LECTURE XVI.

WINDS.

I SHALL now touch upon the winds and their causes. The winter is past, and the voice of the singing-bird is again heard in our land. The sun has ascended his chariot of light. The stars have fled, and the morning mists are rolled away from his course, like the raising of a magnificent curtain. The flowers exhale their odours, as they shake off their pearly drops. The lark soars and sings. Nature, coming out of her chambers of darkness, resumes her vivid colours and her freshness. Man springs from sleep to enjoy this renovated existence, and goes forth to his labour in the fields.

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At this moment a gentle breeze precedes the chariot of the sun. You may cry with Archimedes, that you have found the great secret - that have divined the origin of the winds. The gentle zephyr which breezes from the east, is air-dilated and rarefied by the first rays of the sun, extending itself by its elasticity. The cooler air rushes in to supply the vacuum. Such is the cause of the trade

winds of the torrid zone.

The warmth of the sun acting upon the air, so extremely easy to rarefy, condense, or expand, is the first and prominent cause of the winds. This orb, in pursuing its sublime path, and heating the masses of air under its course in the torrid zone, produces those regular breezes called the trade winds. Astonishing wisdom and beneficence of Providence, which, in that very culminating fierceness of the sun's rays that would render the climate uninhabitable, has provided a remedy for the heat in a steady, cool, and refreshing breeze, which fans the burning rays that create it! What a spectacle would the blue expanse above us ex

hibit, if the air was visible! We should see the atmosphere rolling in waves, as much more impetuous than those of the sea, as air is lighter than water. What fearful omens in the discoloured miasms, and the seeds of pestilence walking in darkness, disclosed to the eye in its gloomy tinge of combination with the atmosphere! The simple apparatus of a flask will enable me to show you some of the more

striking properties of the air. You are aware that the heroes of Homer were enabled to procure, of the god of the winds, certain bags of that element for their individual use. Virgil represents the winds as prisoners caged in a cave, and I hope to show you the causes of the wind at the bottom of a flask of glass. Why not? Has not Don Cleophas, in his 'diable boiteux,' presented the most amiable of demons corked up in a bottle? Has not Rabelais assured us, that Panurge found truth in a bottle? In the same vessel I hope to show you the cause of the winds.

I present a close corked flask to the action of heat. Scarcely has the air contained in the bottle begun to feel the influence of the rarefaction, before the flask bursts into a thousand pieces. Judge by the action of heat upon the air contained in this small vessel, what force the expansion of the air must have, when dilated by the action of that vast burning planet, the sun, a million times larger than the earth! Do not conclude, however, from this experiment, that the expansion of a part of the atmosphere is the entire cause of the winds. Nature has a thousand expedients to obtain the same result, while the student has but one head to study them. Some philosophers affirm, and it seems to me with reason, that the action of the sun and moon must produce a flux and reflux of tides in the air, as certainly as in the abysses of the ocean. Electric clouds are a prolific

source of winds. We all feel the cool streams of air flowing towards the electric machine in motion. We have seen the terrible impulse of thunder-clouds upon the winds, and have felt the refreshing coolness which succeeds such storms, the grand ventilators of the atmosphere. When the mass of air which circulates over our heads is rarefied by any cause,

the atmosphere at the point of rarefaction becomes sensibly lighter. The wind rushes towards that point. Observe the reason, why we expect a storm when the barometer falls. Though all the elements that concur to form whirlwinds, tornadoes, and hurricanes, may never be detected by the sage, we can see, in the heat of the sun, the play of electric clouds, the unequal distribution of heat and cold in the different zones and climates, and the perpetually changing temperature of mountains, sufficient causes for all degrees of wind, from the zephyr to the hurricane. Even these last terrible phenomena may occur to perform an immense lustration of the atmosphere, purifying it from the seeds of disease and death. For example, the city of Cesi, in Italy, is built upon the declivity of a mountain, through the opening of which breezes a cool and refreshing wind. Yet this breeze is felt only in the summer between morning and evening, and is even proportioned to the heat of the day. The little town of Nyon, in Languedoc, arises in the midst of a fertile valley covered with olives. A river and many small streams wind through it, diffusing life and coolness in their course. Nature seems thus to have provided a remedy for the parching influence of the sun's rays, which, concentrating in this narrow basinshaped vale, incessantly threaten to burn up the harvest. But the streams and trees are not enough. She has placed, upon the summit of the mountain above, a grotto, from which there escapes every morning a fresh and light breeze, which tempers the warmth and fertilizes the fields. During the revolution, the people became wise enough to imagine that they could correct Nature, and they stopped up this grotto. Nature resented their ignorant rashness, by scorching the olive-trees and burning up the harvest. Aware of their outrage upon this wise and beneficent mother, who is never offended with impunity, they demolished their wall, and supplicated from the grotto its fresh breezes. The valley resumed its verdure, and harvest its abundance.

The most brilliant spectacles of nature are due to the air. It is in the air, that the clouds are formed, with their cerulean, brazen, and rosy tints. At one time they are coursers cover

ed with gauzy veils, bringing us tidings along the sky from the sweet south. It is there, the magazines of thunder put forth their terrific power. It is thence, that Aurora makes her triumphal entry; and thence, that, in cloud-canopied grandeur, the sun departs to visit another hemisphere. This is the field of rains and tempests, and equally of dews and the light. The rains fall, the dews are condensed, and the streams are volatilized into vapour, and carried back to their sources on the wings of the wind. The greater portion of that order of the universe, most essential to us, comes from this invisible fluid which surrounds our globe, and follows its movements in its revolutions. What a spectacle would the world exhibit without it! Sometimes a fleet zephyr, it plays upon the turf, waves the young harvest, caresses the flowers, and sighs in the groves. Sometimes an impetuous wind, it sweeps along the sky, shakes the summit of the forests, and mingles its sublime voice with the roar of thunder and the resounding billows.

But the winds play a still more important part in the phenomena of nature. Charged with vapor from the surface of the ocean, they traverse the spaces of the sky, driving the clouds before them; and, as the provident purveyors of the world, scatter verdure and harvests in their course. Stifling heats threaten the plains of the torrid zone; and providence forthwith sends the breezes to fan the burning atmosphere.

We can never too much admire the equality, with which the wind distributes clouds, dews and rains. It seems to measure the waters for each climate, each plain and garden.

Again, rains scarcely ever fall in Egypt. From the earliest dawn of spring, this climate is under the scorching

power of the sun. Verdure dries up. The flowers hang

languid on their stems, and the parched earth seems to invoke the beneficent supplies of water. On a sudden steady winds begin to sweep the atmosphere; and for a whole month bear clouds without rain onwards to the elevated summits of On the vast ranges of mountains in Nubia and Abyssinia. these tempest-beaten summits the clouds do not distil gentle

rains, but burst, and pour down torrents, mingling their roar with the crashes of thunder. The swollen mountain streams, the lakes and reservoirs pour their waters into the Nile. The fertile vale of Lower Egypt is entirely inundated, and the inhabitants traverse their fields, and glide among their palm trees in skiffs; while in the kingdom of Gojam, where the overflow received its supplies, and where the inundation would be useless, it flows tranquilly onwards amidst groves and meadows confined to its bed.

You will ask me, perhaps, why providence has departed from its general economy to water Egypt in this remarkable way? Unbelievers would have the country supplied with water by the same showers that feed the fountains of the Nile. Could human foresight have divined, that rains would raise mortal miasms from these burning plains, which are neutralized, and swallowed up by the turbid waters of the Nile? This observation is founded upon experience. For, if by an extraordinary cause, it happens to rain along the plains of Lower Egypt, epidemic maladies, fever and plague, immediately ensue. But, as soon as the banks of the Nile are inundated, the plague disappears. The change wrought in the air is so sudden that the ravages of death are suspended in the same proportion as the waters rise. Providence, foreseeing that rain would be noxious to Egypt, instructed the winds to guide the vapors and clouds towards the mountains of Nubia and Abyssinia.

It requires about eight minutes for light to come from the sun. But what is that light which presents to us the admirable spectacle of the universe? The thunder rolls; man hears, directs, and even imitates it. But what is the cause of thunder storms? The wind blows; its rapidity is measured. Invisible as it is, its elements are discovered. Even its power becomes subservient to human genius. It swells our sails upon the abysses of the ocean; and yet its cause remains unknown. Amidst this mass of inexplicable natural phenomena, scarcely are a few philosophers able to conjecture the causes of things.