When we survey the nations of the earth, we perceive a great diversity among them as to refinement and civilization; and if we further consult the annals of these communities, we find that while some have gradually advanced from rudeness to refinement, as England, France, and Germany, others, which once held an elevated moral position, have descended low in the scale of civilization, as we see in Egypt, many of the nations of Asia Minor, and some of those of Ancient Greece.

The last-mentioned changes show that the condition of political communities is dependent, not wholly on physical causes, which are in the main permanent, but partly also on moral causes, or man's own efforts, which vary greatly in efficiency and degree.

The physical causes of a nation's wealth and prosperity are principally the four following: Fertility of soil, its climate, its mines, and its waters.

I. Fertility

Soils differ very greatly in their power of producing articles useful to man, especially those which are fit for his subsistence - so that while some may annually return to the husbandman from twenty to a hundred times the seed he has sown, others may be utterly barren. Their fertility is mainly owing to the quantity of organic matter which they severally contain, and which once constituted portions of the living animals and vegetables they formerly supported. It also in part depends on the chemical properties of such portions of the earths and stones of which the soil is composed, and which, when reduced into small particles by the action of the elements, enter into the composition of different vegetable products.

This productive power of soils is capable of being greatly increased by human industry, partly by modes of culture, and partly by the addition of animal and vegetable manures, and of certain mineral stimulants of vegetable production, as lime, gypsum, and marl.

II. Climate

The power of a country to support animal life is greatly influenced by its climate. In general, its productiveness is in proportion to the quantity of solar heat it receives, so that the nearer a country is to the Equator, the greater is its vegetable product. Of the cereal, or grain crops, while, in the Temperate Zones, there is only one in the year, there are often two in the Torrid Zone. I was once shown an acre in the Island of Antigua, which had produced eight hogsheads of sugar, equal to 8000 pounds, each pound requiring a gallon of the juice of the cane. There are also many vegetable products, highly prized by mankind, which can be produced only in warm climates. Of this description are sugar, coffee, tea, indigo, and many woods and gums. The orange, the fig, the peach, and the olive, do not thrive in high latitudes.

In the Arctic regions, the vegetable products are comparatively few and of slow growth. Fortunately, most of the cerealia, or grain-bearing plants, grow in the widest range of climates - from the Equator to 60° of North or South Latitude.

The heat of countries, though principally determined by their position on the globe, is also affected by two other circumstances, which it is proper to notice.

The first of these is the elevation of the region above the average level of the earth. In consequence of the perennial heat in the interior of our globe, it is found that the temperature diminishes as we ascend, at about the rate of one degree of Fahrenheit's scale for every 110 yards of ascent, so that regions of great elevation are as cold, and consequently as unfavorable to vegetable production, as lower regions much nearer to the Pole. This effect of elevation is not uniform in the different zones of the earth.

The other anomaly of climate is the difference between the eastern and western coasts of continents - it being found that the eastern are both warmer in summer, and colder in winter, than the western. This fact is the result of a local predominance of the westerly wind, and the difference of temperature on the land and the ocean, both in summer and winter. It is found that, in the Temperate Zones, there is about three times as much wind from the west as the east, in consequence of which, the prevailing west wind on the western coasts of continents has blown over the ocean, and partakes of its equable temperature, both in summer and winter - while the same excess of west wind, on the eastern coasts, has blown over land, and is consequently colder in winter and hotter in summer. Hence, the climates of Western Europe are 10° or 11° warmer in winter than on the Atlantic coast of America in the same latitude, while those on the Pacific coast are similar to those of Europe.