On the Tides of the Western Coast of the United States. 9 
Difference in height of highest tide and lowest tide in day: 
average, 5 feet 11 inches; greatest, 7 feet 7 inches. 
ep the moon’s declination is north, the highest of the two 
high tides of the day is the one which occurs about twelve hours 
after upper culmination. ' 
have given elsewhere, for the use of navigators, a set of rules 
founded on these observations, and containing no technical term 
unfamiliar to them. 
Notes on the Tides at San Francisco, California. 
Besides the ordinary changes in the time and height of the tides 
known to all navigators, it is important to note the following, 
generally applicable to the Western coast, and particularly to San 
rancisco bay. They relate to peculiarities in the tides which 
occur on the same day, the necessity for knowing which is shown 
by the fact that a rock having three feet and a half of water upon 
it at low tide, may, at the succeeding low waicr, on the same day, 
be awash : 
1. The tides at Rincon Point, in San Francisco bay, consist 
generally of a large and small tide on the same day; so that of 
two successive high waters in the twenty-four hours one is much 
higher than the other, and of two successive low waters one is 
much lower than the other. 
- The difference in height of two successive tides (either high 
or low waters) varies with the moon’s declination. When the 
declination is nothing, the difference is nothing, or very small. 
hen the declination is greatest, whether south or north, the dif- 
ference js greatest. When the moon’s declination is nearly 
nothing, the intervals between two successive high or two succes- 
Sive low waters are nearly twelve hours, and twenty-five minutes, 
and differ most from this when the moon’s declination is greatest. 
- The inequalities in the heights of successive low waters 
are more considerable than those of successive high waters ; 
while, on the contrary, the inequalities in the times of high water 
are more marked than those of low. 
_* ‘The average difference between the heights of two succes- 
Sive high waters is one foot three inches ; and of two successive 
». T’he average variation from twelve hours and twenty-five 
* 
Waters fifty-three minutes. The average variations of the same 
interval when the moon is farthest from the equator are, Tespect- 
ively, two hours and one hour and a quarter. 
Szaus, Vol. XXI, No, 61.—Jan., 1856. 
’ 
