LXXII ROYAL SOCIETY OF CANADA 



rents of the estuary to be readily and accurately known from the tide 

 tables. 



Northumberland Strait. — In the present report of progress all the 

 information yet obtained is summarized with regard to the tide and 

 current in Northumberland Strait, and its relation to Cabot Strait, 

 where the Gulf of St. Lawrence opens to the ocean. The levels of 

 datum planes, heights of extreme tide, and the effects of wind dis- 

 turbance, have also been carefully and fully worked out. These are 

 of primary importance with relation to^ works of construction in the 

 harbours of the Strait, «as well as for uniform reference levels in any 

 future observations. 



St. Eaul Island is the principal station to which the tides on the 

 south-west side of the Gulf of St. La^wrence and in the region of 

 Northumberland Strait are referred; and comparative observations 

 were taken on the two sides of Cabot Strait, to see whether a sufficiently 

 constant relation could be established with St. Paul Island to enable 

 either of these localities to be used to replace it as a reference station 

 for the regions above referred to. The extreme exposure of St. Paul 

 Island makes the gauge usually liable to accident; and once already 

 it has been carried away, and twice afterwards it was partially wrecked 

 by winter storms. 



The endeavour was first made to obtain comparisons with Sydney 

 harbour and Port aux Basques on the two sides. The tide at Sydney 

 has so unusual a character, with large secondary undulations, which 

 are often one-third the height of the main tide, that it was quite 

 unsuitable for comparison with St. Paul Island. After one complete 

 month was secured at Sydney, the gauge was removed to Neil Harbour, 

 a point on the Atlantic side of Cape Breton Island, as near to its nor- 

 thern extremity as practicable. At Port aux Basques the unusual 

 result was found that the two tides of the day are alternately earlier 

 and later than at St. Paul Island when the moon's declination is high. 

 Accordingly, these observations brought out in the clearest light the 

 pre-eminent advantage of St. Paul Island over the other localities in 

 Cabot Strait, as a station to command the whole region under con- 

 sideration. This advantage must depend largely upon its being situ- 

 ated in deep water; the lOO-fathom line being within three miles of the 

 eastern shore of the island, on which the tide gauge is situated. It 

 emphasizes also the importance of choosing strategic points as principal 

 stations, whatever the exposure and the difficulties in maintenance may 

 be, in preference to sheltered harbours where the tide itself is more 

 irregular, owing to the shallower water or greater local interference. 



Current in N ortliumberland Strait. — Observations were taken on 

 the north shore of Pictou Island, which is centrally situated in the 



