INDIAN OCEAN.

I have given before some figures relating to the northern part of the Indian Ocean. Unfortunately we are far from knowing the winds of this ocean so well as those of the Atlantic. The limits of the trades especially are more uncertain. The position of the Indian Ocean is such, that only the S. E. trade is developed to its full extent, and in our summer, is attracted towards the heated continent of Asia, and, owing to the rotation of the earth, gradually becomes a S. W. wind. There is no equatorial belt of calms at that season, and a reference to the map of isobars, Plate 14, will show that pressure increases then from the polar limits of the S. E. trade, about 25° S. uninterruptedly to the continent of Asia. This is also the explanation of the S. W. Monsoon, which is only the deflected S. E. trade.

Even in our winter (December to February) the winds in the Indian Ocean are under the influence of continents. In the northern part the winds are N. W., that is the N. E. trade crosses the equator, and is drawn towards the heated continent of Australia. Nearer to Africa, the winds are N. E. at this season, also occasioned by a deflection of the trade-wind towards the tropical and sub-tropical part of Africa. Thus, on the whole, the Indian Ocean is more under the influence of the continents than the Atlantic. The following table gives the direction of the winds:

There seems not to be a great difference between the limits of the N. E. trades in the eastern and western part of the Indian Ocean at all equal to that in the Atlantic. In Zone 25 (30° to 35° S.) we see a certain predominance of S. W. winds, which in the southern hemisphere correspond to the N. W. in the northern. In the North Atlantic Ocean there is a zone of prevailing northerly winds, rather N. W. than N. E. Thus in the Indian Ocean, especially near the coast of Africa (25° to 30° E.) we are already out of the S. E. trade, while S. and S. W. are yet prevailing. (See Plates 5, 6 and 7.)

Between 35° and 40° S. the westerly winds prevail very largely, and further south the number increases. Besides the large percentage of winds from this direction, they are also very strong, and in all respects prevail more extensively than in the corresponding latitudes of the northern hemisphere. It will be seen that the difference of pressure between north and south is here very great, the pressure being very low in the Antarctic regions, and high at the S. limit of the S. E.

trade. This produces the N. W. and west winds, while the great expanse of sea gives them additional strength. The only part of the northern hemisphere where the isobars are at all as close is the northern part of the Atlantic Ocean between 45° and 65° N. (See Plate 14.) Westerly winds prevail there, and are strong, but they cannot acquire full strength, as they have not so broad an expanse of ocean to blow over.

AUSTRALIA AND NEW ZEALAND.

The winds of Australia and New Zealand are largely modified by the influence of the continent. This is indicated by the following table:—

The monsoon character of the winds in Australia is very marked. Somerset, on the N. coast 10° L. S., has still the regular monsoons of the Sunda Islands. From November to February the N. E. monsoon of India and China is drawn towards the southern hemisphere as a N. W. monsoon, and brings with it clouds and rain. In the other months the S. E. trade prevails very strongly, while the N. W. wind is said to be generally weak.

Further, in Queensland we have W. and S. W. from June to August (continental winds) and N. E. and E. from December to February (sea winds). Thus the air is drawn towards the continent in summer, when Australia is heated, and in winter, on the contrary, the wind blows from the land towards the sea, as also shown by Plates 5 and 6.

The colonies of Victoria and South Australia being situated on the south coast of the continent, the land and sea winds have not the same direction here as on the eastern coast. They have N. and N. E. winds in the cold season, and S. E., S., and S. W. in the warm. West Australia has decidedly N. E. winds from June to August, and S. W. from December to February.

Tasmania is somewhat under the influence of Australia, but here the winds begin already to assume the normal maritime character, especially on the small islands of Kent's group, near Tasmania.

In New Zealand the influence of the land is far from being as important as in Australia, and westerly winds largely prevailing as on the sea in the same latitudes (36° to 47° S.). There is a difference between the east and the west coast of the south island, separated as they are by the high and steep chain of the New Zealand Alps.

PACIFIC OCEAN.

As in the case of the Indian Ocean, the materials for the study of the winds of the Pacific are the percentage of the winds, as collected by Prof. Coffin, selections from which are given in the following table:

Many of them are
Another influence

What distinguishes the Pacific Ocean from the Atlantic is a less regular S. E. trade, which seems to be caused by the numerous islands of Polynesia. high, volcanic, so as to intercept the wind for a certain distance. exerted by these islands is the local rains, which are produced by them, partly by condensation of the vapor brought by the trade; partly due to local calms and the ascending current. These condensations of vapor cause a lower pressure, and the movement of the surrounding air to supply the deficiency causes irregular winds.

For the whole year.

1

Especially in the central and western part of the ocean (between 10°-20° S.), are these irregularities noted. It will be seen that in these parallels the S. F. trade is very regular in the Atlantic Ocean. (Plates 5 and 6.)

The inner boundaries of the S. E. and N. E. trade are given as follows by Kerhallet in his "Considerations Générales sur l'Ocean Pacifique.

S. E. Trade

N. E. Trade.

April
May

5° N.
2° N.
5° 50′ N.
2° N.
3° 36′ N.

12° 5' N.

S. E. Trade. 5° 4' N.

September
October.

These observations show that the belt of equatorial calms is always north of the equator. It seems that the figures given by Kerhallet are taken from observations in the eastern part of the ocean, near the American coast, where really the S. E. trade crosses the equator. The wide limits between the two trades in summer are caused by the prevalence of the S. W. monsoon on the coasts of Central and South America. (See Plates 5, 6 and 7.)

In other parts of the Pacific Ocean the equatorial calms seem to be nearer to the equator, and partly even south of it. According to the statements of numerous navigators the trades are also more easterly there, and often do not leave any calmbelt between them, so that a ship can sail from the one into the other trade without interruption, as was also stated for the western part of the Atlantic Ocean.

The northern limit of the N. E. trade is also in a comparatively low latitude in these parts, as shown, for example, by the observations at the Sandwich Islands. They seem to be already in the zone of variable winds in the winter, N. E. and S. W., the one being noticed about as frequently as the other. Rains are also frequent in this season, with S. W. winds, thus corroborating the testimony of the wind observations.

The system of winds along the western coast of America has been already discussed.

As to the middle latitudes of the southern hemisphere in the Pacific, the same may be said of them as of the same latitudes of the Atlantic, and Indian Oceans.

ANTARCTIC ZONE.

I give next some calculations from the extreme southern part of the Pacific and Antarctic Oceans, comprising the most southerly latitudes to which man has yet penetrated.

1 See Pilot Chart of Atlantic, Pacific and Indian Ocean, edited by the British Admiralty. Unfortunately I could not obtain it in Washington, and thus have not the possibility of tracing the limits of the trades and monsoons according to the best source, as in the Atlantic.

The observations in these high southern latitudes are very conclusive; from the zone of the most prevailing westerly winds between 50° and 60°, we pass to a region of southerly and easterly winds further south. The latitudes at which these winds become prevailing are not the same in the whole Antarctic Ocean. South of Cape Horn W. and N. W. winds largely prevail between 60° and 62° S., and further south there are no observations in these meridians. Southeasterly winds are already prevailing in the meridians of the Atlantic Ocean, between 60° and 65° S., and also south of Australia, while again on the meridian of New Zealand 160° to 176° E., westerly winds are the most frequent. This seems to depend much on the currents of the sea. Where warm currents carry a high temperature further south, pressure will be lower there than in the same latitudes generally, and westerly winds will also extend further southward. Between 65° and 70° S. Lat., on the meridian of New Zealand, there is already a slight prevalence of southerly winds. Between 70° and 78° S. the observations of Sir James Ross show this to be largely the case.

Thus the hypothesis of Prof. Coffin as to the prevalence of polar winds (S. and E.) is shown to hold good also for the southern hemisphere, notwithstanding the small number of observations we possess from high southern latitudes. As to the division-line from the W. and N. W. winds of the temperate regions, it cannot yet be traced with precision.