compensated for the disadvantages arising from the general uncertainty of the wind, by the continued regularity of its direction through stated seasons: in consequence of which, the merchantman calculates upon the commencement and duration of his voyage with a degree of security and confidence, which sets him comparatively at ease as to the event. These periodical currents of air indeed have been named from this very circumstance the trade winds: and, in illustration of their adaptation to the purposes of commerce, a more striking instance perhaps could not be adduced than the following, which is given in a volume, entitled, "Four Years' Resi"dence in the West Indies," written by a gentleman of the name of Bayley". In the description of the island of St. Vincent it is there stated that a little sloop, the private signal of which was unknown to any of the merchants, sailed into the harbour one morning, and immediately attracted the notice of the surrounding crowd; and the history of its unexpected appearance is thus given. "Every one has "heard of the little fishing smacks employed in "cruising along the coast of Scotland; which carry herrings and other fish to Leith, Edin"burgh, or Glasgow, worked by three or four hardy sailors, and generally commanded by

66

66

r London, 8vo. 1830, p. 292.

"an individual having no other knowledge of "navigation than that which enables him to keep his dead reckoning, and to take the sun "with his quadrant at noonday.

66

66

66

"It appears that a man who owned and com"manded one of these coasting vessels had been in the habit of seeing the West India ships "load and unload in the several ports of Scotland; and, having learned that sugar was a very profitable cargo, he determined, by way "of speculation, on making a trip to St. Vincent, "and returning to the Scottish market with a "few hogsheads of that commodity. The na“tives were perfectly astonished—they had never heard of such a feat before; and they deemed "it quite impossible that a mere fishing smack, worked by only four men, and commanded by "an ignorant master, should plough the bois"terous billows of the Atlantic, and reach the "West Indies in safety; yet so it was. The

66

hardy Scotchman freighted his vessel; made "sail; crossed the bay of Biscay in a gale; got "into the trades; and scudded along before the

66

66

wind, at the rate of seven knots an hour, trust

ing to his dead reckoning all the way. He "spoke no vessel during the whole voyage, and "never once saw land until the morning of the thirty-fifth day; when he descried St. Vincent's right a-head and setting his gaft-topsail, he "ran down, under a light breeze, along the

66

66

"windward coast of the island; and came to "anchor about eleven o'clock under the circum"stances before mentioned."

Such a vessel, and so manned, could hardly have performed the voyage here described, had it not been aided by the current of the trade wind and what then must be the advantage of such a wind, when, instead of aiding the puny enterprise of a single and obscure individual, it forwards the annual fleets of mighty nations. Most important therefore to the Roman empire was the discovery of Hippalus, which enabled its fleets to stretch across at once from the African to the Indian coast by means of the southwesterly monsoons. But, if we would view the subject in all its magnitude, let us contemplate with a philosophic eye the haven of any one of the larger sea-ports of Europe; filled with vessels from every maritime nation of the world, freighted not only with every thing which the natural wants of man demand, or which the state of society has rendered necessary to his comfort, but with all which the most refined luxury has been able to suggest. Merchandise," to use the words of Scripture, "of gold, and silver, and "precious stones, and of pearls, and fine linen, " and purple, and silk, and scarlet, and all thyine "wood, and all manner vessels of ivory, and "all manner vessels of most precious wood, "and of brass, and iron, and marble, and cin

66

66

66

namon, and odours, and ointments, and frankincense, and wine, and oil, and fine flour, and wheat, and beasts, and sheep, and horses, and "chariots."

66

But the importance of all the foregoing points of consideration in the history of the relation of the air to human wants is far inferior to that highest and most beneficial of all its relations, the production of the human voice: for from this source arises articulate language; without which medium of communication between man and man, what would become of the most important transactions of the business of life, as well as of its most rational pleasures, the charms of social converse? But the consideration of the mechanism of the human voice is appropriated to a distinct treatise: and the use of language is adapted rather to the moral than to the physical condition of man: and I therefore forbear to dwell on a theme in itself of the highest interest.

In dismissing the subject of atmospherical air, I would wish to observe how beautiful an instance its history affords of the multiplicity of beneficial effects, of very different characters, produced by one and the same agent; and often at one and the same moment. Thus while we have seen the air of the atmosphere serving as the reservoir of that mass of water from whence clouds of rain, and consequently springs and

rivers are derived, we have also seen that it at the same time prevents, by the effect of its pressure on their surface, the unlimited evaporation and consequent exhaustion of the ocean, and other sources, from whence that mass of water is supplied. And again, while the agitation of the air contributes to the health of man, by supplying those currents which remove or prevent the accumulation of local impurities, it at the same time facilitates that intercourse between different nations in which the welfare of the whole world is ultimately concerned. And lastly, while in passing from the lungs in the act of expiration it essentially forms the voice, it at the same time removes from the system that noxious principle, the retention of which would be incompatible with life.

CHAP. VII.

Adaptation of Minerals to the Physical Condition of Man.

SECT. I.

The general Characters of Minerals.

IT has been shewn in the foregoing chapter, that the constituent parts of the atmosphere are few in number, and of great simplicity in their