s 6 ROYAL SOCIETY OF CANADA 



The reason of this is that the tide in Cabot strait is affected by a large 

 diurnal inequality. The two tides of the same day have thus a long 

 interval and a short interval of time between them ; and their ranges are 

 also very different in amount. These inequalities attain a maximum value 

 when the moon's declination is greatest north or south of the equator > 

 and they disappear at the nodes. Hence the period of the variation is 

 the draconitic month, which is reckoned from the ascending node of the 

 moon to its next ascending node. Its mean length is 27** 5*" 5™ 36' , or 

 2-32 days shorter than the synodic month. Its commencing point thus 

 retrogrades through the synodic month in a period of less than thirteen 

 lunar months. 



This inequality, which is so marked in Cabot strait, appears to be 

 occasioned by the over-running of the tide by a tidal undulation from 

 some other direction. It disappears almost entirely from the tide after 

 it enters the mouth of the St. Lawrence ; and at Father Point and Quebec 

 it is seldom appreciable. It was known, however, that the tides at 

 Pictou and Charlottetown in ISTorthumberland strait, were affected by 

 diurnal inequality ; but the reason of this was not understood. It has 

 been customary in the past to refer the tide at ports within the Gulf, to 

 some port of reference on the Atlantic coast ; but this occasions an error 

 of nearly 1^ hours, early or late, in the time of high water ; which is 

 chiefly due to the inequality referred to. 



These conditions made it necessary to obtain simultaneous tidal com- 

 parisons at a series of points extending from Cabot strait to Gaspé, in 

 order to trace out the progress of the tide, and to ascertain how far these 

 irregularities are felt. The results obtained at these jjoints could also be 

 compared with any of the principal tidal stations ; and the extent of the 

 region which can be referred to each of them as to a port of reference, 

 could thus be decided, which is the important question from a practical 

 point of view. 



A series of secondary tidal stations was accordingly established in 

 the season of 1896, extending from Chaleurs bay along the southwestern 

 side of the Gulf, through Northumberland strait, and around Prince 

 Edward Island. In this region the principal harbours had the first claim, 

 and consideration had also to be given to the relative importance of places 

 from a tidal point of view, so as best to obtain tidal differences for inter- 

 mediate points. The choice of the following stations was accordingly 

 made : — Carleton, which is as near the head of Chaleurs bay as possible, 

 while avoiding the local influence of the Eestigouche river ; Lower 

 Neguac, near the mouth of Miramichi bay, where the Gulf shore is 

 furthest distant from the entrance at Cabot strait ; Charlottetown, where 

 the tide in Xorthumberland strait is latest in time, and has also the 

 greatest range ; Pictou, in line with the open channel between Prince 

 Edward Island and Cape Breton Island, up which the tides pass ; and 



