[DAWSON] THE TURN OF TIDAL STREAMS 75 
of correlating slack water directly with the time of high or low water, a 
more constant difference may be obtained with reference to the mid- 
time between high and low water, which may be termed the moment 
of half tide. (3) The time of maximum current, or the mid-time be- 
tween slacks, may be used, instead of the time of slack water, in 
either of the ways above indicated. (4) These methods may further 
be combined with a distinction of the two slacks, or of flood and ebb; 
to refer them respectively to two tide stations in the oceanic and the 
inland directions, as may be found best. The method to be finally 
adopted, is the one which gives the most constant time-relations. 
These various methods were thoroughly tried in dealing with the 
entrance to the Bras d’Or lakes; which consist of two expanses, the 
outer communicating with the ocean. The rise of the tide in the open 
is 3 to 5 feet, but the lakes have not time to fill up in the tidal period, 
and their variation in level is only about 6 inches. The methods as 
applied to this case, would well explain the matter. The best results, 
for the outer entrance as well as for the Narrows connecting the two 
expanses, was found by correlating the time of mid-flood and mid-ebb 
with high water and low water at different tidal stations in the op- 
posite directions. Information in this form is quite satisfactory to 
the navigator. 
Where the current is violent, and navigation is only possible 
near slack water, the methods available are much restricted. Such 
conditions are presented by Slingsby channel, opening by one narrow 
entrance into a series of six inlets and sounds branching off each other. 
This is opposite the northern end of Vancouver island and is developing 
as an important lumbering region. The rise of the tide in the open 
is 12 to 15 feet; while within the inlets it is only 6 to 8 feet at its greatest. 
The tide pours through in a torrent; and any attempt to tow lumber 
out, except at slack water, results in wreckage. 
There was no constant relation between slack water and the time 
of the local tide; but for high-water slack, a constant time-difference 
was found with the tide of the open Pacific, on the outside of Vancouver 
island. For low-water slack, the time-intervals varied widely. It 
was found that the trouble really arose from the inequality in the 
time-intervals between successive slacks; these intervals becoming 
10 hours and 15 hours alternately, when the moon is near its maximum 
declination. An exhaustive investigation was therefore undertaken 
to find some tide station where such an alternation was presented by 
the tide itself, in the hope that a constant difference would result. 
At two tide stations, in northern and southern British Columbia, 
the alternation in the intervals between successive high waters is 
greater and less respectively, than the intervals required. The values, 
