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Arctic current and the Gulf Stream join is well marked; the warm stream is blue and the cold stream green. The current has little strength.

The north-east trade drift is due to a wind current and flows very slowly to the westward and southward before the wind and joins the equatorial current in the neighbourhood of the West Indies.

The Rennel Current This is an easterly current from the Atlantic, perhaps a portion of the Gulf Stream arrested by the westerly winds. It strikes the land on the N.W. corner of Spain and divides, one part going south along the land and towards the Straits of Gibraltar; the other part sweeps round the Bay of Biscay, passing about 15 to 20 miles off Ushant, and flows to the N.W. across the mouth of the English Channel.

The Mediterranean The current sets in from the Atlantic and is caused chiefly by the great evaporation which goes on in the Mediterranean; generally the current sets east along the African coast, and to the west from the eastern end along the coast of Europe.

The Guinca Current This current flows along the African coast to the eastward between Cape Roxo and the Bight of Biafra, extending southwards to about 3° of N. latitude. It extends to the westward as far as 23° W. longitude, extending more to the westward during the season, July to November. It attains a velocity of about 3 miles an hour off Cape Palmas and is warmer than the equatorial current.

The Cape Horn Current This is an easterly current caused chiefly by prevailing winds. After passing Cape Horn it gravitates towards the north and in about 40° south latitude joins the South Atlantic connecting current.

The circulation is completed by a small portion of the Agulhas current, which passes over the banks of that name, and branching off to the N.W. joins up with the South Atlantic Connecting Current.

Indian Ocean The equatorial current is broken into by the prevailing monsoon and does not run so true as in the Atlantic.

The S.E. trade drift is a current caused by the wind and runs to the westward at the rate of 20 to 25 miles a day between the parallels of 8° S. and 27° S. latitude. It separates on the east side of Rodriguez Island into two parts, one towards the north end of Madagascar at the rate of 40 to 60 miles a day, and the other part sweeps to the south end at the rate of 50 miles a day.

The northern branch again splits near Cape Delgado in latitude 11°S. on the African coast, one part running southward through the Mozambique Channel, in some places at the rate of 4 to 5 miles an hour.

In the latitude of Natal it again joins the stream that went south of Madagascar and forms the Agulhas Current which flows south-west and west along the African coast at a distance varying from 5 to 120 miles, attaining a great velocity between Port Natal and the twenty-third meridian, making from 4 to 4 miles per hour, its greatest strength being near the bank. It then in the main follows the edge of the bank, is deflected to the southward and then to the eastward, flowing back into the Indian Ocean with diminished speed and a lower temperature as far as 40° S. latitude. As before stated, a small portion flows round the coast to the N.W. The part that turned north off Cape Delgado runs north and north-east at the rate of 2 to 4 miles per hour and during the S.W. monsoon to the eastward across the Arabian Sea. The current runs out of the Red Sea during the S.W. monsoon and into it during the N.E. monsoon. In the Gulf of Suez and the Red Sea generally the currents are caused by the prevailing winds.

Pacific Ocean

The equatorial current, as in the other oceans, runs to the westward from near the American coast towards the east coast of Australia between the parallels of 5° N. and 20° S. latitude at a rate of half a mile to 3 miles per hour. It turns to the eastward when 40 to 60 miles from the Australian coast and helps to form the equatorial counter current which flows between the parallels of 5° and 8° north latitude.

The N.E. trade drift runs to the westward between 9° and 20° north latitude and is deflected by the Philippine Islands to the northward, forming the commencement of the Kino Sirvo which flows along the east coast of Formosa and Japan, sweeps along the south-eastern coast of Japan until it reaches the parallel of 50°N., where it is known as the Kamschatka current. The Oya Sirvo is a cold water current from the Kamschatka and Kuril Islands, running southward along the east coast of Yezo Island, the N.E. coast of Nipon, and inside the Kino Sirvo.

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China and Java Seas In the China Seas the currents set with the prevailing monsoon at a varying rate of a half to 2 miles per hour, but on the east coast of China and to the eastward of the Pescadores Islands the northerly current sometimes runs 3 to 4 miles hour.

The currents in the Java Seas are influenced in the same manner by the prevailing monsoon, and are generally stronger in the N.W. than in the S.E. monsoon, in the former, running at the rate of a mile an hour, in the latter, at half a mile an hour. Where the waters are confined in narrow channels the currents run much more rapidly and are complicated by the tides and are therefore uncertain and irregular.

The student will notice that, throughout, one current flowing away induces another, forming complete chains wherever the seas run.

For more detailed information on “Ocean Currents ” see the Sailing Directions for the various Oceans.

INTRODUCTION TO NAUTICAL

ASTRONOMY To understand that branch of navigation which is based upon nautical astronomy it is necessary that the student should have a clear conception of the earth's position in the solar system and in the stellar universe. The following chapter is written for that purpose, and is purely elementary.

For further information consult a Elementary Lessons in Astronomy” (Lockyer), “The Story of the Stars” (Chambers), “Introduction to Astronomy” (Moulton), etc.

Imagine the earth reduced to a globe a few feet in diameter, and upon which we are so situated that we can see the sky in all directions. The sun's light would pervade everywhere, we should see nothing but, perhaps, a faint reflection from the moon.

To enable us to see the stars the sun's light must be blotted out; the planets, their satellites, and the moon would also disappear, because they shine with light ieflected from the sun. We should be in complete darkness except for the faint light received from the stars. With normal sight we should see scattered about the sky about seven thousand stars, probably less—not the countless numbers generally supposed. All the stars would be in view, but nothing new, only the familiar stars in lonely splendour or clustered in beautiful constellations. They would be spread before us apparently in endless confusion, but with a little acquaintance they soon take order and are easily recognised.

If we look up into the northern sky we shall see Polaris, the North Star in the constellation of Ursa Minor, the North Pole of the heavens, round which all the stars in the Northern Hemisphere swing. Far down in the southern sky faintly gleaming close to the South Pole can be seen Sigma Octantis; midway between lies a broad band of stars sweeping right round the heavens, the signs of the Zodiac, that thousands of years ago represented the months and seasons; a starry calendar, recording the sun's annual progress, and still familiar to us as Aries, representing Spring, Cancer, the Summer, Libra, the Autumn, and Capricornus, Winter.

An ancient rhyme gives the signs thus :

The Ram, the Bull, the heavenly Twins,
And next the Crab the Lion shines,

The Virgin and the Scales ;
The Scorpion, Archer, and He-goat,
The man that holds the water-pot,

And Fish with glittering tails.

Put into their latinised names they are : Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricornus, Aquarius, and Pisces. Between this equatorial band and the poles are many other constellations, stars of various brightness and colour, all suns much like our own sun, shining with their own light, but at such an immense distance that they are reduced call

to a point of light. No ordinary measurement can convey any idea of their distances. The measurement commonly used is the distance light travels in a year, and since light travels 186,333 miles per second, the distance in a year will be equal to 186,333 X 60 X 60 X 24 X 365—an inconceivable figure. Yet the nearest star to the Solar System, a Centauri, is distant four and a half years, and the most remote are estimated to be from.2,000 to 3,000 years distant. We can form a fair idea of the distance in another way. If we had a Morse flash-lamp powerful enough to reach the stars we could

up the moon in one and a half seconds, the sun in a little more than eight minutes, the nearest star in four and a half years. In the centre of this tremendous space the sun, “simply one star in the universe ”is situated, surrounded by his family of eight planets. From this great multitude of stars the navigator selects about twenty of the brightest to assist him to find his way across the seas, but he must know them with precision. How is he to do this?

At this stage the astronomer comes to his aid He draws horizontal and vertical lines (really portions of immense circles) upon the surface of the sky on the same principle that geographers draw parallels of latitude and meridians of longitude upon the earth's surface. The earth's poles are extended indefinitely until they reach the sky, the North Pole almost touching Polaris, and the South Pole Sigma Octantis. The earth's equator is also extended till it meets the stars, but this greater circle is called the equinoctial. Lines are drawn parallel to the equinoctial both above and below until the poles are reached. They are really circles which diminish in circumference, parallels of declination. Then great circles are drawn from pole to pole, cutting all these parallel circles at right angles, and are called meridians or hour circles. Imagine the sky now ruled by parallel and vertical lines, which, at the equinoctial, form squares, and at the poles triangles. It is only necessary to mark the intersection of parallel and hour circle to be able to fix the position of any object in the heavens. But two starting-points are necessary from which to measure, one upwards and downwards, the other to the right or left.

The equinoctial supplies the first from which declination is measured in degrees from oo to 90° north or south. The second point requires a little explanation.

The sun in the course of a year traces a great circle among the stars, called the ecliptic; the equinoctial is also a great circle. If the ecliptic is horizontal the equinoctial is tilted about 237°, and as the one circle fits the other they must cut in two exactly opposite points—one where the sun ascends into northern declination, the other where it descends into southern declination.

Astronomers closely observed where the sun crossed the equinoctial going from south to north declination, and when its exact centre was on the intersection of the two circles a mark was made through them on to the sky beyond. As it happened, this mark did not fall on any star, it was simply an imaginary mark in a group of stars called Aries; it was called a point, a first point, the first point of Aries, and thus the second place from which to measure to the right or left was established.

If the mark was made to-day it would be 30° more to the westward, in the constellation of Pisces. This is due to a backward movement of about 50” annually, called the precession of the equinoxes. It is caused

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by the action of the sun and moon upon the earth's equatorial protuberance. They pull the equator downwards, causing the crossing point to constantly recede. Having established a point in the sky it is used as Greenwich is used, the first meridian is drawn through it, but with this difference -longitude is measured in degrees east and west from Greenwich, but from the first point of Aries right ascension is measured in hours, minutes, and seconds right round eastward from o hours to 24 hours. We now have a complete set of vertical and horizontal lines. Suppose the beginner knows one bright star, Sirius, for instance, and wished to find Rigel. He simply compares the right ascension and declination

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Therefore Rigel will be found about N. 71° W. 25° distant from Sirius. Any other celestial object can be found in the same way. The right ascension and declination of 56 bright stars is given in Norie's Tables.

It will be seen that the 7,000 visible stars are not scattered without order through space, but that each star has its name or number, its right ascension and declination recorded. The stars visible to the naked eye have been gathered into groups called constellations. In very ancient times they were given the names now familiar to us, of men, birds, beasts, and fishes. In the constellations, generally speaking, the brightest stars have proper names, and in addition take the first letter of the Greek alphabet and the name of the group. Sirius is also a Canis Major, the Great Dog, Rigel, is B Orionis, and so on. When the Greek letters are exhausted the remaining stars are numbered in Flamsteed's catalogue, and when these are used up Lalande’s and Lacaille's, etc., are referred to. Altogether, ancient and modern, there are 84 constellations. The most casual observer will notice that stars differ considerably in brightness, or, as it is called, magnitude. The term magnitude means their apparent brightness, not their size, which in most cases is not known. The visible stars are divided into six magnitudes. On reference to the Nautical Almanac and other stellar tables, it will be seen that the marking is peculiar. Sirius, the brightest star in the sky, is marked-14, and Canopus, the brightest southern star, - 1'0; Capella is o‘2, Aldebaran I'I, Markab 2:6, Orionis 4:6, etc. If stars like Vega O'I are used as a standard then Sirius and Canopus are brighter by 1'3 and 9 respectively, and the others less bright according to the figures attached. As the magnitudes decrease so do the numbers of the stars increase, especially as the limit of vision is approached. A little attention will also discover that the stars are of different colours. Some are white with a bluish tinge like Sirius or Vega, some yellow like Capella, some have an orange colour like Arcturus, and some are red like Aldebaran, Antares, and Betelguese. The stars have what is called an apparent and a proper motion. This is very small and can only be detected by a telescopic observation

The apparent motion is the movement as seen from the earth, the proper is the actual movement deduced by calculation in reference to the sun. These motions are of no consequence to the navigator beyond the

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