258 
DE. HAEOLD JEFFEEYS ON TIDAL FEICTION IN SHALLOW SEAS. 
order h (g/ D)*; in a simple wave in a uniform channel it is exactly this. Taking the 
depth to be 90,000 cm., this makes the maximum velocity 19 cm./sec., or rather more 
than a third of a knot. Accordingly the currents with velocities of a knot or more 
must be confined to narrow coastal strips, and the dissipation is therefore small. 
The only other partially enclosed regions around Africa are the Gulf of Aden and 
the Red Sea. The former is deep in the middle with narrow strips of shallow water 
on the margins, like the Mozambique Channel, and therefore the dissipation is small. 
The Red Sea is shallower, but can have no important currents, since the inlet at Aden 
is so narrow. The Mediterranean has already been dealt with. Thus the dissipation 
around the coasts of Africa is negligible. 
North American Waters. 
There are many partially enclosed bodies of water around North America, the chief 
of which are the Gulfs of Mexico and California, the Bay of Fundy, the Gulf of 
St. Lawrence, and the numerous straits and bays of the North-west Passage. Of 
these the Gulf of Mexico may be ruled out at once, for it is very deep and a large 
fraction of its entrance is blocked by Cuba. The Gulf of California is still deeper ; and 
therefore the currents in these cannot be notable except in restricted localities. 
1. The Bay of Fundy. 
This bay requires to be considered separately in spite of its small size, for it is 
famous for possessing the largest tides in the world. It is fairly shallow, and the 
tides are much magnified in height by the diminution in both depth and width 
towards the head of the Bay. The currents are apparently not so great as would be 
expected from the height of the tides. The entrance is through the Grand Manan 
Channel, named after an island in it. The average current in the channel reaches 
about 1'8 knots, and that near St. John, half-way up the bay, reaches 17 knots. The 
area of the bay is 12,000 sq. km., so that the average dissipation for a maximum 
velocity of 1'8 knots all over would be 77 x 10 16 ergs per second. It is likely that the 
currents farther up the bay are stronger, so that this must be regarded as a lower 
limit. 
An alternative estimate may be obtained from the inflow of energy. The rise of 
the tide in Grand Manan Channel is at most places about 20 or 22 feet at springs ) 
above low water ordinary springs. The amplitude is therefore about 320 cm. The 
current has an amplitude of 1‘8 knots, and the depth of the channel is about 9000 cm. 
The average time of the turn of the current at three places near the south side 
of the channel (those numbered 14, 16 and 17, in the ‘ Nova Scotia and Bay of Fundy 
Pilot,’ page 22) is 35 minutes after high water at St. John. This high water at full 
and change occurs at 11 h. 21m., while at l’Etang, on the north side of the channel, 
