of inland communication;—in these and numberless other ways they offer occasion for all the skill he can display.

A river of any magnitude always forms an important and interesting object of general attention. Both it and the whole extent of area with which it is connected acquire a sort of personal identity, of which it is frequently difficult to find the principle. The name of the great body of water which discharges itself into the sea is generally traced backwards, by popular nomenclature, to one of the sourcesusually the longest. To each branch and tributary there is given a proper name of its own; but this becomes lost when it merges into the main river, losing (like a rich but ignoble alliance) its identity in that of the more illustrious family.

"The origin and progress of rivers, and even the features of their character, bear some resemblance (as has been well observed by Pliny) to the life of man. The river, apparently, springs from the earth; but it has really a higher and nobler origin. Its beginnings are insignificant, and its infancy is frivolous; it plays among the flowers of a meadow; it waters a garden, or turns a little mill. Gathering strength in its youth, it becomes wild and impetuous. Impatient of the restraints which it still meets with in the hollows among the mountains, it is restless and fretful, quick in its turnings, and unsteady in its course. Now it is a roaring cataract, tearing up and overturning whatever opposes its progress, and it shoots headlong down from a rock; then it becomes a sullen and gloomy pool, buried in the bottom of a glen. Recovering breath by repose, it again dashes along till, tired of uproar and mischief, it quits all that it has swept along, and leaves the opening of the valley strewed with the rejected waste. Now, forsaking its retirement, it comes abroad into the world, journeying with more prudence and discretion through cultivated fields, yielding to circumstances, and winding round what would trouble it to overwhelm or remove. It passes through populous cities and the busy haunts of man, tendering its services on every side;-the support and ornament of the country. At last, increased by numerous alliances, and advanced in its course of existence, it becomes grave and stately in its motions, loves peace and quiet, and in majestic silence rolls on its mighty waters till it is laid to rest in the vast abyss.'

To Rivers, then, I beg to devote your attention this even

This eloquent passage is taken from Professor Robison's excellent Treatise on Rivers, which has been made free use of also in other parts of this paper.

ing, and we will, if you please, consider them under three aspects.

I. Their formation and natural features; in short, what we may term their Internal Economy.

II. The great practical uses they serve, and their influence on civilization generally

III. The part they play in the formation and configuration of the earth's surface.

I. What is a river? Whence is its origin? What its end and destination? Some of you, perhaps, have traced the Thames up to its humble fountain-head in the Cotswold; the Rhine to its sources in the glaciers of the Alps; or this, its English counterpart, to the rushy swamps of Dartmoor. But science bids you look farther yet, and find their true pristine source in the sea. A river is, in fact, the representation and embodiment of that wonderful natural phenomenon which prevails over the whole of our planet, and which is so essential to its habitability-I mean the circulation of water to and from the great reservoir of the ocean. Indeed, no epithet could more aptly describe the whole water system of sea and river than that which the ancients applied to the fabled stream Oceanus; viz., πaλíppoos, or "flowing back into itself."

To explain this more fully. You know that three-fourths of the earth's surface is covered by water; and you know also that water, under ordinary atmospheric conditions, has a constant tendency to assume a gaseous form-in other words, to evaporate. If we spill a little water on a tray, we find that it will shortly disappear, and be absorbed into the atmosphere in the shape of aqueous vapour. This effect is, moreover, considerably accelerated by heat, or the motion of the air.

But now suppose a similar effect to be in operation over a water area of 145,000,000 square miles, in many parts exposed to the burning rays of a tropical sun, and swept over and agitated by constant and violent winds, and you will perhaps be able to form some notion of the mass of water which is continually exhaling from the ocean in a gaseous form. I have attempted to make a calculation of this quantity, and I estimate that it may amount to about ten hundred thousand million (or a billion) tons per diem.

To the water thus derived from the ocean may be traced the greater part of the phenomena of meteorology, comprising clouds, dew, rain, &c.; and there is good reason to believe

that many electric and magnetic phenomena have to do with the hygrometrical conditions of the atmosphere, and therefore depend also on the evaporation. But at present we have only to deal with one of these multifarious effects-i.e. Rain.

Much of the water exhaled is redeposited directly in the ocean; but when the air-currents, charged with moisture, pass over the land, they (under certain conditions) cause the aqueous vapour to be massed together in the form of clouds, and ultimately to be precipitated as rain over the surface of the ground.

So far the process has been mechanical; but we must also. notice a chemical element. The water of the ocean is salt, in its natural state supporting only marine life; but in the process of evaporation, only the pure element of water is taken up, free from all saline ingredients; and so by this distillation in nature's vast alembic, a supply of absolutely pure fresh water is generated in the shape of rain. This new condition fits our world for a new and higher order of existence. It is this which affords fertility and beauty to the earth, and furnishes the sustenance necessary for the vegetable and animal life with which it teems.

We have next to consider what becomes of the rain thus distilled. Let us suppose it falling on high land, in the interior of a country. It will generally be disposed of in four ways.

(a) A portion of it will be evaporated back into the atmosphere. If the land be steep and the temperature low, this quantity will be small; but on flatter ground, and with a higher temperature, it may be a large proportion.

(b) A second part of the rainfall will be directly absorbed and utilized by vegetation; this quantity will also vary with circumstances, being but small on rocky ground, where only lichens and mosses can exist, whilst on cultivated soil the absorption will be far larger.

(c) A third portion will sink into the ground; and here again great variation is possible. In the case of hard closegrained rock, or of stiff clay, only a small proportion will enter by fissures or loose places; but into permeable strata, such as gravel and sand, or porous rocks, such as sandstone, oolitic limestone, or chalk, a large quantity will find its way, saturating the strata, and there forming large subterranean reservoirs of water, which will issue at lower levels as springs. To these I will return presently.

(d) After all these deductions there is still a surplus which

will run off the surface of the ground. In the first instance, the trickling drops will find their way into minute indentations in the surface, and will there collect into small rills; these as they flow on will combine to form rivulets; then several rivulets will unite to form brooks or streams; and when these find their way into a common channel they will form a river, which, after receiving farther accessions from other streams similarly formed, called tributaries, will at length discharge into the sea the waters it has collected over the drainage area through which it flows.

And now to return to that portion of the rainfall which, instead of running off the surface of the ground, is absorbed into permeable strata. This water is not permanently buried, but reappears at lower levels, wherever it can escape, in the form of springs, which, of course, go to feed the streams and rivers in their immediate neighbourhood. Many important rivers depend to a large extent on springs of this kind; and in these cases the great subterranean storage prevents sudden and violent floods, and keeps up the quantity in the dry season, the rivers so formed having, so to speak, a larger reserve of water, and consequently being less affected by the fluctuations of the rainfall. Of this the basin of the Thames offers an interesting example. It consists in a great measure of highly porous strata; namely, the well known. chalk formations to the north and the south of London, the great beds of oolitic limestone in the Cotswold region, and sand and gravel in various directions. These absorb a large quantity of the rainfall, and discharge it again in the shape of numerous and often perennial springs. Hence it is that, even in long droughts, it preserves its normal stream. For example, in the summer and antumn of 1868, when scarcely any rain fell from June to September, and the mountain. streams in some parts of the country were almost dry, the Thames was not found to diminish perceptibly below its usual summer flow.

There are also, in many other places, admirable means of regulation in the form of lakes, which are merely depressions in the valleys filled up by the waters of the stream. Everybody appreciates the great beauty added by these lakes to the landscape, but few consider their great utility as equalizers and regulators of the rivers that flow through them. Their large expanse of surface enables them to serve, by varying their levels, as great store-reservoirs for the floods, which, instead of devastating the valleys, are harmlessly laid by, and are given out gradually and beneficially to the lands below.

Rivers have always been favourite subjects for investigation, both geographically and scientifically. The exploration of the rivers of Africa, as we all know, has formed for many ages a most interesting problem, which has not yet been fully solved; and many large rivers in other parts of the world are only imperfectly known. But even in more accessible countries, where the geography and topography of rivers are no longer obscure, we are still often much at a loss for information as to their scientific data. The quantities of water they bring down, the variations of this at different times, the dependence of these variations on local and meteorological conditions, the régime of the flow, the nature of the bed and the banks, and the physical changes they undergo, the quality of the waters and the causes of variation in this particular, the efficacy of the river in its duty as an arterial drain, the action of floods, and where the river is tidal, the nature of the complicated phenomena caused by the combination of the tidal and fresh waters, the formation of bars and shoals, &c. &c.,all these things merit, and indeed require, an amount of exact investigation that they do not often receive, and which I should be glad to stimulate by every means in my power.

II. We have seen that a river is a stream of fresh water, derived in the first instance from the sea by evaporation, and flowing in a definite bed or channel back into the mother

ocean.

"All mountain rivers, lost in the wide home
Of her capacious bosom, ever flow."

We have admired, too, the wonderful mechanism by which nature sustains this process, and the many features of beauty and interest which rivers present to our observation. Our next task is to review some of the more important effects they produce, and the functions they fulfil, by their general influence on civilization, by their supplying the conditions necessary to vegetable and animal life, by constituting to a great extent the means of internal communication, and above all by furnishing our water supply.

With regard to their political influence, I would remark generally, with the late Oxford Professor of History, "that nations, like men, shape their own destiny, let Nature rough hew it as she will." But nature does rough hew the destiny of nations; and the knowledge of her workings and influence is a most essential part of history. This aspect, however, is one so vast, that I should despair alike of your patience and of my own ability to bestow on it anything like an