Nova Scotia and the coast of the United States, inside the Gulf Stream. The water of this current is very cold, bringing with it large quantities of pack ice and icebergs, which it discharges into the Atlantic Ocean. A branch of the Arctic current runs in a southerly direction down along the east coast of Greenland and effects a junction with the main current in Davis's Strait.

64.

Guinea Current.-The Guinea current 3 is a drift current setting to the southward along the west coast of Africa. After passing the Cape Verde Islands, it becomes a stream current, running eastward into the Gulf of Guinea. The greatest velocity of this current is stated to be off Cape Palmas, where, at a few miles from the shore, it has been found to run more than 3 miles an hour. For about 200 miles from the coast, between Cape Verde and Sierra Leone, winds and currents change with seasons. From June to September, squally southwest winds with a northeast current prevail; while from October to May, northerly winds and southeasterly currents are experienced.

65. Equatorial Currents.-The equatorial current 4 is a vast drift current caused by the trade winds. This current commences near the southwest coast of Africa, where it is known as the South African current 5, which, again, is a continuation of the Agulhas current 6, generated by the great drifts of the Indian Ocean. Between the months of July and November, the northern edge of the equatorial current, in latitude 8° to 10° N, appears to change its direction to northeast and finally settles to the eastward toward the African Coast. This current, whose rate and width increases as it advances eastward, is called the equatorial counter current 7.

66. Brazilian Current.-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

67. 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 a 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.

68. The Kuro-Shiwo, or Japan Stream.-To the north of the counter current just mentioned 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.

69. North Pacific Drift Current. 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.

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70. Arctic Current.-The Arctic current 15, which flows from Bering Strait in the direction of the Norin American continent and terminates on the Mexican coast, is not of the same 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."

71. Other Important Pacific Currents.-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 are found strong easterly drift currents 19, 20 that 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.

197 B-29

CURRENTS OF THE INDIAN OCEAN

72. 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. 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

74.

GENERAL THEORY OF TIDES

73. As previously 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. Generally, high tides follow each other at intervals of 12 hours and 25 minutes; low tides succeed each other at the same interval. Cause of 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 its great distance, the mean force of the sun in raising the tide is to that of the moon only as 1 is to 2; for though the mass of the sun is vastly greater than that of the moon, the distance of the sun 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 rise and fall alternately, yet what really takes place on the ocean at large is that the moon raises a wave, which follows her movement,