SECTION III., 1895. [25] Traxs. R.S. C. 
III Note on Secondary Undulations recorded by self-registering Tide 
Gauges; and on Exceptional Tides in relation to Wind and Barometer. 
By W. Beri Dawson, MA.E., Assoc. M. Insv. C.E. 
(Presented by Dr. Johnson, May 15, 1895.) 
In carrying on the Tidal Survey for the Department of Marine, the 
writer would desire to draw attention to the secondary undulations which 
are met with, as a matter of scientific interest. These undulations are 
registered by more than one of the recording tide guages now in opera- 
tion. They stand in much the same relation to the main tidal wave as a 
higher octave would to a low musical note, when their undulations are 
recorded graphically. 
They are especially noticeable at St. John, N.B., where the amph- 
tude of the tide itself magnifies these undulations also. The tide has there 
a range of some 28 feet ; and the secondary undulations, which are chiefly 
evident at high and low water, have an amplitude which is sometimes 
‘over one foot, and a period of about 40 minutes. These minor undula- 
tions often continue for a week at a time ; or even longer. An example 
is given on drawing No. 1; which shows portions of the actual trace 
from the tide gauge, and a projection of the secondary undulations from 
which the main tidal curve is eliminated. 
Such undulations have been observed before at Halifax during the 
tidal observations taken there in 1863; and they are described in Short 
land’s “ Nautical Surveying,” as having a period which varied from 5 to 
25 minutes, and a range which rarely exceeded four inches. This cor- 
responds with the lower amplitude of the tide at Halifax, Similar 
undulations have also been observed at Malta. It does not appear that 
uny satisfactory explanation has yet been given to account for them. 
The record of the Bay of Fundy tides as obtained at St. John, would 
probably furnish as good an opportunity as could be found anywhere to 
investigate this phenomenon, if there were any one who could afford time 
to do so as a matter of scientific interest. For the main purpose of tidal 
computation, these undulations are merely treated as an irregularity in 
the tide curve itself which has to be eliminated in its reduction? 
Another matter of interest is the effect of the wind and barometer 
on the tides of the lower St. Lawrence. The three recording gauges at 
Anticosti, Father Point, and Quebec, are now giving full information 
regarding the progress of the tide; and the data are completed by the 
regular meteorological observations. The range of the tide at Anticosti 
is only about four feet ; at Father Point twelve to sixteen feet ; and at 
