Secretary of the Boyal Geographical 

 Society, as determined from the experiments of Du Buat, yields a 

 very difíerent result. By this formula the velocity of the mass, 



(¿S— l) 2 -{-S 

 M= =S — ^/íS-f'5, where S=the surface velocity of the 



stream. By using this formula, the mean velocity of the mass of 

 water is reduced to 1*67352 foot per second, which yields a discharge 

 of 77,201-151 feet per second. But as the river fell fifteen inches 

 after the date of Dr. McClelland's measurement, this amount has to 

 be brought still lower by deducting 125 foot from the mean depth 

 of 12-7083 feet. This will cause a reduction of 7592 760 cubic feet, 

 and thus make the minimum discharge of the Irawadi in 1853 at 

 Prome 69,608391 cubic feet. 



11. The other measurement of the Irawadi was taken by Mr. 

 T. Login, at the head of the Delta, just above the point where the 

 Bassein river branches ofT. The measurements were made I believe 

 in 1855, but the details have not been published. The result alone 

 is given, which makes the minimum discharge at the head of the 

 Delta at 75,000 cubic feet. 



12. On the 30th March, 1857, a third measurement of the Irawadi 

 was made at Meaday at my request, by Lieut. G. de P. Falconnet of 

 the Madras Enginecrs. This measurement was conducted with 



