Physical Geography of the Sea and its Meteorology/Chapter 16

by Matthew Fontaine Maury

CHAPTER XVI.

§ 681-711.—MONSOONS.

681. The cause of.—Monsoons are, for the most part, trade-winds deflected. When, at stated seasons of the 3^ear, a trade-wind is turned out of its regular course, as from one quadrant to another, it is regarded as a monsoon. The African monsoons of the Atlantic (Plate VIII.), the monsoons of the gulf of Mexico, and the Central American monsoons of the Pacific are, for the most part, formed of the trade-winds which are turned back or deflected to restore the equilibrium which the overheated plains of Africa, Utah, Texas, and New Mexico have disturbed; these winds, carrying their fuel (§ 254) with them in vapour, have their equilibrium still further disturbed by the heat which is liberated when that vapour is condensed. Thus, with regard to the N.W. and the S.W. monsoons of the Indian Ocean, for example: a force is exerted upon the N.E. trade-winds of that sea by the disturbance which the heat of summer creates in the atmosphere over the interior plains of Asia, which is more than sufficient to neutralize the forces which cause those winds to blow as trade-winds; it arrests them and turns them back; but, were it not for the peculiar conditions of the land about that ocean, what are now called the N.E. monsoons would blow the year round; there would be no S.W. monsoons there ; and the N.E. winds, being perpetual, would become all the year what in reality for several months they are, viz., N.E. trade-winds.

682. The region of.—Upon India and its seas the monsoon phenomena are developed on the grandest scale. These remarkable winds blow over all that expanse of northern water that lies between Africa and the Philippine Islands. Throughout this vast expanse, the winds that are known in other parts of the world as the N.E. trades, are here called N.E. monsoons, because, instead of blowing from that quarter for twelve months, as in other seas, they blow only for six. During the remaining six months they are turned back, as it were; for, instead of blowing towards the equator, they blow away from it, and instead of N.E. trades we have S.W. monsoons.

683. A low barometer in Northern India.—If the N.E. trade-winds blow towards the equator by reason (§ 657) of the lower barometer of the calm belt there, we should—seeing them turned back and blowing in«the opposite direction as the S.W. monsoon—expect to find towards the north, and at the place where they cease to blow, a lower barometer than that of the equatorial calm belt. The circumstances which indicate the existence of a lower summer barometer—the period of the S.W. monsoon—in the regions about northern India are developed by the law which (§ 657) requires the wind to blow towards that place where there is least atmospheric pressure.

684. The S.W. monsoons "backing down."—The S.W. monsoons commence at the north, and " back down," or work their way towards the south. Thus they set in earlier at Calcutta than they do at Ceylon, and earlier at Ceylon than they do at the equator. The average rate of travel, or "backing down to the south," as seamen express it, is from fifteen to twenty miles a day. It takes the S.W. monsoons six or eight weeks to "back down" from the tropic of Cancer to the equator. During this period there is a sort of barometric ridge in the air over this region, which we may call the monsoon wave. In this time it passes from the northern to the southern edge of the monsoon belt, and as it rolls along in its invisible but stately march, the air beneath its pressure flows out from under it both ways—on the polar side as the S.W. monsoon, on the equatorial as the N.E.

686. How they begin.—As the vernal equinox approaches, the heat of the sun begins to play upon the steppes and deserts of Asia with power enough to rarefy the air, and cause an uprising sufficient to produce an indraught thitherward from the surrounding regions. The air that is now about to set off to the south as the N.E. monsoon is thus arrested, turned back, and drawn into this place of low barometer as the S.W. monsoon. These plains become daily more and more heated, the sun more and more powerful, and the ascending columns more and more active; the area of inrushing air, like a circle on the water, is widened, and thus the S.W. monsoons, "backing down" towards the equator, drive the N.E. monsoons from the land, replace them, and gradually extend themselves out to sea.

686. The sun assisted by the latent heat of vapour.—Coming now from the water, they bring vapour, which, being condensed upon the hill-sides, liberates its latent caloric, and so, adding fuel to the flame, assists the sun (§ 648) to rarefy the air, to cause it to rise up and flow off more rapidly, and so to depress the barometer still more. It is not till the S.W. monsoons have been extended far out to sea that they commence to blow strongly, or that the rainy season begins in India. By this time the mean daily barometric pressure in this place of ascending air, which is also a calm place, has become less than it is in the equatorial calm belt; and the air which the S.E. trade-winds then bring to the equator, instead of rising up there in the calm belt, pass over without stopping, and flows onward to the calms of Central Asia as the S.W. monsoon. It is drawn over to supply the place of rarefaction over the interior of India.

687. The rain-fall in India.—The S.W. monsoon commences to change at Calcutta, in 22° 34′ N., in February, and extends thence out to sea at the rate of fifteen or twenty miles a day; yet these winds do not gather vapour enough for the rainy season of Cherraponjie, in lat. 25° 16′, to commence with until the middle or last of April, though this station, of all others in the Bengal Presidency, seems to be most favourably situated for wringing the clouds. Selecting from Colonel Sykes's report of the rain-fall of India, those places which happen to be nearest the same meridian, and about 2° of latitude apart, the following statement is made, with the view of showing, as far as such data can show, the time at which the rainy season commences in the interior:

	Lat.		Long.		March.	April.	May.	June.	July.	Aug.	Sept.	Oct.
	°	′	°	′
Poorie	19	48	85	49	..	1	1	5	14	7	4	..
Baitool ....	21	51	77	58	..	..	1	4	15	9	4	..
Saugor....	23	50	78	47	..	..	2	2	15	12	13	1
Humeerpore	26	7	79	47	..	..	..	7	13	11	5	1
Bareilly ..	28	12	79	34	..	..	..	3	17	8	2	3
Ferozepore	30	57	74	41	..	..	..	1	19	..	..	..
Simla	31	6	77	11	1	..	1	4	18	12	..	..
Cherraponjie	25	16	91	43	1	28	115	147	99	104	72	40
					2	29	120	173	210	163	100	45

It is June before the S.W. monsoons have backed down as far as the equator and have regularly set in there.

688. Its influences upon the monsoons.—These positions are selected without regard to elevation above the sea level. Of course, when the S.W. monsoon comes only from a short distance out to sea, as in April it does, it is but lightly loaded with moisture. The low country cannot condense it, and it then remains for the mountain stations in the interior, such as Cherraponjie, to get the first rains of the season; and a most interesting physical problem may be here put on the road to solution by the question:—Does not the rainy season of the S.W. monsoon commence at the high stations in the interior, as on the sides of the Himalaya, earlier than in the flat country along the sea-coast?

689. The march of the monsoons.—With the view of investigating certain monsoon phenomena, recourse was had to our great magazine of undigested facts, the abstract logs; and after discussing not less than 11,697 observations on the winds at sea between the meridians of 80° and 85° E., and from Calcutta to the equator, results were obtained for the following table, in which is stated in days the average monthly duration of the N.E. and S.W. winds at sea between the parallels of—

	22° and 20° N.		20° and 15°N.		15° and 10° N.		10° and 5° N.		5° and 0° N.
	Days.	Days.	Days.	Days.	Days.	Days.	Days.	Days.	Days.	Days.
	N.E.	S.W.	N.E.	S.W.	N.E.	S.W.	N.E.	S.W	N.E.	S.W.
January	17	6	21	2	23	1	20	1	19	3
February	11	11	13	6	19	3	22	1	16	2
March	4	[1]18	7	15	18	5	13	0	15	2
April	2	24	2	[1]22	6	12	6	11	4	14
May	1	26	1	24	3	[1]21	1	[1]23	0	[1]19
June	0	28	1	27	0	29	1	25	0	24
July	2	24	1	27	0	30	0	28	0	24
August	0	28	1	24	0	24	1	22	0	18
September	6	14	1	18	0	23	0	26	1	18
October	9	6	12	[2]6	8	10	6	16	4	14
November	11	6	25	2	21	[2]2	10	6	5	14
December	27	0	26	1	24	1	15	[2]3	12	11
Setting in of the S.W. monsoon. Ending of the S.W. moonson.

It appears from this table that between Calcutta and the S.W. monsoons are the prevailing winds for seven the N.E. for five. the line months.

690. Their conflict—it begins at the north.—Resorting to the graphic method of engraved squares for a farther discussion of these figures, it appears by the subjoined Diagram B, that in

February the north-east and south-west winds are in equal conflict between the parallels of 20° and 22°; that in March the former have been "backed down" (§ 684) as far as the parallel of 16°-15°—the medial line between them from which each monsoon is blowing—and where, again, the conflict of "back to back" is equally divided as to time of mastery (12 days) on: either side. By the month of June they (the south-west) have fairly gained the ascendancy, and so remain masters of the field until October, when the bi-annual conflict is again commenced at the north. The vanquished north-east trades now lead off in the attack, and, as the Diagram C shows, the two combatants have force enough about the parallel of 15° north to blow during this month 9 days each. The conflict, instead of being "back to back," is now face to face; instead of blowing away from the medial line, they blow towards it; instead of being a place of high, the medial line is now (§ 657) a place of low barometer. By November the north-east monsoon has pushed the place of equal contest as far down as the parallel of 5° north.

691. The barometric descent of the monsoons.—Each monsoon, like the trade-winds, blows from a higher to a lower barometer. Taking tip the clew from this fact, and resorting again to the graphic method for illustration, we may ascertain, with considerable

accuracy, not only the relative strength of the north-east and south-west monsoons of the sea, but also the mean height of the barometer in the interior of India during the south-west monsoon, supposing that monsoon to go no farther than the mountain range, which may be taken at a mean to be about the parallel of 30° north. Now, taking the mean height of the barometer at the equatorial calm belt to be (§ 362) 29.92 inches; the mean height in the calm belt of Cancer to be 30.21 inches, the line N.E. of the Diagram D will represent the average barometric declivity of the north-east monsoons generally. The mean height of the barometer during the three months of June, July, and August, when the south-west monsoons are at their height, is,

For Calcutta	29.55 inches.
⁠,,Bombay	29.65
⁠,,Madras	29.73

The line S.W. represents the mean barometric declivity of the south-west monsoons at their height, and indicates that at their

northern edge, supposed to be the parallel of 30° north, the barometer stands at about 29.45 inches. This barometric declivity indicates that the south-west are stronger than the north-east monsoons, and observations show that they are.^[1]

692. The summer rains of Cherraponjie.—These are the winds—the south-west monsoons—which, coming from the sea, carry into the interior rains for the great water-shed of India. They bear with them an immense volume of vapour, as is shown by the rivers, and confirmed by the rain-fall of Cherraponjie, and at 126 other stations. Cherraponjie is 4,500 feet above the sea level. It reaches quite up to the cloud region, and receives a precipitation of 537⅓ inches during the south-west monsoon, from May to August inclusive. Col. Sykes reported to the British Association, at its meeting in 1852, the rain-fall at these 127 places, which are between the parallels of 20° and 34° in India. According to this report, the south-west monsoons pour down during the three summer months upon this water-shed 29¾ inches of rain. The latent heat that is liberated during the condensation of the vapour for all this rain expands the air, causing it to boil over, flow off, and leave a low barometer—a diminished atmospheric pressure throughout all the region south of the Himalaya.

693. Dove and the monsoons.—As long ago as 1831, Dove maintained that the south-west monsoon was the south-east trade-wind rushing forward to fill the vacant places over the northern deserts. Dove admits the proofs of this to be indirect, and acknowledges the difficulty of finding out and demonstrating the problem.

694. The south-east trades passing into south-west monsoons.—But any navigator who, during the summer months, has occasion to traverse the Indian Ocean from north to south, may find that it is so. The outward-bound Indiaman, who, when on his way to Calcutta, crosses the equator in August, fur example, will find the south-east trades, as he approaches the line, to haul more and more to the south. As he advances still farther north they get to the west of south. Finally, he discovers that he has got the regular south-west monsoons, and that he has passed from the south-east trades into them without any intervening calm. This in summer is the rule; it has its exceptions, but they are rare. Examining the logs of a number of vessels taken at random for the passage in August, we find, by 421 observations therein recorded, they had the wind thus:

Wind from	S.E.	between	Lat. 10° and 5° S	with	0	calms.
,,	S.	,,	50 S. and Equator	,,	3	,,
,,	S.W.	,,	Equator and 5° N.	,,	3	,,
,,	S.W.	,,	Lat. 50 and 10° N.	,,	0	,,

695. Lieutenant Jansen.—In like manner, and with like force, Jansen maintains that the north-west monsoon of Australia is the north-east trade-wind turned aside.

696. Monsoons in the Pacific.—The influence exerted upon rainless winds by the deserts of Africa and the overheated plains of Asia is felt at sea for a thousand miles or more. Thus, though the desert of Cobi and the sun-burned plains of Asia are, for the most part, north of latitude SO"", their influence in assisting to cause monsoons (§ 692) is felt south of the equator (Plate VIII.). So, too, with the great desert of Sahara and the African monsoons of the Atlantic; also with the Salt Lake country and the Mexican monsoons on one side, and those of Central America in the Pacific on the other. The influence (§ 298) of the deserts of Arabia upon the winds is felt in Austria and other parts of Europe, as the observations of Kriel, Lamont, and others show. So, also, do the islands, such as the Society and Sandwich, that stand far away from any extent of land, have a very singular but marked effect upon the wind. They interfere with the trades very often, and turn them back; for westerly and equatorial winds are common at both these groups in their winter-time. Some hydrographers have even taken those westerly winds of the Society Islands to be an extension of the monsoons of the Indian Ocean.

697. Influences of coral reefs upon winds.—It is a curious thing is this influence of islands in the trade-wind region upon the winds in the Pacific. Every navigator who has cruised in those parts of that ocean has often turned with wonder and delight to admire the gorgeous piles of cumuli, heaped up and arranged in the most delicate and exquisitely beautiful masses that it is possible for fleecy matter to assume. Not only are these cloud-piles found capping the hills among the islands, but they are often seen to overhang the lowest islet of the tropics, and even to stand above coral patches and hidden reefs, "a cloud by day," to serve as a beacon to the lonely mariner out there at sea, and to warn him of shoals and dangers which no lead nor seaman's eye has ever seen or sounded out. These clouds, under favourable circumstances, may be seen gathering above the low coral island, and performing their office in preparing it for vegetation and fruitfulness in a very striking manner. As they are condensed into showers, one fancies that they are a sponge of the most delicately elaborated material, and that he can see, as they "drop down their fatness," the invisible but bountiful hand aloft that is pressing it out.—Maury's Sailing Directions, 7th ed., p. 820.

698. Monsoons in miniature.—Land and sea breezes are monsoons in miniature, for they depend in a measure upon the same cause. In the monsoons, the latent heat of vapour which is set free over the land is a powerful agent. In the land and sea breezes, the heat of the sun by day and the radiation of caloric by night are alone concerned. In the monsoons the heat of summer and cold of winter are also concerned. But could the experiment be made with two barometers properly placed—one at sea and the other on land, but both within the reach of land and sea breezes—they would show, I doubt not, regular alterations of pressure. In the sea breeze, the land barometer would be low and the sea high, and vice versa in the land breeze; and when the barometer was highest and when it was lowest it would be calm at the barometric stations.

699. The changing of the monsoons.—It is these calm bands or "medial belts," as the crest and trough of the barometric wave may be called, which, with their canopy of clouds, follow the departing and herald the coming monsoon. They move to and fro, up and down the earth, like the sun in declination. As they have a breadth of 200 or 300 miles, they occupy several days in passing any given parallel, and while they overshadow it, then the monsoons are dethroned. During the interregnum, which lasts a week or two, the fiends of the storm hold their terrific sway in these bands. The changing of the monsoons is marked by storm and tempest. Becalmed in them, meanings are said by seamen to be heard in the air—a sign of the coming storm—a warning of impending danger to ship and crew. Then the props and stays are taken away from the air, and the wind seems ready to rush violently hither and thither, and whenever there is from any cause a momentary disturbance of the equilibrium. In such an atmosphere, the latent heat that is liberated by every heavy rain-shower has power to brew a storm. Throughout the monsoon region, the people know beforehand, almost to a day, the coming of this interregnum, which they call the changing of the monsoons, for the annual changing at the same place is very regular.

700. How the calm belt of Cancer is pushed to the north.—Theory, therefore, points to a place in Northern India, which is near the northern limits of the south-west monsoon, where the mean height of the barometer during the rainy season (§ 691) is about 29.5 inches, the mean height at the equator being 29.92 inches. Into this monsoon place of low barometer over the land the wind rushes from the north-east as well as the south-west. The place of high pressure towards the north from which it rushes is under the calm belt of Cancer. Hence this belt is also pushed north, and made to occupy, in summer at least, the position over land somewhat like that assigned to it on Plate VIII. In the south-west monsoon the Malabar coast has its rainy season, so that the air over the peninsula is permanently kept more or less in a rarefied state, by the liberation of latent heat from vapour as actual observations abundantly show.

701. The curved form of the equatorial calm belt in the Indian Ocean.—The equatorial calm belt in the Indian Ocean is a decided curve. The peculiar form may be ascribed to the meteorological influence of the Indian peninsula upon the calm belt, and in this way: The north-east monsoon brings the rainy season to the Coromandel coast and to the east coast of Ceylon. This rainy season embraces the land rather than the sea. The latent heat that is liberated during these rains, together with the effect of the solar ray upon this tongue of land, has the effect of expanding the air over it, and so "deadening" the north-east monsoon. In the mean time, the meteorological influences from Africa on one side, and Australia on the other, tend to draw the wind in towards those lands and so retard the edges of the south-east trades, thus giving the calm belt the curved form shown in the plate.

702. The winter monsoons,—In the winter-time, and during the north-east monsoon, there is in the calm belt which intervenes between that monsoon and the south-east trades, a belt of winter or westerly monsoons. It, too, is curved, as shown (Plate VIII.) by the two lines drawn to represent its mean limits about the 1st of March. This is a most remarkable phenomenon, for which no satisfactory explanation has been suggested. It extends nearly, if not entirely, across the Pacific Ocean also, and the winds all the way in it prevail from the westward. The extreme breadth of this winter monsoon belt is about 9° or 10° of latitude. In the Indian Ocean, its middle is between the equator and 5° S.; in the Pacific, between the equator and 5° N. in the Atlantic, between 5° and 10° N. In the Atlantic it is a summer monsoon easily to be accounted for. This belt of sub-monsoons, considering its great length and small breadth, is one of the most remarkable phenomena in marine meteorology.

703. The monsoons of Australasia.—The north-west monsoons of Australia come from this belt; there it is widened, for these winds extend far down the west coast of that continent. The Malayan and Australasian archipelago have a complication of monsoons and sub-monsoons. The land and sea breezes impart to them peculiar features in many places, especially about the changing of the monsoons, as described by Jansen in his appendix to the Dutch edition of this work: "We have seen," says he "that the calms which precede the sea breeze generally continue longer, and are accompanied with an upward motion of the air, that, on the contrary, those which precede the land-breeze are, in the Java Sea, generally of shorter duration, accompanied by a heavy atmosphere, and that there is also an evident difference between the conversion of the land breeze into the sea breeze, and of the latter into the former. Even as the calms vary, so there appears to be a marked difference between the changing of the monsoons in the spring and in the autumn in the Java Sea. As soon as the sun has crossed the equator, and its vertical rays begin to play more and more perpendicularly upon the northern hemisphere, the inland plains of Asia, North Africa, and of North America are so heated as to give birth to the south-west monsoons in the China Sea, in the North Indian Ocean, in the North Atlantic, and upon the west coast of Central America: then the north-west monsoon disappears from the East Indian Archipelago, and gives place to the south-east trade-wind, which is known as the east monsoon, just as the north-west wind, which prevails during the southern summer, is called the west monsoon. This is the only north-west monsoon which is found in the southern hemisphere. While in the northern hemisphere the north-east trade-wind blows in the China Sea and in the Indian Ocean, in the East Indian Archipelago the west monsoon prevails; and when here the south-east trade blows as the east monsoon, we find the south-west monsoon in the adjacent seas of the northern hemisphere. Generally the westerly monsoons blow during the summer months of the hemisphere wherein they are found.

704. Thunder and lightning.—"In the Java Sea, during the month of February, the west monsoon blows strong almost continually; in March it blows intermittently, and with hard squalls; but in April the squalls become less frequent and less severe. Now the changing commences; all at once gusts begin to spring np from the east: they are often followed by calms. The clouds which crowd themselves upon the clear sky give warning of the combat in the upper air which the currents there are about to wage with each other. The electricity, driven thereby out of its natural channels, in which, unobserved, it has been performing silently, but with the full consciousness of its power, the mysterious task appointed to it, now displays itself with dazzling majesty; its sheen and its voice fill with astonishment and deep reverence the mind of the sailor—so susceptible, in the presence of storm and darkness, to impressions that inspire feelings both of dread and anxiety, which by pretended occupations he strives in vain to conceal.^[2] Day and night we now have thunder-storms. The clouds are in continual movement, and the darkened air, laden with vapour, flies in all directions through the skies. The combat which the clouds seem to court and to dread appears to make them more thirsty than ever. They resort to extraordinary means to refresh themselves; in tunnel form, when time and opportunity fail to allow them to quench their thirst from the surrounding atmosphere in the usual manner, they descend near the surface of the sea, and appear to lap the water directly up with their black mouths. Water-spouts thus created are often seen in the changing season, especially among small groups of islands, which appear to facilitate their formation,^[3] The water-spouts are not always accompanied by strong winds; frequently more than one is seen at a time, where-upon the clouds whence they proceed disperse in various directions, and the ends of the water-spouts bending over finally causes them to break in the middle, although the water which is now seen foaming around their base has suffered little or no movement laterally.

705. Water-spouts.—" Yet often the wind prevents the formation of water-spouts. In their stead the wind-spout shoots up like an arrow, and the sea seems to try in vain to keep it back. The sea, lashed into fury, marks with foam the path along which the conflict rages, and roars with the noise of its water-spouts; and woe to the rash mariner who ventures therein!^[4] The height of the spouts is usually somewhat less than 200 yards, and their diameter not more than 20 feet, yet they are often taller and thicker; when the opportunity of correctly measuring them has been favourable, however, as it generally was when they passed between the islands, so that the distance of their bases could be accurately determined, I have never found them higher than 700 yards, nor thicker than 50 yards. In October, in the Archipelago of Rio, they travel from north-west to south-east. They seldom last longer than five minutes; generally they are dissipated in less time. As they are going away, the bulbous tube, which is as palpable as that of a thermometer, becomes broader at the base, and little clouds, like steam from the pipe of a locomotive, are continually thrown off from the circumference of the spout, and gradually the water is released, and the clouds whence the spout came again closes its mouth.^[5]

706. The east monsoon in the Java Sea.—" During the changing of the monsoons, it is mostly calm or cool, with gentle breezes, varied with rain-storms and light gales from all points of the compass. They are harassing to the crew, who, with burning faces under the clouded skies,^[6] impatiently trim the sails to the changing winds. However, the atmosphere generally becomes clear, and, contrary to expectation, the north-east wind comes from a clear sky; about the coming of the monsoon it is northerly. Now the clouds are again packed together; the wind dies away, but it will soon be waked up to come again from another point. Finally, the regular land and sea breezes gradually replace rain, and tempests, calms, and gentle gales. The rain holds up during the day, and in the Java Sea we have the east monsoon. It is then May. Farther to the south than the Java Sea the east monsoon commences in April.^[7] This monsoon prevails till September or October, when it turns to become the west monsoon. It has seemed to me that the east monsoon does not blow the same in every month, that its direction becomes more southerly, and its power greater after it has prevailed for some time.^[8]

707. Currents.—"It is sufficiently important to fix the attention, seeing that these circumstances have great influence upon the winds in the many straits of the Archipelago, in which strong currents run most of the time. Especially in the straits to the east of Java these currents are very strong. I have been unable to stem the current with eight-mile speed. However, they do not always flow equally strong, nor always in the same direction. They are probably the strongest when the tidal current and the equatorial current meet together. It is said that the currents in the straits during the east monsoon run eighteen hours to the north and six hours to the south, and the reverse during the west

monsoon. The passing of the meridian by the moon appears to be the fixed point of time for the turning of the currents. It is probable that the heated water of the Archipelago is discharged to the north during the east monsoon, and to the south during the west monsoon.

708. Marking the seasons.—"As the sea makes the coming of the southern summer known to the inhabitants of the Java coast,^[9] the turning of the east monsoon into the west monsoon commences. After the sun has finished its yearly task in the northern hemisphere, and brings its powerful influence to operate in the southern hemisphere, a change is at once perceived in the constant fine weather of the east monsoon of the Java Sea. As soon as it is at its height upon the Java Sea (6° south), then the true turning of the monsoon begins, and is accomplished much more rapidly than the spring turning. The calms then are not so continuous. The combat in the upper atmosphere appears to be less violent; the south-east trade, which has blown as the east monsoon, does not seem to have sufficient strength to resist the aggressors, who, with wild storms from the north-west and west, make their superiority known. Upon and in the neighbourhood of the land thunder-storms occur, but at sea they are less frequent.

709. Conflicts in the air.—"The atmosphere, alternately clear and cloudy, moves more definitely over from the north-west, so that it appears as if no combat was there waged, and the south-east gives place without a contest. The land breezes become less frequent, and the phenomena by day and night become, in a certain sense, more accordant with each other. Storms of wind and rain beneath a clouded sky alternate with severe gales and steady winds. In the last of November the west monsoon is permanent.

710. Passing of the calm belts.—"Such are the shiftings. But what have they to do with the general system of the circulation of the atmosphere? Whenever we read attentively the beautiful meditations of the founder of the Meteorology of the Sea, and follow him in the development of his hypothesis, which lays open to view the wheels whereby the atmosphere performs its varied and comprehensive task with order and regularity, then it will not be necessary to furnish proof that these turnings are nothing else than the passing of a belt of calms which separates the monsoons from each other, and which, as we know, goes annually with the sun from the south to the north, and back over the torrid zone to and fro.

711. Where they are, there the changing of the monsoons is going on.—" So also the calms, which precede the land and sea winds, are turned back. If, at the coming of the land-wind in the hills, we go with it to the coast—to the sea, we shall perceive that it shoves away the calms which preceded it from the hills to the coast, and so far upon the sea as the land-wind extends. Here, upon the limits of the permanent monsoon, the place for the calms remains for the night, to be turned back to the land and to the hills the following day by the sea-wind. In every place where these calms go, the land and sea-winds turn back. If various observers, placed between the hills and the sea, and between the coast and the farthest limit of the land-wind, noted the moment when they perceived the calms, and that when they perceived the land-wind, then by this means they would learn how broad the belt of calms has been, and with what rapidity they are pushed over the sea and over the land. And even though the results one day should be found not to agree very well with those of another, they would at least obtain an average thereof which would be of value. So, on a larger scale, the belt of calms which separates the monsoons from each other presses in the spring from the south to the north, and in the fall from the north to the south, and changes the monsoons in every place where it presses."^[10]

1. Dr. Buist.
2. No phenomena in nature make a deeper impression upon the sailor than a dark thunder-storm in a calm at sea.—Jansen.
3. I never saw more water-spouts than in the Archipelago of Bioun Singen during the changing. Almost daily we saw one or more.—Jansen.
4. The air-spouts near the equator always appear to mo to be more dangerous than the water-spouts. I have once had one of the latter to pass a ship's length ahead of me, but I perceived little else than a waterfall in which I thought to come, yet no wind. Yet the water-spouts there also are not to be trusted. I have seen such spouts go up out of the water upon the shore, where they overthrew strong isolated frame houses. I have, however, never been in a situation to observe in what direction they revoked,—Jansen.
5. Miniature water-spouts may be produced artificially by means of electricity, and those in nature are supposed to be caused by the display of electrical phenomena. "From the conductor of an electrical machine," says Dr. Bonzano, of New Orleans, "suspend by a wire or chain a small metallic ball (one of wood covered with tinfoil), and under the ball place a rather wide metallic basin containing some oil of turpentine, at the distance of about three-quarters of an inch. If the handle of the machine be now turned slowly, the liquid in the basin will begin to move in different directions, and form whirlpools. As the electricity on the conductor accumulates, the troubled liquid will elevate itself in the centre, and at last become attached to the ball. Draw off the electricity from the conductor to let the liquid resume its position: a portion of the turpentine remains attached to the ball. Turn the handle again very slowly, and observe now the few drops adhering to the ball assume a conical shape, with the apex downward, while the liquid under it assumes also a conical shape, the apex upward, until both meet. As the liquid does not accumulate on the ball, there must necessarily be as great a current downward as upward, giving the column of liquid a rapid circular motion, which continues until the electricity from the conductor is nearly all discharged, silently, or until it is discharged by a spark descending into the liquid. The same phenomena take place with oil or water. Using the latter liquid, the ball must be brought much nearer, or a much greater quantity of electricity is necessary to raise it.

   "If, in this experiment, we let the ball swung to and fro, the little water-spout will travel over its miniature sea, carrying its whirlpools along with it. When it breaks up, a portion of the liquid, and with it anything it may contain, remains attached to the ball. The fish, seeds, leaves, etc., etc., that have fallen to the earth in rain-squalls, may have owed their elevation to the clouds to the same cause that attaches a few drops of the liquid, with its particles of impurities, to the ball."

   "By reference to Plate XIII., we see that the phenomenon of thunder and lightning is of much more frequent occurrence in the North than in the South Atlantic; and I infer that we have more electrical phenomena in the northern than in the southern hemisphere. Do water-spouts occur on one side of the equator more frequently than they do on the other? I have cruised a great deal on the southern hemisphere, and never saw a water-spout there. According to the log-books at the Observatory, they occur mostly on the north side of the equator.—Maury.

6. At sea the face and hands burn (change the skin) much quicker under a clouded than under a clear sky.—Jansen.
7. In the north-east part of the Archipelago the east monsoon is the rainy monsoon. The phenomena in the north-east part are thus wholly different from those in the Java Sea.—Jansen.
8. As is well known, the Strait of Soerabaya forms an elbow whose easterly outlet opens to the east, while the westerly outlet opens to the north. In the beginning of the east monsoon the sea wind (east monsoon) blows through the westerly entrance as far as Grissee (in the elbow); in the latter part of this monsoon, the sea-wind blows, on the contrary, through the easterly entrance as far as Sambilangan (the narrow passage where the westerly outlet opens into the sea).—Jansen.
9. In the Archipelago we have generally high water but once a day, and, with the equinoxes, the tides also turn. The places which have high water by day in one monsoon get it at night in the other.—Jansen.
10. Bijdrage Natuurkündige Beschrijving der zeën, vertaald door M. H. Jansen, Luitenant ter zee.