AIR.

The heat of the air is by no means so intense as might be expected in a country occupying the middle of the torrid zone. It is more temperate than in many regions without the tropics, the thermometer, at the most sultry hour, which is about two in the afternoon, generally fluctuating between 82 and 85 degrees. I do not recollect to have ever seen it higher than 86 in the shade, at Fort Marlborough; although at Natal, in lat.i.tude 34 minutes north, it is not unfrequently at 87 and 88 degrees. At sunrise it is usually as low as 70; the sensation of cold however is much greater than this would seem to indicate, as it occasions shivering and a chattering of the teeth; doubtless from the greater relaxation of the body and openness of the pores in that climate; for the same temperature in England would be esteemed a considerable degree of warmth. These observations on the state of the air apply only to the districts near the sea-coast, where, from their comparatively low situation, and the greater compression of the atmosphere, the sun's rays operate more powerfully.

Inland, as the country ascends, the degree of heat decreases rapidly, insomuch that beyond the first range of hills the inhabitants find it expedient to light fires in the morning, and continue them till the day is advanced, for the purpose of warming themselves; a practice unknown in the other parts of the island; and in the journal of Lieutenant Dare's expedition it appears that during one night's halt on the summit of a mountain, in the rainy season, he lost several of his party from the severity of the weather, whilst the thermometer was not lower than 40 degrees. To the cold also they attribute the backwardness in growth of the coconut-tree, which is sometimes twenty or thirty years in coming to perfection, and often fails to produce fruit. Situations are uniformly colder in proportion to their height above the level of the sea, unless where local circ.u.mstances, such as the neighbourhood of sandy plains, contribute to produce a contrary effect; but in Sumatra the coolness of the air is promoted by the quality of the soil, which is clayey, and the constant and strong verdure that prevails, which, by absorbing the sun's rays, prevents the effect of their reflection. The circ.u.mstance of the island being so narrow contributes also to its general temperateness, as wind directly or recently from the sea is seldom possessed of any violent degree of heat, usually acquired in pa.s.sing over large tracts of land in the tropical climates. Frost, snow, and hail I believe to be unknown to the inhabitants. The hill-people in the country of Lampong speak indeed of a peculiar kind of rain that falls there, which some have supposed to be what we call sleet; but the fact is not sufficiently established. The atmosphere is in common more cloudy than in Europe, which is sensibly perceived from the infrequency of clear starlight nights. This may proceed from the greater rarefaction of the air occasioning the clouds to descend lower and become more opaque, or merely from the stronger heat exhaling from the land and sea a thicker and more plentiful vapour. The fog, called kabut by the natives, which is observed to rise every morning among the distant hills, is dense to a surprising degree; the extremities of it, even when near at hand, being perfectly defined; and it seldom is observed to disperse till about three hours after sunrise.

WATERSPOUT.

That extraordinary phenomenon, the waterspout, so well known to and described by navigators, frequently makes its appearance in these parts, and occasionally on sh.o.r.e. I had seen many at sea; but the largest and most distinct (from its proximity) that I had an opportunity of observing, presented itself to me whilst on horseback. I was so near to it that I could perceive what appeared to be an inward gyration, distinct from the volume surrounding it or body of the tube; but am aware that this might have been a deception of sight, and that it was the exterior part which actually revolved--as quiescent bodies seem to persons in quick motion, to recede in a contrary direction. Like other waterspouts it was sometimes perpendicular and sometimes curved, like the pipe of a still-head, its course tending in a direction from Bencoolen Bay across the peninsula on which the English settlement stands; but before it reached the sea on the other side it diminished by degrees, as if from want of the supplies that should be furnished by its proper element, and collected itself into the cloud from which it depended, without any consequent fall of water or destructive effect. The whole operation we may presume to be of the nature of a whirlwind, and the violent ebullition in that part of the sea to which the lower extremity of the tube points to be a corresponding effect to the agitation of the leaves or sand on sh.o.r.e, which in some instances are raised to a vast height; but in the formation of the waterspout the rotatory motion of the wind acts not only upon the surface of the land or sea, but also upon the overhanging cloud, and seems to draw it downwards.

THUNDER AND LIGHTNING.

Thunder and lightning are there so very frequent as scarcely to attract the attention of persons long resident in the country. During the north-west monsoon the explosions are extremely violent; the forked lightning shoots in all directions, and the whole sky seems on fire, whilst the ground is agitated in a degree little inferior to the motion of a slight earthquake. In the south-east monsoon the lightning is more constant, but the coruscations are less fierce or bright, and the thunder is scarcely audible. It would seem that the consequences of these awful meteors are not so fatal there as in Europe, few instances occurring of lives being lost or buildings destroyed by the explosions, although electrical conductors have never been employed. Perhaps the paucity of inhabitants in proportion to the extent of country and the unsubstantial materials of the houses may contribute to this observation. I have seen some trees, however, that have been shattered in Sumatra by the action of lightning.*

(*Footnote. Since the above was written accounts have been received that a magazine at Fort Marlborough, containing four hundred barrels of powder, was fired by lightning and blown up on the 18th of March 1782.)

MONSOONS.

The causes which produce a successive variety of seasons in the parts of the earth without the tropics, having no relation or respect to the region of the torrid zone, a different order takes place there, and the year is distinguished into two divisions, usually called the rainy and dry monsoons or seasons, from the weather peculiar to each. In the several parts of India these monsoons are governed by various particular laws in regard to the time of their commencement, period of duration, circ.u.mstances attending their change, and direction of the prevailing wind according to the nature and situation of the lands and coasts where their influence is felt. The farther peninsula of India, where the kingdom of Siam lies, experiences at the same time the effects of opposite seasons; the western side, in the Bay of Bengal, being exposed for half the year to continual rains, whilst on the eastern side the finest weather is enjoyed; and so on the different coasts of Indostan the monsoons exert their influence alternately; the one remaining serene and undisturbed whilst the other is agitated by storms. Along the coast of Coromandel the change, or breaking up of the monsoon as it is called, is frequently attended with the most violent gales of wind.

On the west coast of Sumatra, southward of the equinoctial, the south-east monsoon or dry season begins about May and slackens in September: the north-west monsoon begins about November, and the hard rains cease about March. The monsoons for the most part commence and leave off gradually there; the months of April and May, October and November generally affording weather and winds variable and uncertain.

CAUSE OF THE MONSOONS.

The causes of these periodical winds have been investigated by several able naturalists, whose systems, however, do not entirely correspond either in the principles laid down or in their application to the effects known to be produced in different parts of the globe. I shall summarily mention what appear to be the most evident, or probable at least, among the general laws, or inferences, which have been deduced from the examination of this subject. If the sea were perfectly uninterrupted and free from the irregular influence of lands, a perpetual easterly wind would prevail in all that s.p.a.ce comprehended between the twenty-eighth or thirteenth degrees of north and south lat.i.tude. This is primarily occasioned by the diurnal revolution of the earth upon its axis from west to east; but whether through the operation of the sun, proceeding westward, upon the atmospheric fluid, or the rapidity of revolution of the solid body, which leaves behind it that fluid with which it is surrounded, and thereby causes it virtually to recede in a contrary direction; or whether these principles cooperate, or unequally oppose each other, as has been ingeniously contended, I shall not take upon me to decide. It is sufficient to say that such an effect appears to be the first general law of the tropical winds. Whatever may be the degree of the sun's influence upon the atmosphere in his transient diurnal course, it cannot be doubted but that, in regard to his station in the path of the ecliptic, his power is considerable. Towards that region of the air which is rarefied by the more immediate presence of the heat, the colder and denser parts will naturally flow. Consequently from about, and a few degrees beyond, the tropics, on either side, the air tends towards the equator; and, combining with the general eastern current before mentioned, produces (or would, if the surface were uniform) a north-east wind in the northern division, and a south-east in the southern; varying in the extent of its course as the sun happens to be more or less remote at the time. These are denominated the trade-winds, and are the subject of the second general observation. It is evident that, with respect to the middle s.p.a.ce between the tropics, those parts which at one season of the year lie to the northward of the sun, are, during another, to the southward of him; and of course that an alteration of the effects last described must take place, according to the relative situation of the luminary; or in other words, that the principle which causes at one time a north-east wind to prevail at any particular spot in those lat.i.tudes must, when the circ.u.mstances are changed, occasion a south-east wind.

Such may be esteemed the outline of the periodical winds, which undoubtedly depend upon the alternate course of the sun northwards and southwards; and this I state as the third general law. But although this may be conformable with experience in extensive oceans, yet, in the vicinity of continents and great islands, deviations are remarked that almost seem to overturn the principle. Along the western coast of Africa and in some parts of the Indian seas, the periodical winds, or monsoons as they are termed in the latter, blow from the west-north-west and south-west, according to the situation, extent, and nature of the nearest lands; the effect of which upon the inc.u.mbent atmosphere, when heated by the sun at those seasons in which he is vertical, is prodigious, and possibly superior to that of any other cause which contributes to the production or direction of wind. To trace the operation of this irregular principle through the several winds prevalent in India, and their periodical failures and changes, would prove an intricate but, I conceive, by no means an impossible task.* It is foreign however to my present purpose, and I shall only observe that the north-east monsoon is changed, on the western coast of Sumatra, to north-west or west-north-west by the influence of the land. During the south-east monsoon the wind is found to blow there, between that point and south.

Whilst the sun continues near the equator the winds are variable, nor is their direction fixed till he has advanced several degrees towards the tropic: and this is the cause of the monsoons usually setting in, as I have observed, about May and November, instead of the equinoctial months.

(*Footnote. It has been attempted, and with much ingenious reasoning, by Mr. Semeyns in the third volume of the Haerlem Transactions which have but lately fallen into my hands.)

LAND AND SEA BREEZES.

Thus much is sufficient with regard to the periodical winds. I shall proceed to give an account of those distinguished by the appellation of land and sea breezes, which require from me a minuter investigation, both because, as being more local, they more especially belong to my subject, and that their nature has. .h.i.therto been less particularly treated of by naturalists.

In this island, as well as all other countries between the tropics of any considerable extent, the wind uniformly blows from the sea to the land for a certain number of hours in the four and twenty, and then changes and blows for about as many from the land to the sea; excepting only when the monsoon rages with remarkable violence, and even at such time the wind rarely fails to incline a few points, in compliance with the efforts of the subordinate clause, which has not power, under these circ.u.mstances, to produce an entire change. On the west coast of Sumatra the sea-breeze usually sets in, after an hour or two of calm, about ten in the forenoon, and continues till near six in the evening. About seven the land-breeze comes off, and prevails through the night till towards eight in the morning, when it gradually dies away.

CAUSE OF THE LAND AND SEA-BREEZES.

These depend upon the same general principle that causes and regulates all other wind. Heat acting upon air rarefies it, by which it becomes specifically lighter, and mounts upward. The denser parts of the atmosphere which surround that so rarefied, rush into the vacuity from their superior weight; endeavouring, as the laws of gravity require, to restore the equilibrium. Thus in the round buildings where the manufactory of gla.s.s is carried on, the heat of the furnace in the centre being intense, a violent current of air may be perceived to force its way in, through doors or crevices, on opposite sides of the house. As the general winds are caused by the DIRECT influence of the sun's rays upon the atmosphere, that particular deviation of the current distinguished by the name of land and sea breezes is caused by the influence of his REFLECTED rays, returned from the earth or sea on which they strike. The surface of the earth is more suddenly heated by the rays of the sun than that of the sea, from its greater density and state of rest; consequently it reflects those rays sooner and with more power: but, owing also to its density, the heat is more superficial than that imbibed by the sea, which becomes more intimately warmed by its transparency and by its motion, continually presenting a fresh surface to the sun. I shall now endeavour to apply these principles. By the time the rising sun has ascended to the height of thirty or forty degrees above the horizon the earth has acquired, and reflected on the body of air situated over it, a degree of heat sufficient to rarefy it and destroy its equilibrium; in consequence of which the body of air above the sea, not being equally, or scarcely at all, rarefied, rushes towards the land and the same causes operating so long as the sun continues above the horizon, a constant sea-breeze, or current of air from sea to land, prevails during that time. From about an hour before sunset the surface of the earth begins to lose the heat it has acquired from the more perpendicular rays. That influence of course ceases, and a calm succeeds. The warmth imparted to the sea, not so violent as that of the land but more deeply imbibed, and consequently more permanent, now acts in turn, and by the rarefaction it causes draws towards its region the land air, grown cooler, more dense, and heavier, which continues thus to flow back till the earth, by a renovation of its heat in the morning, once more obtains the ascendancy. Such is the general rule, conformable with experience, and founded, as it seems to me, in the laws of motion and the nature of things. The following observations will serve to corroborate what I have advanced, and to throw additional light on the subject for the information and guidance of any future investigator.

The periodical winds which are supposed to blow during six months from the north-west and as many from the south-east rarely observe this regularity, except in the very heart of the monsoon; inclining, almost at all times, several points to seaward, and not unfrequently blowing from the south-west or in a line perpendicular to the coast. This must be attributed to the influence of that principle which causes the land and sea winds proving on these occasions more powerful than the principle of the periodical winds; which two seem here to act at right angles with each other; and as the influence of either is prevalent the winds draw towards a course perpendicular to or parallel with the line of the coast.

Excepting when a squall or other sudden alteration of weather, to which these climates are particularly liable, produces an irregularity, the tendency of the land-wind at night has almost ever a correspondence with the sea-wind of the preceding or following day; not blowing in a direction immediately opposite to it (which would be the case if the former were, as some writers have supposed, merely the effect of the acc.u.mulation and redundance of the latter, without any positive cause) but forming an equal and contiguous angle, of which the coast is the common side. Thus, if the coast be conceived to run north and south, the same influence, or combination of influences, which produces a sea-wind at north-west produces a land-wind at north-east; or adapting the case to Sumatra, which lies north-west and south-east, a sea-wind at south is preceded or followed by a land-wind at east. This remark must not be taken in too strict a sense, but only as the result of general observation. If the land-wind, in the course of the night, should draw round from east to north it would be looked upon as an infallible prognostic of a west or north-west wind the next day. On this principle it is that the natives foretell the direction of the wind by the noise of the surf at night, which if heard from the northward is esteemed the forerunner of a northerly wind, and vice versa. The quarter from which the noise is heard depends upon the course of the land-wind, which brings the sound with it, and drowns it to leeward--the land-wind has a correspondence with the next day's sea-wind--and thus the divination is accounted for.

The effect of the sea-wind is not perceived to the distance of more than three or four leagues from the sh.o.r.e in common, and for the most part it is fainter in proportion to the distance. When it first sets in it does not commence at the remoter extremity of its limits but very near the sh.o.r.e, and gradually extends itself farther to sea, as the day advances; probably taking the longer or shorter course as the day is more or less hot. I have frequently observed the sails of ships at the distance of four, six, or eight miles, quite becalmed, whilst a fresh sea-breeze was at the time blowing upon the sh.o.r.e. In an hour afterwards they have felt its effect.*

(*Footnote. This observation as well as many others I have made on the subject I find corroborated in the Treatise before quoted from the Haerlem Transactions which I had not seen when the present work was first published.)

Pa.s.sing along the beach about six o'clock in the evening when the sea-breeze is making its final efforts, I have perceived it to blow with a considerable degree of warmth, owing to the heat the sea had by that time acquired, which would soon begin to divert the current of air towards it when it had first overcome the vis inertiae that preserves motion in a body after the impelling power has ceased to operate. I have likewise been sensible of a degree of warmth on pa.s.sing, within two hours after sunset, to leeward of a lake of fresh water; which proves the a.s.sertion of water imbibing a more permanent heat than earth. In the daytime the breeze would be rendered cool in crossing the same lake.

Approaching an island situated at a distance from any other land, I was struck with the appearance of the clouds about nine in the morning which then formed a perfect circle round it, the middle being a clear azure, and resembled what the painters call a glory. This I account for from the reflected rays of the sun rarefying the atmosphere immediately over the island, and equally in all parts, which caused a conflux of the neighbouring air, and with in the circ.u.mjacent clouds. These last, tending uniformly to the centre, compressed each other at a certain distance from it, and, like the stones in an arch of masonry, prevented each other's nearer approach. That island, however, does not experience the vicissitude of land and sea breezes, being too small, and too lofty, and situated in a lat.i.tude where the trade or perpetual winds prevail in their utmost force. In sandy countries, the effect of the sun's rays penetrating deeply, a more permanent heat is produced, the consequence of which should be the longer continuance of the sea-breeze in the evening; and agreeably to this supposition I have been informed that on the coast of Coromandel it seldom dies away before ten at night. I shall only add on this subject that the land-wind on Sumatra is cold, chilly, and damp; an exposure to it is therefore dangerous to the health, and sleeping in it almost certain death.

SOIL.

The soil of the western side of Sumatra may be spoken of generally as a stiff, reddish clay, covered with a stratum or layer of black mould, of no considerable depth. From this there springs a strong and perpetual verdure of rank gra.s.s, brushwood, or timber-trees, according as the country has remained a longer or shorter time undisturbed by the consequences of population, which, being in most places extremely thin, it follows that a great proportion of the island, and especially to the southward, is an impervious forest.

UNEVENNESS OF SURFACE.

Along the western coast of the island the low country, or s.p.a.ce of land which extends from the seash.o.r.e to the foot of the mountains, is intersected and rendered uneven to a surprising degree by swamps whose irregular and winding course may in some places be traced in a continual chain for many miles till they discharge themselves either into the sea, some neighbouring lake, or the fens that are so commonly found near the banks of the larger rivers and receive their overflowings in the rainy monsoons. The spots of land which these swamps encompa.s.s become so many islands and peninsulas, sometimes flat at top, and often mere ridges; having in some places a gentle declivity, and in others descending almost perpendicularly to the depth of a hundred feet. In few parts of the country of Bencoolen, or of the northern districts adjacent to it, could a tolerably level s.p.a.ce of four hundred yards square be marked out. I have often, from an elevated situation, where a wider range was subjected to the eye, surveyed with admiration the uncommon face which nature a.s.sumes, and made inquiries and attended to conjectures on the causes of these inequalities. Some choose to attribute them to the successive concussions of earthquakes through a course of centuries. But they do not seem to be the effect of such a cause. There are no abrupt fissures; the hollows and swellings are for the most part smooth and regularly sloping so as to exhibit not unfrequently the appearance of an amphitheatre, and they are clothed with verdure from the summit to the edge of the swamp.

From this latter circ.u.mstance it is also evident that they are not, as others suppose, occasioned by the falls of heavy rains that deluge the country for one half of the year; which is likewise to be inferred from many of them having no apparent outlet and commencing where no torrent could be conceived to operate. The most summary way of accounting for this extraordinary unevenness of surface were to conclude that, in the original construction of our globe, Sumatra was thus formed by the same hand which spread out the sandy plains of Arabia, and raised up the alps and Andes beyond the region of the clouds. But this is a mode of solution which, if generally adopted, would become an insuperable bar to all progress in natural knowledge by damping curiosity and restraining research. Nature, we know from sufficient experience, is not only turned from her original course by the industry of man, but also sometimes checks and crosses her own career. What has happened in some instances it is not unfair to suppose may happen in others; nor is it presumption to trace the intermediate causes of events which are themselves derived from one first, universal, and eternal principle.

CAUSES OF THIS INEQUALITY.

To me it would seem that the springs of water with which these parts of the island abound in an uncommon degree operate directly, though obscurely, to the producing this irregularity of the surface of the earth. They derive their number and an extraordinary portion of activity from the loftiness of the ranges of mountains that occupy the interior country, and intercept and collect the floating vapours. Precipitated into rain at such a hight, the water acquires in its descent through the fissures or pores of these mountains a considerable force which exerts itself in every direction, lateral and perpendicular, to procure a vent.

The existence of these copious springs is proved in the facility with which wells are everywhere sunk; requiring no choice of ground but as it may respect the convenience of the proprietor; all situations, whether high or low, being prodigal of this valuable element. Where the approaches of the sea have rendered the cliffs abrupt, innumerable rills, or rather a continued moisture, is seen to ooze through and trickle down the steep. Where on the contrary the sea has retired and thrown up banks of sand in its retreat I have remarked the streams of water, at a certain level and commonly between the boundaries of the tide, effecting their pa.s.sage through the loose and feeble barrier opposed to them. In short, every part of the low country is pregnant with springs that labour for the birth; and these continual struggles, this violent activity of subterraneous waters, must gradually undermine the plains above. The earth is imperceptibly excavated, the surface settles in, and hence the inequalities we speak of. The operation is slow but unremitting, and, I conceive, fully capable of the effect.

MINERAL PRODUCTIONS.

The earth of Sumatra is rich in minerals and other fossil productions.

GOLD.

No country has been more famous in all ages for gold, and, though the sources from whence it is drawn may be supposed in some measure exhausted by the avarice and industry of ages, yet at this day the quant.i.ty procured is very considerable, and doubtless might be much increased were the simple labour of the gatherer a.s.sisted by a knowledge of the arts of mineralogy.

COPPER, IRON, TIN, SULPHUR.

There are also mines of copper, iron, and tin. Sulphur is gathered in large quant.i.ties about the numerous volcanoes.

SALTPETRE.

Saltpetre the natives procure by a process of their own from the earth which is found impregnated with it; chiefly in extensive caves that have been, from the beginning of time, the haunt of a certain species of birds, of whose dung the soil is formed.

COAL.

Coal, mostly washed down by the floods, is collected in several parts, particularly at Kataun, Ayer-rammi, and Bencoolen. It is light and not esteemed very good; but I am informed that this is the case with all coal found near the surface of the earth, and, as the veins are observed to run in an inclined direction until the pits have some depth, the fossil must be of an indifferent quality. The little island of Pisang, near the foot of Mount Pugong, was supposed to be chiefly a bed of rock crystal, but upon examination of specimens taken from thence they proved to be calcareous spar.

HOT SPRINGS.

Mineral and hot springs have been discovered in many districts. In taste the waters mostly resemble those of Harrowgate, being nauseous to the palate.

EARTH OIL.

The oleum terrae, or earth oil, used chiefly as a preservative against the destructive ravages of the white-ants, is collected at Ipu and elsewhere.*

(*Footnote. The fountain of Naphtha or liquid balsam found at Pedir, so much celebrated by the Portuguese writers, is doubtless this oleum terrae, or meniak tanah, as it is called by the Malays.)

SOFT ROCK.

There is scarcely any species of hard rock to be met with in the low parts of the island near the seash.o.r.e. Besides the ledges of coral, which are covered by the tide, that which generally prevails is the napal, as it is called by the inhabitants, forming the basis of the red cliffs, and not infrequently the beds of the rivers. Though this napal has the appearance of rock it possesses in fact so little solidity that it is difficult to p.r.o.nounce whether it be a soft stone or only an indurated clay. The surface of it becomes smooth and glossy by a slight attrition, and to the touch resembles soap, which is its most striking characteristic; but it is not soluble in water and makes no effervescence with acids. Its colour is either grey, brown, or red, according to the nature of the earth that prevails in its composition. The red napal has by much the smallest proportion of sand, and seems to possess all the qualities of the steat.i.te or soap-earth found in Cornwall and other countries. The specimens of stone which I brought from the hills in the neighbourhood of Bencoolen were p.r.o.nounced by some mineralogists, to whom I showed them at the time, to be granite; but upon more particular examination they appear to be a species of trap, consisting princ.i.p.ally of feldspar and hornblende, of a greyish colour and nearly similar to the mountain stone of North Wales.

PETRIFACTION.