the air at one time, warming and moderating the rigours of climate at another; as cloud, shielding the earth from the scorching sun, checking excessive radiation, and tempering electric influences; as rain, washing impurity from the air and reviving the thirsty soil; as surface moisture, carrying nourishment to plants; as streams, irrigating and fertilising the land; as mineral springs, infusing health into many a shattered frame; and lastly as rivers, bearing along on their deep currents the commerce that multiplies the comforts of life. In every form and stage God has chosen water as His servant to scatter good gifts among His creatures.

Ocean, clouds, rain, and rivers are the elements of a circulation on which the life of the world depends. The ocean is the mighty heart-the clouds and vapours driven by the wind are the distributing arteries-the minute rain-streamlets are the capillaries vivifying every corner of the earth-while the tiny rills, soon swelling into brooks and then into rivers, are the returning veins which empty the water back into the mighty heart. Water is the blood of the earth; where it falls, the surface is living and fruitful; where it is denied, the ground withers into sand. Without the ocean there would be no rain; without rain, no fertile land; without fertile land, no plants;-and without plants no animals.

He gathereth the waters of the sea together, as it were upon an heap; and layeth up the deep as in a treasure-house. Ps. xxxiii.

THE WINDS OF GOD.

O ye Winds of God, bless ye the Lord: praise Him, and magnify Him for ever.

NE cannot bestow a thought on the machinery by which the grandest operations of nature are carried on without perceiving how much is accomplished by means of air and water. In one shape or another these busy agents meet us at every turn ;—sometimes acting singly, sometimes in combination, but always playing into each other's hands with a perfection which one might fancy was the result of a living intelligence, and which nothing short of infinite wisdom could have devised. Animated by solar heat they form the mightiest engines in nature's workshop-labouring with unerring instinct, fetching and carrying, fertilising, vivifying, and supporting life. They form, as it were, the right hand of Providence, and their appointed task is to distribute blessings over the world.

Winds range through an atmosphere encircling our globe to a height of forty-five or fifty miles, and the thickness of this belt in relation to the diameter of the earth has been compared by Maury to the down upon a peach. As air is a fluid, we may consider the atmosphere in its

totality as a gaseous ocean, at the bottom of which we living creatures exist and move about. The upper surface of this ocean obeys the law of gravitation, by which all fluids are compelled to maintain their level; and hence, when accumulations of air arise upon its surface from internal disturbance, they must, like the waves of the sea, flow down upon the lower levels around, until the equilibrium is restored. The air varies in its density at different heights, according to the pressure of the mass above it. It is greatest, therefore, in low situations, as at the level of the sea, where it weighs fifteen pounds to the square inch, or nearly one ton to the square foot. In ascending, the weight of the aerial column diminishes in a nearly fixed ratio, so that by ascertaining its amount by means of a barometer, the altitude of any given spot may be pretty accurately determined. So rapidly does the weight diminish that, at the top of Mont Blanc for example, no less than one half of the total mass of the atmosphere is found to have been left below.

One chief cause of the varying atmospheric weight at the same level is the greater or less abundance of aqueous vapour present in it. Dry air is 60 per cent. heavier than vapour, and consequently when vapour takes the place of a portion of air the weight of the atmospheric column is diminished. This may be illustrated by filling a tea-cup to the brim with water to represent a column of atmosphere. Our position as mortals upon earth is, of course, at the bottom of the cup where the tea-grounds lie; but for the moment we may suppose ourselves looking down upon the top of the atmosphere represented by the surface of the full cup. If we now displace a portion of the water by pouring in some lighter fluid, as spirits of wine, the weight of the column will be necessarily diminished; for the tea-cup, instead of being completely filled as before with the denser fluid, will be partly filled with

the lighter fluid also. In a corresponding ratio the weight upon the bottom of the cup, representing the surface of the earth, will be lightened. There can be no permanent accumulation on the top, for the excess of fluid runs over upon the surrounding lower levels, like a sea wave, and thus the same height is always maintained. In a general way, therefore, a low state of the barometer indicates a light or vaporous condition of the atmosphere and a disturbance in the aerial equilibrium; hence, rain and wind are to be expected. How many there are who habitually pass by the little instrument as it hangs in its corner in the Hall without a thought of gratitude or of admiration at the wonderful series of adjustments on which its signals are founded. How different it is at sea! There the mariner consults it often and anxiously, as he would a truthful friend who can point out to him betimes when danger threatens. Every movement is analysed, its slightest hints are carefully pondered. Never does a day pass by on which lives are not saved by the warning throbs of this atmospheric pulse.

To be "as fickle as the wind" is one of those proverbial reproaches which are sometimes made with scant justice at nature's expense. In reality, however, the laws of the winds are as fixed as other physical laws, only, from the difficulty of tracing their action in the aerial regions where they rule, we are as yet in the infancy of our knowledge respecting them. In Ecclesiastes we read, "The wind goeth toward the south, and turneth about unto the north; it whirleth about continually, and the wind returneth again according to his circuits." This is one of those profound expressions in physical science sometimes met with in the sacred volume, which, though greatly in advance of the knowledge prevailing at the time when they were written, have been confirmed with literal exactness by modern investigation. We have

here, indeed, the pith of all that is known in regard to atmospheric circulation, and it could hardly be more clearly or beautifully stated. The grand circuit of the wind is from the poles to the equator and back again in unceasing rounds; at one time, sweeping broadly across the surface of the earth; at another, passing in vast volumes in a contrary direction in the upper regions of the atmosphere. It is true these great floods of wind are so often deflected from the straight course to form local currents, that it appears at first sight as if all were confusion in the atmosphere. But those local currents, though they retard and complicate, do not ultimately prevent the final result by which the "wind returneth again according to his circuits." The "circuits" are the great wind-channels of nature, and in them we see established in the atmosphere a system very analogous to those polarequinoctial streams for ever flowing in the ocean.

The power which sets these currents in motion is nature's mainspring-the sun. An enormous body of air lying over the surface in equatorial regions, being heated and rarefied by the sun, is forced to ascend by the pressure of the adjacent heavier air brought from north and south by the Trade-winds, and this loss is supplied by air from higher and higher latitudes, until at last the poles themselves are reached. But no sooner has a current been established from the poles, than equivalent currents begin to be drawn in from circumpolar regions to supply the void, and this suction, acting backwards through lower and lower latitudes, at length arrives at the original fountain, or suction force, which was the heated air ascending from equatorial regions. Such, in general language, is the circuit of the wind upon the globe.

It has been proved by many interesting observations that currents rising from the earth in warm regions some