Shown hy Recording Tide-gauges. 137 



Yet, if we consider the Bay of Fundy, exactly the opposite is 

 true. Yarmouth is at the mouth of the bay and there the 

 oscillations sometimes reach 5 ft.; St. John is half way up the 

 bay and there the oscillations never exceed 2 ft. ; while at the 

 head of the bay, where, as is well known, the rise of the tide is 

 enormous, Hopewell Cape, Parrsboro and Windsor show no 

 secondary undulations. Again Carleton, Q., is at the head of 

 Chaleurs Bay, but the undulations there are particularly slight. 

 At Cape Tormentine, which is in the narrowest part of 

 .Northumberland Strait, there are no secondary undulations 

 and the same is true of Charlottetown, while they are very 

 frequent at Pictou and Souris near the entrance of the Strait. 



On the other hand, it is to be noted that, according to the 

 seiche theory, secondary undulations would not be expected in 

 shallow basins such as those at the head of the Bay of Fundy ; 

 since, if oscillations of the whole body of water were started, 

 they would rapidly die away in such shallow water. 



On the whole, the theory of " atmospheric billows," while 

 ingenious and attractive, seems to me wholly untenable as 

 regards the period of undulation and very improbable as 

 regards the origin of such undulations (I am not of course 

 referring to the agency of atmospheric disturbances in general), 

 whereas the " seiche " theory offers the only tenable explana- 

 tion hitherto advanced, but leaves points still unexplained. 



A general view of the vibrations of large bodies of water. 



It may be well at this stage to make explicit a general view 

 implied in the preceding discussion. It seems probable that a 

 large body of water, such as the Gulf of St. Lawrence or the 

 Bay of Fundy, when disturbed breaks up into smaller areas of 

 oscillation, determined by irregularities in the level of the bed ; 

 these minor basins oscillate to a considerable extent independ- 

 ently, at rates determined by their respective dimensions and 

 the depth to which they are filled, the oscillations being at 

 times in the fundamental mode, but at other times in some 

 higher mode, but with a tendency to the establishment of some 

 particular mede that gives a characteristic period to the basin. 

 Frequently, owing to the co-existence of different modes of 

 vibration, and owing to invasions from the vibrations of neigh- 

 boring basins, the vibrations of each minor basin become more 

 or less irregular ; but such irregularities are comparatively 

 rare in a part of the main basin with only slight irregularities 

 of bottom and bounded on opposite sides by nearly parallel 

 coasts (as is the case of the Bay of Fundy at St. John, where 

 the records show a more constant period of undulation than at 

 any other tidal station on the eastern coast of Canada). 



