248 
DE. HAEOLD JEFFEEYS ON TIDAL FEICTION IN SHALLOW SEAS. 
multiplying the maximum by the average arithmetical value of sin 3 0 taken over a 
period, which is 4/3-7T. It is not clear what declination of the moon the recorded 
currents refer to : if they refer to the maximum, the average for the month will be 
found by multiplying again by 4/377. Thus the average dissipation of energy in the 
diurnal tide in the western part of the China Sea is of the order of 3 x 10 18 ergs per 
second. 
We next proceed to examine the dissipation in the main part of the South China 
Sea, between the north-west coast of Borneo and the mainland. The currents are now 
semi-diurnal. Near Cape Sirik the flood runs for four hours and the ebb for eight 
hours, so that a considerable diurnal component exists, but not sufficient to prepon¬ 
derate over the semi-diurnal motion. The velocities here are from two to three knots. 
At Bruni the observations are very much interfered with by shoals and narrows, but 
in the offing the currents seem to be about two to three knots. About Tega, however, 
among shoals the velocities recorded are only T3 and 0'8 knots. The contours of the 
sea floor run roughly parallel to the coast, so that these currents may persist for some 
distance out to sea. Off the north end of Borneo the sea rapidly deepens, and in 
accordance with this there is scarcely any tidal current at Ulugan Bay, in Palawan. 
On the Asiatic side the tide is diurnal at Camran and Tourane, but the currents are 
weak. 
A few shoals and islands in the middle of the sea have been made the localities of 
observations. At Bifleman Bank and Spratly Island there is only one tide in the day, 
and at the neighbouring island of Amboyna it is said that near neaps the stream 
reaches 1'4 knots. It is therefore clear that the semi-diurnal current of the Borneo 
coast does not extend half way across the sea, and its true extent is very doubtful. 
In the Gulf of Tongking also the currents appear to be diurnal. Thus in the whole 
of the South China Sea and its extensions there seems to be little semi-diurnal tide 
and little contribution to the secular acceleration of the moon, though there is a 
dissipation of the energy of the diurnal tide that may have a notable secular effect on 
the obliquity of the ecliptic. 
2. The Yellow Sea. 
This is a gulf about the size of Ireland, lying between Korea and the coast of 
China, and extending about as far south as the mouth of the Yang-tse-Kiang. It 
becomes very narrow where the Shan-tung peninsula projects into it, and north of 
this it forms the Gulfs of Pe-Chili and Liau-tung. Most of it is shallow, the depths 
in the main part of it being mostly about 30 fathoms, and those in the northern part 
about 15 fathoms. Around the shore the water is shallower, and in many places 
there are crowds of shoals. The data are obtained from the ‘ China Sea Pilot/ vol. 5. 
The tidal phenomena are extremely complex. At the south end of the peninsula 
of Korea high water (full and change) is at about 11 h., Greenwich time. As we 
advance up the Korean coast it occurs later and later, being practically 12 hours 
