DR. HAROLD JEFFREYS ON TIDAL FRICTION IN SHALLOW SEAS. 
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running strongest; and a similar velocity is recorded at the Burong Islands some 
distance to the north. As the depth of the passage between Borneo and Sumatra is 
fairly uniform, from 10 to 20 fathoms, these measures are probably typical of the 
whole. Quantitative estimates of the currents in the Gulf of Siam are few, and a 
reasonable guess at them would be difficult. The depth is mostly about 30 fathoms, 
but there are a deeper area in the middle and many shoals about the margins. As the 
current at the mouth of the gulf is across it, the tide in the gulf can arise only from 
the reflection of this by the Malay coast, so that the general set of the current is 
across the gulf, and considerable magnification in the gulf is unlikely. Our estimate 
of the dissipation will probably be of the correct order of magnitude, if we suppose 
that everywhere west of a line joining Cape Datu to Cambodia Point the maximum 
current is two knots. The area of this region is 8x10° sq. km. ; thus the maximum 
dissipation is 1*7 x 10 19 ergs per second. The velocity is proportional to the sine of 
the hour angle of the moon increased by a constant ; and as the dissipation is 
proportional to the cube of the velocity, the average dissipation is obtained by 
VOL. CCXXI,-A. 2 M 
