Mantchooria, the Amoor provinces and the western coast of the sea of Ochotsk, till about 60° N. L. (See Plates 5, 6, 7.)

As this last extension of the monsoon zone is not generally accepted, it is necessary to give some further details. I have already stated that on the lastnamed coast the cloudiness is double in summer of that of winter. The E. winds of summer and the W. winds which set in September or October lasting all winter are so well known to the inhabitants that they sail in July and August from Kamtschatka to Ajan or Ochotsk and return in September or October, having in each passage favorable winds. The rains have also a marked monsoon character at Ajan, only they are somewhat delayed, the largest amount falling in August and September. This is due to the great masses of ice in the sea of Ochotsk, which disappear only in the end of summer. So long as the sea is colder than the land, precipitation can not be copious, which is the case until August and September when the sea is warmer than the land.

As to the upper Amoor, the small amount of snow falling in winter and the abundant rains of summer also tend to show that this region is under the influence of the monsoons.

I give below the percentage of the prevailing winds of the different months at Hakodade (42° N. L.) and Nikolaievsk (53° N. L.) to show with how much regularity the change takes place in these northern latitudes, which were till now considered as not belonging to the monsoon regions.

India and adjacent regions have been long known to the Europeans as the classical country of the monsoons, though as we have seen their course is not less regular in China and Japan. There is a reason why the mind is more impressed with their regularity in the Indian Seas; owing to the low latitude, there is scarcely any difference of temperature between winter and summer. The change of the season from wet to dry and vice versa is then the only conspicuous feature in the course of the year. In China and Japan the difference of temperature is greater between the two seasons, and these changes more attract the attention. The inhabitant of a temperate zone finds here the habitual difference between winter and summer, and thus considers this climate as resembling his own, different as it may be in the course of the winds and the period of rains. The atmospheric pressure of the monsoon region is illustrated on Plate 14, the winds on Plates 5, 6 and 7.

SUNDA AND PHILIPPINE ISLANDS.

In the seas south of Indo-China there is a double system of monsoons. The S. E. trade crosses the equator in our summer, and gradually is changed to a S. and S. W. wind, while during our winter the N. E. trade crosses into the southern hemisphere, by and by assuming a direction from N. W. This last movement is caused by the heating and rarefaction of the air over Australia.

The Sunda Islands, being situated near the equator, are under the influence of both monsoons. The one or the other of them can bring rain, and this depends much more on local causes than on the situation north or south of the equator. The direction of the wind in this Archipelago and the surrounding seas is not only governed by the flow of air towards Asia and Australia (the great monsoons), but also by the heating and rarefaction of the air on the islands themselves, especially on the largest, Borneo and Sumatra. Even on the island of Java, narrow as it is, there are great irregularities in the course of the monsoons caused by day and night winds, at least at some seasons.1

I give here the mean direction of the winds at Batavia, from the elaborate discussion of the observations made at this place by Dr. Bergsma, director of the Observatory.

It will be seen that the west monsoon (in our winter) is much more regular than the east monsoon. Besides, in the last season, the mean direction of the wind is to the N. of E., while the S. E. trade should be expected.

This is probably due to sea and land winds, which blow more regularly and strongly, as this is a comparatively dry season.

I give next some percentages from this region, adding the Philippine Islands, where the extreme regularity of both monsoons is remarkable, while the Sunda Islands show more local deflections.

1 An excellent sketch of the winds of Java, by Lieut. Jansen, is published in Maury's "Physical Geography of the Sea."

0443 ∞ ∞

W.

N. W.

0

8 17

9 13 26

12 18 21

14 15 25

3 13 33 14

Indian Ocean and Bay of Bengal, bet. 90° & 100° E.

MONSOON REGION OF SOUTHERN ASIA.

Further west, on the Indian Ocean, and the Bay of Bengal, the following table shows the passage of the S. E. trade into the S. W. monsoon. I have given the result of observations on the eastern part of the ocean between 90° and 100° in percentages.

S. W.

W.

Between 5°-10° S. the S. E. trade prevails yet. From 0-5° S. these S. W. winds are already more frequent, which may be partly caused by the influence of Sumatra, although the S. and S. E. winds are also frequent. Between 0 and 10° N. the prevalence of S. W. is very large, but S. and W. are also well represented. North of 10° N. the S. W. winds prevail nearly to the exclusion of all others. In our winter the N. E. monsoon (or trade) largely prevails between 5° and 15° N. Between ()° and 5° N. the number of N. E. winds has decreased one-half, while N. and N. W. have increased in number, while from 0° to 10° S., west winds are the most nume

rous.

If we take a more westerly meridian, the result will be more clearly seen, as in the next table, and also on Plates 5 and 6.

Here we have from June to August the mean direction of the wind passing from S. 63° E. through S 22° E. to S. 58° W., while farther north the mean direction becomes a little more southerly, probably owing to the influence of the continent. Still more regular is the passage of the N. E. trade into the N. W. monsoon of the southern hemisphere.

In the western part of the Indian Ocean, towards the coast of Africa, we have the following percentages:

E.

December to February.

Here the S. E. trades prevail S. of 5° S.; between 0° and 5° S. there is a zone of variable winds, where S. E., S., S. W. and W. are most frequent, and north of the equator the S. W. monsoon is well established. From December to February the N. E. trades have an easterly direction between 10° and 15° N. They become more N. E. between 0° and 10° N., and between 5° and 10° S, N. W. winds are already prevailing.

Below the percentage of winds at some stations of India is given :

There is less regularity in the winds of India, taken as a whole, than in Eastern. Asia. Especially this is the case if we expect the summer monsoon to be everywhere S. W., and that of winter everywhere N. E. without regard to the position of the station towards the region of lowest pressure, and towards the ocean.'

At Calcutta the monsoons must be N. and S., as the region of lowest pressure lies to the N. W. of this place, somewhere in the Punjab, as seen on Plate 14. In the N. W. provinces of India the winds of summer are rather S. E., while N. W. and W. winds prevail in winter. The latter is a current of air from the interior of the peninsula towards the sea, and has much in common with the N. W. winds of Eastern Asia. Farther to the N. W. at Lodianah and Dehra-Doon, we are nearly out of the monsoon region. According to Blanford the winter winds begin on the plains of Northern India, where the pressure is high at that season. They flow towards the seas to the S. W. and S. E.

At Bombay there is a very slight change in the direction of the prevailing wind,

1 M. Blanford has well discussed the monsoons of Bengal and the adjoining provinces, and their relation to pressure, in "Reports of the Meteorol. Reporter of the Govt. of Bengal."

93

July, 1875,

S. W.

W.

N. W.

it being N. N. W. in winter, and W. S. W. in summer,

Yet Bombay is known to

have very marked monsoon seasons, that is, scarcely any rain falls in winter, while it is profuse from June to September. At Madras the monsoons are from the same direction as on the seas in the same latitude, N. E. in winter, S. W. in summer. The relative position of land and sea has in this case a very small influence, otherwise we should have E. and S. E. winds in summer, W. and N. W. in winter. Madras is nearly due South of the lowest pressure in summer, and the difference is sufficiently great to give the prevalence and regularity of S. W. winds.

The winds at Dodabetta, a high station on the Neilgherries, S. W. of Madras, are peculiar; N. W. winds prevail in summer and S. E. in winter. This shows that the movement of air which is experienced near the sea-level does not extend very high. The mean direction in winter and summer is more than 90° different from that of Madras and other stations of India in low latitudes, and nearly the opposite of that of Calcutta, Central India and the Punjab, as shown by the following table:—

Thus, on a great part of the continent of India, the motion of air is towards the centre of lowest pressure in the Punjab, as also seen on Plates 5, 6, and 7, while at Dodabetta, 8640 feet high, it is from the Punjab. It seems thus, that the rarefaction of air does not extend to very high regions. In the winter, on the contrary, air moves from N. W. India towards the Bay of Bengal, and in the opposite direction at Dodabetta.

Blanford considers the winds at this high station as somewhat similar to the return-trade or westerly winds blowing over the trades on tropical seas.

At Roorkee the mean pressure in January is 29.15, in June 28.62, difference 0.53 inche, at Dodabetta it is 22.18 in January, 22.09 in June, difference 0.09 in. It is also seen that the summer monsoon is shorter in the northern part of India, spring and autumn having the same direction of the wind as winter, only the ratio of resultant is smaller. At Calcutta and Madras the S. winds are already estab lished early in spring, while at Colombo, Ceylon, still farther south, spring, summer, and autumn have the same direction of wind. (See Plate 7.)

The dominating winds seem also to be the strongest. So, for example, at Bombay, the greatest mean velocities were distributed as follows: in May S. S. E. 16.5 miles an hour, June S. S. E. 27.5 miles, July W. S. W. 21.4, August S. W. 17.0, December N. N. W. 13.9, January N. N. W. 14.1, and in February N. W. 14.6.