124 
SHIDY. 
pendent upon this region or “ oscillating area/’ would be 0.9 
+ 6 = 6.9, or about 7 hours for the west end, and 0.9 + 12 
= 12.9, or about 13 hours, which, since the period of the force 
is 12 hours, is equivalent to 1 hour for the east end. The 
former value agrees fairly well with the observed values for 
that portion of Brazil, and so might seem to help explain the 
controlling tide there. But other requirements for an “ os¬ 
cillating area ” prevent this from being the true explanation. 
It would be interesting to describe in detail the seven sys¬ 
tems which have been mentioned as causing the semidiurnal 
tides in most portions of the world, but the difficulties of pre¬ 
senting them in a satisfactory way in a brief address renders 
it impracticable to attempt it at present. 
Passing on to the localities forming fractional areas having 
dependent stationary waves, some of the best known are the 
following bodies of water: The English Channel, the Irish 
Sea, the Gulf of St. Lawrence, the Gulf of Maine, Long Island 
Sound, Bahia Grande (Patagonia), Chacao Gulf (Chile), the 
Gulf of Georgia (British Columbia), and several of the so- 
called Alaskan “ canals,” the Bay of Bengal, and the Gulf of 
Suez. 
The time alloted for this paper is too short to treat of all 
the above interesting tidal bodies of water, and I shall close 
with a brief reference to the tides of the Gulf of Suez and the 
Gulf of Maine. 
The Gulf of Suez is the western arm of the northern end of 
the Red Sea. It is about 160 sea miles long, perhaps 15 miles 
broad, and has an average depth of about 20 or 25 fathoms. At 
about one-fourth of the way from its southern entrance is the 
small village of Tor, which is interesting to students of tidal 
phenomena because it is one of the comparatively few places 
along the sea coasts of the world at which there is very little 
or no tide—that is, no perceptible periodic vertical rise and 
fall of the water—while at the same time the tidal currents 
or horizontal movements of the water are quite marked. A 
little way on either side of Tor, or, more accurately, of Tor 
Bank, there is a sensible tide, which increases in range quite 
