CHAP. XVIII.

Tendence of Meteoric Action in the Atmosphere, as connected with the Annual and Lunar Circle.

BUT the latter is not the only point of view in which these changes of the seasons at the extremity of Hindoostan claim our attention; as by them we are likewise supplied with the most unerring data in reference to one of the most difficult and important departments of meteorology, viz. those which influence and determine the tendencies either to drought or humidity, whether as connected with the annual or lunar circle of meteoric action. Which, it may be added, are of a nature such, as, throughout the year, and in every latitude and species of locality, exercise so marked an influence on the seasons and weather, that without some acquaintance with these the principles to which they are referable,-calculation in regard to expected changes in the weather, would still continue to be, as heretofore, both doubtful and imperfect. And as from the actions in the annual circle being the ground of the actions in the lunar and diurnal, they are those which throughout the year exercise the greatest influence on the seasons and weather; the circumstances which determine the changes in these tendencies in the latter,

are those necessarily which first claim our attention. And as the operation of the causes connected with these changes in the annual circle are sooner felt, and more strongly marked in the weather, in the vicinity of the sites occupied by the main foci of the opposite actions of the sun, in the lower latitudes, and polar regions, than in those which lie between: this brings us to a re-consideration of the principles, under the present point of view, connected with the sudden changes which, at the periods of the equinoxes, take place in the seasons, on the opposite shores of Malabar and Coromandel. These changes, as we perceive, instead of advancing, as elsewhere, by slow and, as it were, imperceptible degrees; being, as described, both sudden and entire. And assuming the cause of these changes, as stated, to consist in the transition which at the equinoxes takes place in the magnetic action of the sun from the pole of the approaching summer, to that of the approaching winter hemisphere of the earth;-the first circumstance to notice, as connected with them is, that the extremes of the lever, to the alternate changes in the action of which they are referable, are not confined to either, but extend to the extremities of these the opposite hemispheres: this lever being no other than the line or meridian which connects their opposite magnetic poles. And which, as the main force or amount of the magnetic action of the sun at each succeeding equinox, becomes alter

nately transferred from one to the other of these poles, of the sudden revolution in the direction of magnetic action throughout the body of the atmosphere, consequent thereon, the violent phenomena which, from these the periods of their occurrence, are called the equinoctial gales, are to be esteemed the first effects; and which subsequently, or after the equilibrium of magnetic action is anew restored in the direction thus given to it ;-and that, with the advance of the season, its force increases in the vicinity of the pole :-as this action continues to weigh on, and sink the temperature in the winter hemisphere, it serves, by its gradual diminution in the opposite, to elevate it in the latter to the same extent. And thus, as from after the autumnal equinox we approach the period of the winter solsticeas being connected with the gradual fall of its temperature, the increasing force of magnetic action in the winter hemisphere, induces a continual tendence in the weather during this period of the year to rain: as, owing to the operation of a totally different principle, viz. the consecutive increase of electric action, the tendence of the weather in the opposite or summer hemisphere during the same interval, is to drought. This necessarily causes that, similar to the seasons, the tendence of meteoric action in the opposite hemispheres of the earth, from the equinoxes to the solstices is constantly contrasted; and that, by means of these the changes of position alter

nately in the magnetic, equally as in the electric action of the sun at the periods of the equinoxes, both at the poles and tropics,—similar to the opposite strokes of the steam-engine connected with its movement of rotation, it is, that the annual revolution of the seasons and weather in both hemispheres, is upheld and perpetuated.

And, as from the union of the electrical and magnetic forces in the atmosphere, there must of necessity exist in its body a common centre, to and from which, with the changes of the seasons, they converge and diverge to their opposite main foci in the opposite hemispheres; and which as being the true limit of meteoric action in either, can be no other, as already noticed, than the magnetic equator by which they are separated. It is easy to see that in these the periodical changes which, at the equinoxes take place in the sites of the main foci of these forces from either hemisphere to the opposite, that as the point of their horizontal collision at these periods, must be on the line of the magnetic equator, that it is on, or in the vicinity of the latter they should first induce those changes in the seasons and weather, incident thereto. And this will serve to show why, as proved by the fact, that, owing to the position and local influence exercised by the chain of mountains which separates the opposite sides of the peninsula of India, it is here where these periodical changes in the opposite actions of the sun first pro

duce their effects on the seasons and weather. And that, as the magnetic equator, or axis of magnetic action, is situated at, or in the vicinity of the line, and is, in those regions, consequently, the weaker action of the sun; conformable to the law in reference to the concentric action of these forces in the atmosphere already stated, viz. that the meteoric action incident thereto always forms on the line described by the axis of the weaker force. Thus, that changes in the weather at the periods of the equinoxes should, in the first instance, as they commence at the junction of the opposite hemispheres, be in their direction east and west. And that as, with the advance of the season, the magnetic action of the sun increased in the winter, as its electric in the opposite or summer hemisphere of the earth; their effects of inducing an increased tendence to rain in the former, as to drought in the latter, should gradually develop themselves further, in the direction of the poles; till, about the periods of the solstices these opposite tendencies on either hand, would have attained their maximum degree, and greatest extension throughout the various regions of both. These the opposite actions of the sun, with the opposite tendencies in the weather which they induce, similar to two waves diverging from a common centre in opposite directions, thus, at the periods of the equinoxes, diverging from the line described by the magnetic equator; and, with the ad