[pawson] METHODS OF INVESTIGATION OF TIDES & CURRENTS 9 
summarized in a paper contributed to the Royal Society of Canada (10). 
The effects are classed under the headings of Weak Currents, Constant 
Currents, and Strong Tidal Streams. The importance of a comparison 
of the under-current with the surface direction, as an indication of 
disturbance, is also explained. 
Little has yet been done by this Survey in the study of the influ- 
ence of wind and barometer in modifying the height of the tide. There 
is more published information on this subject, however, than on the 
effect of the wind in increasing or retarding the horizontal movement 
of the water and disturbing the normal conditions which would other- 
wise prevail. Some attention has been given to the secondary undu- 
lations shown by the tide curves, which are apparently related to 
meteorological conditions; and two papers in which examples are given, 
and some general characteristics in their mode of occurrence, have been 
contributed to the Royal Society (11). 
It may be well to draw attention, however, to the excellent oppor- 
tunity for the study of this whole subject which the St. Lawrence 
estuary affords. It is one of the largest estuaries in the world, with 
a tide of only four or five feet at its mouth, increasing to nearly 20 
feet at its head. A large amount of material is now available for the 
purpose, as this Survey has now accumulated record from registering 
tide gauges continuously during 14 years; and with this, there are 
meteorological observations from ten stations in the area extending 
from Quebec to Newfoundland, and daily weather charts, which have 
been fyled from the outset for comparison with the tidal observations 
themselves. 
TipAL INVESTIGATIONS. 
The general method adopted for the investigation of the tides, 
both on the Atlantic and Pacific coasts, has been the same in its general 
features. Principal tide stations were established at stategic points 
to serve as reference stations for the harbours in their vicinity. Owing 
to the clear field which this Survey had before it at the beginning, the 
choice of principal stations was unhampered; but as practically nothing 
was known regarding the character of the tides, it was necessary to 
feel the way carefully to avoid the undue multiplication of principal 
stations and to extend as far as possible the region referred to each of 
them. 
For a satisfactory reference station the position chosen had to be 
free from local influences. It thus happens that an important harbour 
may be entirely unsuitable as a port of reference, because of its situ- 
ation at the mouth of a river or within an inlet. On the other hand, 
some isolated island or lighthouse, of no importance whatever on its 
