DR. HAROLD JEFFREYS ON TIDAL FRICTION IN SHALLOW SEAS. 
253 
entrance, when the current is flowing strongest, the dissipation in a strip a centimetre 
wide across it is 0 ' 002 p\Jdy, and if the above distribution of velocity is correct this 
is l' 2 xlO u ergs per second. Farther north the velocity is not so great; in fact, 
around the Shan-tung promontory it does not exceed one knot, and at the islands in 
Korea Bay opposite it is usually about two knots. Further, the width is here less 
than 300 km., so that on this account also the dissipation for a given velocity must be 
less ; the amount in a strip a centimetre wide running east and west is therefore 
probably not more than oue-sixteenth of that in a similar strip near the entrance. 
Even south of the narrow part off Shan-tung the currents appear to be slower than 
near the entrance ; for about half the distance the velocity is about two knots, rising 
again to 3f knots at the Sir James Hall group, in the narrow region. If a proportional 
reduction takes place at all other distances from land, we must suppose that the above 
estimate of the dissipation per unit length is correct for the first 200 km., that the 
amount for the next 230 km. is an eighth of this, and that for the remaining 220 km., 
corresponding to Korea Bay, is a sixteenth. The Gulfs of Pe-Chili and Liau-tung may 
be ignored. The total dissipation, if the maximum velocity at every place occurred 
at the same time, would therefore be (2 x 10 7 + -g- x 2'3 x 10 7 + yg- x 2‘2 x 10 7 ) l'2xlO u 
ergs per second, or 2 ' 8 xl 0 18 ergs per second. The average for each place is 
4/3 7 r of the maximum there, so that the average tor the whole sea is 4 / 37 T of this 
maximum, or l' 2 xl 0 18 ergs per second, which agrees with the previous estimate 
much more closely than the data would have led us to expect. 
3. The Sea of Japan. 
The Sea of Japan is an oval basin bounded on the eastern side by Japan and 
Sakhalin. It seems clear that the dissipation is small, for both the tide height and 
the current are small. Even in the comparatively narrow and shallow Korea Strait, 
through which the tide enters at the south end, the current only attains a speed of 
1 or 2 knots ; and when this opens into the sea the width suddenly increases to 
900 km. and the depth to 400 fathoms. The currents in most of the sea must there¬ 
fore be insignificant. They are appreciable at the gaps between the Japanese islands 
and in part of the narrow Gulf of Tartary, but the area affected is small and the 
currents only moderate (l to 3 knots at most) so that the dissipation is small. 
4. The Sea of Okhotsk. 
In its essential features this resembles the Sea of Japan. The only shallow parts 
of it are narrow strips around the coast, while the tide enters through the shallow 
water of the straits between the Kurile Islands. As the tide in the sea depends on 
the supply of water to maintain it, the restriction on it imposed by the shallowness of 
the entrances causes the currents to be small. In the Gulfs of Ghijinskand Penjinsk, 
in the north-east corner, the depth diminishes considerably, and the currents increase 
