APPENDIX D LXXIX 



Character of the Pacific tide. — In all parts of the world, the tides 

 are found to accord with the varying movements and distances of the 

 moon and the sun. In the jSTorth Atlantic, where they w^ere first studied, 

 it happens that they are chiefly inflLienced by the moon's phases. It was 

 thus supposed that the primary characteristic of all tides was a marked 

 alternation in height from springs to neaps in the period of the synodic 

 month. 



The tide of the Pacific, however, can best be described as a declina- 

 tion-tide. Its leading feature is a pronounced diurnal inequality m 

 time and height, which accords witli the declination of the moon; and 

 t]iis is also subject to an annual variation with the change in the declina- 

 tion of the sun. The period in which the diurnal inequality recurs is 

 the tropical or declination-month, of 27.2 days; which is shorter than 

 the sj^nodic month and gradually falls bac'.c through its period in suc- 

 cessive months. As the solar influence is unusually large in the Pacific 

 relatively to the lunar; the annual variation is the more accentuated. 



On the o^^en coast of the Pacific, the tide curve is still fairly regu- 

 lar, though showing the diurnal inequality strongly. But in the 

 Strait of Fuca and the region of the Strait of Georgia, which makes up 

 half the coast line in British Columbia and where all the more im- 

 portant harbours are situated, the appearance of the tide curve is 

 anom lous. The high waters are nearly at the same level; and the 

 range depends on the amount of fall to low water, which may be almost 

 inappreciable or very pronounced. During the greater part of the day, 

 there may thus be a long stand or only a slight fluctuation near the 

 high-water level; with a sharp and short drop to the lower low water 

 which occurs once in the day. This type only changes to a fairly sjm- 

 metrical curve when the moon is on the equator near the time of the 

 equino!xes. 



The spring and neap tides are thus reduced to a secondaiy featiiipe 

 which is usually obscured by the stronger characteristics of the tide. 

 The Estai )lish:nent. which is so well marked in the Atlantic, is here 

 almost illusor}^; unless it is strictly reduced to equinoxial and equaitorial 

 fc'jnditions, in a:co dance with thi defiiition u;el in France, It may 

 still be convenient to speak of spring and neap tides, if they are under- 

 stood to mean the two maxima and the two minima in range or in level 

 which always occur in the period of the lunar month. But the two 

 highest and the t^\-o lowest points on the tide curve for the month, may 

 be as much as five days before or after the full or new moon, as these 

 extremes are so largely occasioned by the diurnal inequality. 





c 





■i^^^^'v 



