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 accumulation 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.