APPFNDIX — REPORT ON THE SUMMER CAMP AT QUACO. 69 



Tidal Phenomena at Quaco. 



By Prof. A. Wilmer Ddff. 



The point that the writer was chiefly interested in was the occur- 

 rence of those somewhat puzzling phenomena called " secondary 

 undulations." Anyone who examines the record of the Kelvin Tidal 

 Gauge at St. John will find that it gives a wave-shaped curve, the 

 heights of which correspond with the time of high water and the 

 hollows with the time of low water ; but, in addition, he will discover 

 that on this main curve there are smaller indentations, indicating 

 minor risings and fallings of water level, the whole time from greatest 

 of these minor undulations to the next greatest rise being, on an average, 

 about forty minutes. These small and comparatively rapid oscillations 

 of level are the so-called " secondary undulations," and the time of 

 forty minutes required for them to complete their cycle of changes of 

 level is called their period. 



The author had already shown* that these secondary undulations 

 could be explained as due to a long, slow oscillation of the whole body 

 of water between the New Brunswick and the Nova Scotia coast, the 

 vibrations being similar to these that are set up in a wash-basin full 

 of water when it is disturbed. It became, then, an interesting point 

 to determine whether the rest of the body of water in the bay partook 

 of this same general motion, and whether the period was the same as 

 at St. John. The author fully expected that it would be. 



With this in view, the tide gauge described in a former communica- 

 tion f to the Society was used at Quaco. On three different days the 

 gauge gave clear records of " secondary undulations ;" but, contrary 

 to his expectations, the period in all cases was 12^ minutes. This was 

 a somewhat puzzling result, until it occurred to the writer to examine 

 the chart of the bay off the New Brunswick coast in the neighborhood 

 of Quaco, when he found that the presence of a reef called the Quaco 

 Ledges, and the two headlands that project into the bay above and 

 below Quaco, respectively, marked out a smaller bay (open, it is true, 

 to the east), in which the water would naturally oscillate in a period 

 of its own, determined by its own dimensions. From the smallness of 

 its dimensions these oscillations might be expected to be much quicker 

 than those across the bay at St. John, although the irregularity in 

 shape of this small bay precludes any attempt to calculate mathemati- 

 cally what the period of the oscillations of the water in it would be. 



♦See American Journal of Science, Vol. Ill, No. 17, 1897. 

 tSee Bulletin XV of the Natural History Society of N. B., 1897. 



