t>R, HAEOLD JEFFREYS ON TIDAL FRICTION IN SHALLOW SEAS. 
257 
36 km., and the depth 20 fathoms. The average flux of energy eastward past it is 
found to be 1‘OxlO 17 ergs per second. Thus the average excess of the inflowing 
energy over the issuing energy is 6 x 10 17 ergs per second. The work done by the 
moon is insignificant, for it crosses the meridian at full and change at 2h. 30m., which 
is nearly the average time of high water. Thus all the excess of energy just found is 
dissipated in the strait. 
The area of the strait between the Kumpei-Penang section and the Medang section 
is 56,000 sq. km. If the average current in this had an amplitude of 2 knots the 
dissipation would be 5xl0 17 ergs per second on an average, in striking agreement 
with the estimate from the flux of energy, though the latter is more reliable. If in 
the final estimate the region north of the Kumpei-Penang section is to be included, 
we must add a fraction to the total to allow for it, making probably between 8 x 10 17 
and 12 x 10 17 ergs per second in all. 
In the part of the strait east of Medang there are few records of the currents, but 
the dissipation is probably small. In any case it could not exceed the 10 u ergs per 
second that pass Medang, and is probably less than this. The total dissipation in the 
Strait of Malacca is therefore IT x 10 18 ergs per second, subject to an uncertainty of a 
fifth of its amount. 
Australian Waters. 
Australia is surrounded by a belt of water less than 100 fathoms in depth ; the 
width of this ranges from 10 to 200 miles, except at the Gulf of Carpentaria, where it 
extends right across to New Guinea. The tide in this neighbourhood is diurnal, like 
that in the South China Sea to the north of it. The contribution to the secular 
acceleration of the moon is accordingly very small. The tidal streams do not exceed 
1 knot, and as the area is much less than that of the South China Sea the dissipation 
in the diurnal tide cannot be comparable with that already found for the larger sea. 
African Waters. 
The Mozambique Channel. 
The channel between Madagascar and the mainland is mostly about 500 fathoms 
deep or more. There are few records of tidal currents in it; in fact the only record 
given in the ‘ African Pilot,’ part 3, appears to be based on the statement of a single 
observer, that the tidal streams in the channel are comparable with the permanent 
current driven by the trade winds, which flows at about 2 knots. This cannot 
however be uniform all over the channel, for the following reason. The height of the 
tide along the African coast is about 12 feet, which is as usual measured relative to 
low water at ordinary springs, so that the vertical amplitude of the tide is 180 cm. 
Now the ordinary theory of tides in channels shows that the maximum velocity is of 
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