Secondary Undulations of Oceanic r Tides. 125 
apparent beat of semi-diurnal tides. The period of the cha- 
racteristic component, which forms a beat with the usual 
semi-diurnal tide, is about I0 h, 9, as estimated from the 
rectified curve. It is probably to be attributed to the standing- 
oscillation of the St. Vincent Gulf. Taking the month-line 
from Troubridge Point to Cape Jevis, and the end of the gulf 
at Wakefield, we obtain £=140 km., and the estimated mean 
depth is 21*5 m. Hence T = 10 h, 8, which coincides very well 
with the observed period. 
(v.) Port PlaJlip. Australia. — Mareogram of Williamstown 
given in the above quoted Report shows some irregularities of 
tide, which suggests the existence of very long undulations pe- 
culiar to the bay. The curve was rectified and a period of 8 h, 3 
was detected. Xow the period of seiches in this nearly enclosed 
basin can by no means become so long as 8 h , unless the mean 
depth of the Port be less than one metre. This period is 
probably due to the undulation of the whole basin with its 
narrow neck communicating with the open sea. For the calcu- 
lation of the period corresponding to this mode, the necessary 
data were estimated from the chart given in Harris's Report : 
S = 13-7xl0 8 m. 2 , / = 2-95km., b = ±08 km., h = 18-4 m. and 
L = 200 km. The period calculated from these data is 8 h# 39 
by formula (5). § 4, which almost coincides with the observed 
period. 
Besides the above enumerated examples, there are many 
bays, or straits, the forms of which seem favourable for their 
own standing oscillation of long periods, and in which the 
ranges of tides are comparatively large. The periods of these 
oscillations were estimated as follows : — 
Bay or Strait. 
T in hours. 
Adriatic Sea 
15 
7 
15 and 28 
7 
11 
5 
7 
Mozambique Channel 
Bristol Bay. Alaska 
Hecate Strait, British Columbia 
Hudson Strait, Canada 
Bristol Channel, England 
, Gulf of St. Malo, France 
As we have no tidal records of these bays and channels at 
hand, discussion must be omitted. We conclude this section 
WZbi 
