BOOK III

The subjects comprised in this section of the treatise have reference chiefly to the springs and rivers which appear on the surface of the earth or flow underneath it. The Book begins with a preface, which may have been originally designed to stand at the beginning of the volume. It bears internal evidence of having probably been written at the time of the author’s resolve to take up the discussion of physical problems, as it speaks of old age pressing upon him and leaving him but a short while to cover the immense field which he wished to survey. The years lost among vain pursuits must be repaired by diligence in the task now undertaken; night must be added to day, and every social or business care which can possibly be set aside must be abandoned. The contemplation of the work before him then leads the philosopher into his moralising mood, wherein he inquires what should be the principal object of human life, concluding with the reflection that the best thing a man can set before himself, among the ups and downs of this world, is courage to accept them calmly and to be ready to meet death boldly whenever summoned. To the acquisition of such a courage a contemplation of nature will greatly conduce.

Seneca begins his discussion of the various forms of water by grouping them into two chief classes, standing in collected sheets, as in lakes, or running in channels, as rivers above ground and springs underneath. After a brief enumeration of various qualities of water, he inquires whence the vast volume of water comes that is carried down by rivers to the sea, and how it happens that neither is the earth sensible of this daily loss, nor does the ocean show any perceptible gain. He merely notices the opinion which some philosophers had expressed that the sea does not get larger because it restores to the earth as much water as it receives, allowing its own saline water to sink through endless subterranean winding passages wherein it is purged of its saltness and rises on the land as pure fresh water.[112] Another view, that most of the water supplied by rain eventually finds its way into the rivers, is approximately that at which modern research has arrived, but it meets with our philosopher’s strong opposition. His first objection is derived from his own observation. He tells us that, as a diligent digger among his vines, he can confidently affirm that even the heaviest rain does not penetrate to a depth of more than ten feet from the surface. What is not absorbed by the upper crust of the ground runs at once into river channels, and thence into the sea. He next asks how rain, which immediately flows off the surface of naked rocks, can possibly be the source of the springs and rivers that issue from bare crags, or how springs that appear on the very summit of mountains can be due to rain. Though he could not but be aware of the close connection everywhere observable between evaporation, rainfall, and the volume of springs and rivers, he does not seem to have reflected on its meaning--how in seasons of drought the surface waters fail first, how by degrees the springs begin to lessen and even to cease, how the rivers dwindle until in many cases their beds become almost or quite dry, and yet how, when welcome rains set in, the springs and rivers gradually resume the bulk they had before the dry weather impoverished them. He had made no study of the way in which rain percolates through the soil, subsoil, and rocks underneath, though there are places, such as his vineyard may have been, where, from some impervious material, only a feeble or inappreciable flow of moisture descends beyond a few feet from the surface. Nor was he aware of the innumerable lines of joint by which the most solid rocks are traversed, and which serve as passages for the descent and ascent of water. Had he climbed many mountains, he would have failed to find a spring on the summit of any one of them, unless there had been a sufficient area of higher ground at hand to serve for the supply of the water.

[112] This is the view expressed by Lucretius:

... ut in mare de terris venit umor aquai, in terras itidem manare ex aequore salso; percolatur enim virus, retroque remanat materies umoris et ad caput amnibus omnis confluit, inde super terras redit agmine dulci. --_De Rer. Nat._ vi. 633.

The origin of underground water is regarded by Seneca as due to three causes. The earth itself contains moisture which it forces out at the surface; it includes also air which in the darkness of the subterranean wintry cold is condensed into moisture; by the principle of interchangeability, whereby one element passes into another, the earth in its interior resolves itself into moisture. If it be urged that the rivers are too vast to draw their supplies from these sources, the ready answer comes that the internal reservoir is quite spacious enough for the purpose, and that it might as well be matter of surprise that, with all the winds that constantly blow, the supply of air does not fail, or that a single wave of the sea should be left to follow so many breakers. If the questioner, still unsatisfied, should demand to know how water is produced, he is met with the query how air is produced on earth. There are in nature four elements, and he is not entitled to ask where one of them comes from. Each is a fourth part of nature, and it is obvious that what has an element as its source cannot fail. Hence the philosopher in pronouncing water to be an element has given it enough, and more than enough, of strength. In short, rain may give rise to a torrent, but not a river flowing steadily between its banks. Heavy rains will swell such a river, but cannot produce it.

Having, as he believed, cleared the ground in this way, Seneca proceeds to consider the distribution of water within the earth. He opines that as in our body, so in the earth, there are channels by which both air and liquids flow. He states his conviction that the earth contains not only veins of water, but also large streams, and in a later part of the volume he speaks of both underground rivers, huge lakes, and a hidden sea from which rivers at the surface are supplied (154, 233, 235). He is aware that some of these subterranean reservoirs contain fish, about which he has some incredible tales to tell. He makes mention of rivers that sink underground and reappear, as if a matter for great astonishment. But examples of it may be found in many limestone districts, where the solution of the rock by underground water has given rise to tunnels, passages, and caverns into which, when their roofs give way, surface streams may be engulfed, to break out again from other openings at lower levels (141). The author concludes this part of his argument by asking if anybody is ignorant that there are some standing waters which have no bottom, whence, he contends, it is shown that this water is the perpetual source of large rivers.

The various kinds of taste possessed by natural waters are then discussed, and some marvellous illustrations are given of their effects. Allusion is made to medicinal springs, to petrifying waters, to some with extraordinary dyeing properties, and to others with neither taste nor smell, but rapidly fatal to the drinker by immediately hardening and binding the intestines. Reference is also included to certain kinds of springs, of which the volcanic tracts of Italy supply good examples. Such were those which killed visitors who peered down into the caverns where their waters lurk, and suffocated birds that flew over them. Doubtless many tales were told of the effects of such emanations of carbonic acid gas, like that of the Grotto del Cane which, near Naples, still preserves their classic reputation (134, 261). Again, the same volcanic districts furnished instances of warm, sometimes even boiling, springs, and in alluding to them the author quotes the opinion of Empedocles, who was doubtless familiar with them in Sicily. To complete his record of marvels, the author cites some lakes on which islands float to and fro, of which good illustrations, due to a matted growth of vegetation, were then well known in the Vadimonian Lake (Lago di Bassano),[113] and he mentions other lakes in which he had equal faith, with water so heavy that brickbats would float upon it, and nothing, however heavy, not even hard solid stones, would go to the bottom.

[113] Pliny, _Hist. Nat._ ii. 96. Pliny the Younger, _Epist._ viii. 20.

Seneca is inclined to agree with some philosophers that certain rivers of peculiar and inexplicable character were created along with the world, and he specially cites the Danube and Nile as examples, these vast streams being too remarkable to have had the same origin as other rivers. Accordingly he reserves the Nile for consideration in a later part of his volume (166). There is another kind of water which, with his Stoic brethren, he places at the beginning of the world--the great ocean and every sea that flows from it between the lands. Yet he found no place in any part of the treatise for a discussion of the phenomena of the ocean.

The Book closes with a vivid description of the probable catastrophe by which the end of the world will be brought about. That the present condition of things will be swept away to make room for another and better race of men he assumes as a matter of certainty, and he tries to picture by what physical means the destruction will probably be effected. He is certain that it will be by no one agency, but that all the energies of the world will be called forth to compass the destruction of the human race, nothing being difficult to nature, especially when she is hurrying towards her end. The picture which is given of the progress of the great deluge forms by far the most striking piece of writing in the volume. It ends somewhat inartistically in some gibing criticism of a quotation from Ovid. But the poetic afflatus had not been quite quenched. The author immediately returns to the subject in the succeeding and final chapters, and after enumerating the different agencies that may be called out to effect the destruction of the world, he draws a lurid scene when a single day will see the burial of the whole human race.[114] After this act of divine wrath has been accomplished, the waters will disappear below ground, the sea will retire to its own abode, and on the renovated earth every animal will be created afresh, and a new race of men will be installed, ignorant of sin and born under better auspices.

[114] So Lucretius:

... maria ac terras caelumque-- una dies dabit exitio. --_De Rer. Nat._ v. 92, 94.