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 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