fined, not only because they extend a during the summer than the winter mc because the strength of the constant w declines as you approach to their utmost that the variable winds sometimes encro the usual region of the trade winds, a these last prevail over the former for a neral, the trade winds are found to p low latitudes, within the 30th degree, the equator; all beyond which latitude sidered as the region of variable winds.

But though the winds may be called st tain within the tropics, they are by no m able. In certain regions they fhift at st and in others they are susceptible of pe tions, while in other parts of these regi tinue immutably the same. Philosoph tinguished these various winds by diff Wherever they are immutable they have in English, the general trade winds. fhift regularly twice a year, have been winds also, from the uses that are made they are more particularly denominated m other regular variable winds within the t of a more local nature, have each obtaine lar name in those regions where they parti vail. It is proposed for the present only tice of the two first.

of the general trade winds.

The general trade wind prevails in all those large oceans that are unincumbered with land for a considerable distance on either side the equator. Hence they reign invariably throughout the whole great South Sea, and the Atlantic Ocean on both sides the equator, and in the Indian Ocean, with little exception to the south of the line. In all those places, in fhort, which are marked on the map with single darts, the wind always blowing towards that quarter to which the point of the darts are turned throughout the whole year.

It has been already said that these winds are occasioned by the heat of the sun in equatorial regions, where his rays acting perpendicularly on the earth's surface, are reflected with greater force, and heat the air, upon the whole, to a greater degree, and rarifie it more, and consequently render it lighter there than on any other part of the globe. In consequence of this expansion, the denser air, in higher latitudes, flows necefsarily towards the equator, from either side of the globe. This, if not affected by other circumstances, would produce a direct northerly wind in the northern, and a southerly wind in the southern hemispheres; but as the direct influence of the sun is constantly shifting over the earth's surface, from east to west, in consequence of the earth's diurnal motion, an easterly wind, if this influence alone were to operate, would thus be produced. From these two causes operating at the same time, the trade winds naturally blow from the N. E. on the north,

that the point towards which these wi not be invariably the same throughout t but that it will vary a little in different proaching nearer the tropic of Cancer du mer, and inclining more to that of Capric This is so obvious as to require only mentioned.

Of monsoons.

The monsoons are a variation of the winds, which prevail only in certain plac tropics. They blow, in general, nearly in one direction, and then, after a fhort in riable and stormy weather, they chang for nearly other six months in a direction posite to their former course. This vari trade wind is found to take place in all Indian ocean, to the north of the line, and straits of Malacca, as far as the island o on the Chinese coast, and among the is southward of that. Monsoons also pre small distance to the south of the equator, islands stretching from the straits of Malac New Holland as may be seen in the map, the monsoons are denoted by double dar where else in the southern hemisphere.

The causes of the general trade winds long known, and distinctly explained in man phical treatises; but the cause of the mon

not been so generally understood, though it constitutes a very material link in the physical knowledge of the globe.

It is hoped the following explanation of them will be found satisfactory.

The reader will please to recollect, that the sea and land breezes which are so beneficial in all tropical regions, are a temporary interruption, for a small extent only, of the general trade wind. It has been fhewn (vol. vi. p. ) that these are occasioned by the great variation that takes place between the heat of the day, and the coolness of night in tropical regions.

Our philosophical pupils will also recollect, that in consequence of the inclination of the earth's axis to the plane of the ecliptic, conjoined with its annual and diurnal rotations, it so happens that the length of the day must be invariably the same at the equator, throughout the whole year; but that, on every other part of the surface of the globe, the length of the day is perpetually varying, so as to produce that diversity of seasons which we call summer and winter; and that the difference between the longest and fhortest day in any place goes on continually increasing with its latitude from the equator, till you reach the pole, where the whole heat of the year is concentrated into one day of six months duration, which we call summer, and all the cold is accumulated into one night of six months, called winter, without any sensible interruption of either the heat or the cold, in these regions, in consequence of the diurnal rotation of the earth.

Hence it follows, that at the equator the great vicifsitudes of heat and cold are occasioned by the diur

nal rotation of the globe, and produce their sensible effects by the changes that take place between the day and the night, where is, in polar regions, the great vicifsitudes of heat and cold are occasioned by the earth's annual revolution, and produce their sensible * effects by the changes that take place between the summer and the winter. Hence again it follows, that if the heat of the sun were the only cause of the variation of winds, the changes, if any, that were produced by that means, in equatorial regions, ought to be diurnal only, whereas the vicifsitudes at the pole fhould be only experienced once in six months.

And, as these deviations of climate and seasons are gradual from the equator to the poles, it must happen that as you approach to, or recede from either the one or the other of these vicifsitudes will be more or less experienced. But at the equator, the influence of the sun is more powerful, upon the whole, than at the pole. The effects of the sun, therefore, in altering the wind, must be much less interrupted by lefser causes, and therefore more steady in equatorial than in polar regions, and consequently must be much more stricking to the senses.

Experience, in this instance, accords exactly with our reasoning. Variable winds do, in general, prevail towards the poles, and constant winds towards the equator. But, in summer, the continual heat, even in high latitudes, comes to be sensibly felt, and produces changes on the wind that are distinctly perceptible. In our own cold region, the effects of the sun on the winds are sensibly felt during summer and autumn, though much inferior in degree to that in