74. The Brazilian current 8 is a branch of the equatorial current and runs along the coast of the South American Continent as far as the island of Trinidad and Martin Vas Rocks, where it divides. One branch of this current runs to the southeast, where a junction with the southern connecting current 9 is effected; the other branch flows in a southwesterly direction along the coast of Uruguay and Argentine Republic, gradually losing in velocity and finally disappearing at about latitude 45° S. This current is, however, greatly affected by prevailing winds.

CURRENTS OF THE PACIFIC OCEAN

75. Equatorial Current.-Among the currents of the Pacific Ocean the equatorial current 10 is the principal one; it sets to the west across the Pacific Ocean at a variable rate, the mean of which is estimated to be about 20 to 24 miles per day. A counter current 11 has been proved to exist, setting to the eastward at some distance to the north of the equator, particularly in the western part of the Pacific.

76. The Kuro-Shiwo, or Japan Stream.-To the north of this counter current is found the northern equatorial current 12, which sets in the same direction as the mean equatorial; this current is caused by the northeast trade winds. On reaching the eastern shores of the Philippine Islands the equatorial current is deflected to the northward, forming in latitude 20° N, between the meridian of 125° E and the east coast of Formosa, the commencement of the great oceanic warm current known as the Kuro-Shiwo, or Japan stream 13, the limits and rate of which are greatly influenced by the monsoons of the China Sea and the prevailing winds in the Yellow and Japan seas. The changes in direction of this current due to monsoons, etc. should be carefully studied in Sailing Directions and Pilot Charts by those expecting to navigate in these localities.

77. The North Pacific drift current 14, which is a branch of the Japan stream, crosses the Pacific Ocean in a

general easterly direction. At about latitude 40° N and longitude 150° W, it changes into a southerly direction, joining the north equatorial current near the Sandwich Islands.

78. The Arctic current 15, which flows from Bering Strait in the direction of the North American Continent and terminates on the Mexican Coast, is not of equal magnitude and importance as the Arctic current of the Atlantic Ocean; its mean velocity is estimated to be about 1 mile per hour and usually the current is stronger near the land than at sea.

The direction and velocity of currents in the upper part of the North Pacific Ocean are, however, little known, owing to the meager reports available from that region. The Hydrographic Office on its Pilot Chart of the North Pacific Ocean (August, 1901) prints the following notice in reference to this region: "After a careful consideration of the reports of vessels cruising near the Aleutian Islands and Bering Sea, the Hydrographic Office warns mariners against placing too much reliance upon current predictions in that portion of the North Pacific."

79. The Australian Ocean current 16, which is a branch of the southern equatorial current 17, sets along the east coast of Australia; the greater part of this current makes its way to the coast of New South Wales, where it meets and is reversed by the Antarctic current 18 issuing from Bass Strait.

To the south of New Zealand strong easterly drift currents 19, 20 are found, which are produced by the prevailing westerly winds. After reaching the South American Coast one branch of these drift currents turns toward the north and runs along the coast of Peru, being known, then, as the Peruvian current 21; the other branch turns into an east-by-southeast direction and forms the Cape Horn current 22, which, after passing around Terra del Fuego, turns into a northeasterly direction and is absorbed by the southern connecting current 9.

CURRENTS OF THE INDIAN OCEAN

80. In the Indian Ocean the motion of the water north of the equator is entirely regulated by the winds. From October to April, when the northeast monsoon blows, the current runs to the westward, around the shores of the Arabian Gulf; from April to October, when the southwest monsoon prevails, the water flows in exactly the opposite direction. The great westerly equatorial drift current 23 of this ocean lies to the south of the equator and flows on until it impinges on the African Coast, where it splits into two streams. One of these turns to the south, running along the coast of Madagascar, and is finally absorbed by the easterly drift current 24, which passes south of the Australian Coast and eventually finds its way into the Pacific Ocean. The other branch of the equatorial drift current turns southward along the Mozambique Channel, and after passing the latitude of Durban, is known as the Agulhas current 6. This current is essentially a body of warm water with an occasional velocity of 4 miles an hour.

NOTE.-The foregoing brief description of the principal currents of the world will serve merely as a general guide to the student. For particulars as to the direction and velocity of the currents at certain localities, during certain months, Sailing Directions and Pilot Charts

should be consulted and studied.

TIDES AND TIDAL CURRENTS*

INTRODUCTION

81. Briefly stated, the tide is the alternate rise and fall of the water in the ocean, as seen on sea beaches, cliffs, estuaries, etc. When the water rises to the highest point it is capable of reaching on any particular day, it is called high water or high tide; when it sinks to the lowest possible ebb, low water or low tide is reached. High tides follow each other at intervals of 12 hours and 25 minutes. Low tides succeed each other at the same interval.

*Compiled by Lieut. C. A. Foster, U. S. Navy (retired).

82. Cause of the Tides.-The most potent cause in producing the tides is the moon. It is obvious that by the laws of gravitation the moon must attract the water of the ocean on the particular side on which she is at the time, and if the earth were immovably fixed, and there were no sun, this would be all; but the earth is not fixed, and in addition to drawing the water to her from the earth on one side of the globe, the moon draws the globe itself away from the water on the other side, thus making high water at the same time on opposite sides of the earth.

The sun also exerts an attraction, but, owing to his great distance, the mean force of the sun in raising the tide is to that of the moon only as 1 to 24; for though the mass of the sun is vastly greater than that of the moon, its distance causes it to attract different parts of the earth with nearly the same force. When the sun and moon exert their influence in one direction the tide produced is greater than when they counteract each other's attraction. Though to an observer on land the water seems to alternately rise and fall, yet what really takes place on the ocean at large is that the moon raises a wave, which follows her movement, thus producing high water in regular succession as the earth turns on its axis. If the earth did not revolve, tides would only occur every 14 days.

The energy producing tides is, thus, mainly of the earth, not of the moon; the store of earthly energy is therefore reduced by the tides, which act as a brake, or drag, on the revolving globe, while the energy of the moon is increased by them. The effect is to retard the rotation of the earth and to cause the moon to slowly increase her distance from the earth.

83. Tides reaching the shore are affected by its conformation. Thus, in a nearly enclosed sea like the Mediterranean, tides are only from 1 to 3 feet high. Far out in the ocean they have but a small range; thus at St. Helena they are only 3 feet, while at London they are 18 or 19 feet. At Cardiff, the greatest tides are from 37 to 38 feet and the

lowest from 28 to 29 feet; the greatest tide, that in the Bay of Fundy, is 50 feet.

84. Springs and Neaps.-Tides do not always rise to the same height, but every fortnight after the new and full moon they become much higher than they were in the alternate weeks, or after the first and last quarters of the moon. These high tides are called spring tides, and the low ones, neap tides.

85. Priming and Lagging. During the first and third quarters of the lunar month, the sun's influence tends to draw the tide wave to the westward of its position under the influence of the moon, and so tends to hasten the time of high water. This is called priming. During the second and fourth quarters, the sun has an opposite effect and tends to delay the time of high water, thus causing what is known as lagging.

86.

Slack water is when there is no horizontal movement of the water.

87. Stand is the interval during which there is no vertical movement.

88. Set applies to tides as well as currents and indicates the compass direction toward which the tide or current is flowing.

89. The drift of a tide or current is the velocity in knots per hour.

90. The range of a tide is the vertical distance between high and low water of any tide.

91. The rise of a tide is the height of its high water above its plane of reference.

92. The age of a tide is the interval of time between the time of new or full moon and the succeeding spring tide; or, in general, it is the elapsed time between a meridian