APPENDIX C LXXIII 



eastern end of this strait. It was found that the variation in the 

 difference of time between the turn of the current and the tide is 

 large; as the turn may take place as much as two hours before high 

 water or after low water. The greater part of the variation follows 

 the change in the moon's declination; as this has been found from 

 the first to be the ruling element in this region. This is very con- 

 fusing to the mariner, as the turn of the current in relation to the 

 tide is out of accord with the moon's phases, and has thus no fixed 

 relation to the spring and neap tides. The greatest apparent irregu- 

 larity is when the moon's declination is at its maxinium; and this 

 occurs sometimes at the spring tides and sometimes at the neaps. The 

 ordinary navigator takes refuge in the conclusion that the currents 

 are chiefly influenced by the wind. But these observations show that 

 the apparent irregularities can be reduced to definite laws, which 

 although complex, are strictly astronomical in character. 



Further observations. — Five summer tidal stations were erected last 

 season with the object of obtaining tidal data as a basis for the inves- 

 tigation of the current at the entrance to the Bay of Fundy, and in 

 the bays on the south coast of Newfoundland. One of these was 

 placed at Trepassey Bay, within sixteen miles of Cape Race, the ex- 

 treme south-eastern angle of Newfoundland. 



Levels and Datum .planes. — This survey, as a branch of the Depart- 

 ment of Marine, has for its primary object the determination of the 

 time-relations of the tide, and the turn of tidal currents, for the infor- 

 mation of mariners. The determination of levels is thus quite collateral 

 to the object which the department has in view, but it was very evi- 

 dent that a large amoimt of important information could be secured by 

 taking more complete levels, and by establishing bench-marks at all 

 tidal stations at which recording instruments were placed, even for a 

 few months. The additional work involved was therefore undertaken 

 from the outset. Eventually, as the observations are continued, the 

 value of mean sea level, extreme tide levels, and other factors of 

 importance, are determined with reference to this bench-mark. Such 

 factors are of the highest value in city drainage works and harbour 

 improvements. In certain rare instances, bench marks have been 

 established by the Admiralty, which define the lower water datum of 

 the charts. These are always taken advantage of, where they exist. 

 When the height of the tide is referred to this datum level, it shows 

 the depth available in addition to the chart soundings. 



A paper has been contributed to the Canadian Society of Civil 

 "Engineers, by Dr. W. Bell Dawson, entitled " Tide Levels and Datum 

 Planes in Eastern Canada," in which values for mean sea level are 

 given for Halifax, St. John, and Quebec, based upon several years of 



