124 THE ROYAL SOCIETY OF CANADA 
is not constant; but a variation is found to occur during the course of 
the month. Broadly speaking, this is no doubt due to the variation 
in amplitude from springs to neaps which affects the rate of translation. 
But as a hydraulic problem it is complex; because we are not dealing 
with a channel of uniform width, but with one in which the area is 
restricted at low water by the exposure of foreshore and bars. If the 
amplitude were constant, this variation in the hydraulic mean depth 
would no doubt be constant also in its effect; but when this depth is 
a pronounced function of the varying range, so much complication 
results that the ordinary formula for wave transmission is no longer 
applicable. 
The following examples show a distinct variation in the time- 
interval from springs to neaps, and that this variation is also greater 
for low water than for high water. The differences are in absolute time 
as before. 
Estuaries. For H.W. For L.W. 
Father Point to Quebec. Distance 180 miles. Spring 
range, 14 feet at Father Point to 18 feet at Quebec. . 
Time interval about Spring tides........... 4h. 22m. 5h. 38m. 
x =. JNeapitides FAT UE 4h. 18m. 5h. 18m. 
Port Essington, B.C., at 12 miles within the mouth of the 
Skeena river. Compared with Port Simpson on the 
open Pacific. Spring range 21 feet.............. 
Tide later than Port Simpson, at the Sa Oh. 34m. Oh. 59m. 
< at the Neaps...| Oh. 27m. | Oh. 32m. 
An endeavour was made to reduce the variation in the time- 
interval on the St. Lawrence to a function of the actual height at 
Quebec. The variation is much more pronounced for low water than 
for high water; and the total variation is much greater than the above 
averages indicate. An excellent series of observations was available, 
obtained during two complete years summer and winter, and thus 
affording 1,280 time-intervals between the two places. But it was 
not found possible to obtain a satisfactory relation between time- 
interval and height. The anomalous result may be due, in part, to 
the situation of Quebec; as it must be regarded as on the river above 
the true head of the estuary, which is properly at the lower end of 
Orleans island where the tide has its greatest range. The height is 
thus involved with water slope on the last 30 miles of the distance. An 
astronomical method was therefore preferred for calculation purposes, 
allowance for variation being made in the periods of two of the lunar 
months. The total variation in the time-interval thus allowed for, was 
