Ephemeris of the Planets for the First, Tenth and Twentieth days of Month. [Calculated for the Meridian of San Francisco.]

Ephemeris of the Planets for the First, Tenth and Twentieth days of Month.

[Calculated for the Meridian of San Francisco.]

Ephemeris of the Planets for the First, Tenth and Twentieth days of Month. [Calculated for the Meridian of San Francisco.]

II. LATITUDE AND LONGITUDE.

LATITUDE AND LONGITUDE

Of the Principal Points on the Pacific Coast, determined by George Davidson, U. S. Coast Survey.

NOTE.-Primary astronomical stations in SMALL CAPITALS; the series of observations at these sta

tions extend through not less than two or three lunations. Positions determined by trigonometrical connection with astronomical stations, in Italics. All other determinations by chronometric connecThe localities of the astronomical stations and observatories can be more definitely determined by tion with primary astronomical stations for longitude, and independent observations for latitude. reference to the published maps, etc.

III.-TIDES AT SAN FRANCISCO, CAL.

[By Prof. A. D. Bache, Superintendent U. S. Coast Survey.]

Besides the ordinary changes in the time and hight of the tides known to all navigators, it is important to note the following, generally applicable to the Western Coast, and particularly to San Francisco 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 and a half feet of water upon it at low tide, may, on the same day, at the succeeding low water, 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 the two successive low waters, one is much lower than the other.

2. The difference in hight 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. When the declination is greatest, whether North or South, the difference is greatest. When the moon's declination is nearly nothing, the intervals between two successive high, or two successive low waters, are nearly twelve hours, and differ most from this when the moon's declination is greatest.

3. The inequalities in the hights 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.

4. The average difference between the hights of two successive high waters is one foot four and a half inches, and of two successive low waters two feet four inches. The average difference of these same hights, when the moon's declination is greatest, is for the successive high waters two feet, and for the low waters three feet six inches.

5. The average variation from twelve hours, in the interval between two successive high waters, is three-quarters of an hour, and between two successive low waters, half an hour. The average variations of the same intervals when the moon is furthest from the Equator, are, respectively, one hour, and three-quarters of an hour.

6. When the moon's declination is North, the higher of the two high tides of the twenty-four hours is the one which occurs about eleven and a half hours after the moon crosses the meridian; and when the moon's declination is South, the one which occurs about one and a half hours after the moon's meridian passage.

6. Bis. Or, the following rule may be used, which applies when the moon crosses the meridian between midnight and 114 A. M., or between noon and 11 P. M.

If the moon is South of the Equator and passes the meridian in the morning, the high water will be higher than the afternoon high water; if it passes the meridian in the afternoon, the afternoon high water will be the higher. If the moon is North of the Equator, and passes the meridian in the morning, the afternoon high water will be the higher.

7. The lower of the two successive low waters of the twenty-four hours, occurs about seven hours after the higher of the two high waters.

8.

The average difference between the hight of the higher high water and of the lower low water, is five feet eleven and a half inches, and the greatest difference is seven feet ten inches.

The above rules were drawn up so as to avoid technical terms.