By Sir Archibald Geikie, K.C.B., Pres.R.S.
The treatise of which the present volume is a translation possesses a twofold interest. In the first place, it is probably the last literary work of a man who filled a large space in the Roman world of his day. After a varied career as philosopher, barrister, politician, statesman, courtier, and man of letters, he at last incurred the implacable enmity of Nero, to whom he had been tutor. Having in his youth paid some attention to physical inquiries, he had then been led to prepare and publish a book on earthquakes. But in subsequent years the absorbing cares of State probably left him little leisure to continue these studies, for which, however, he had retained his taste. Hence, when in his last days he sought in retirement to devote himself to philosophical pursuits, he naturally turned to some of the physical problems that had interested him in earlier life. The earthquake which on 5th February A.D. had done much damage to the towns of Campania, revived his youthful enthusiasm for the investigation of such phenomena, and may possibly have suggested to him the preparation of another volume dealing with this and other scientific matter. We know at least from the book itself that he wrote a part, if not the whole, of it after that date (221, 230),* and that he took pains to collect information about the catastrophe. As he was in the habit of sojourning on the shores of the Bay of Naples, he probably visited the scene of destruction himself for the purpose of his book. We learn from Tacitus that it was immediately after his return from Campania to his villa near Rome, bringing with him, we may suppose, his nearly completed manuscript, that Seneca received the Emperor’s order to commit suicide.
* The numbers within parentheses throughout these Notes refer to the pages of the Translation.
In the second place, Seneca’s work on Natural Questions stands out as one of the few treatises on physical science which have come down to us from antiquity. It is interesting alike for the quotations it contains from the works of previous authors, some of which have not survived, and for the criticisms and opinions which he himself expresses on the various subjects of which he treats. It can hardly, however, be regarded as an original contribution to science. Its author’s life had been spent in other and widely different pursuits, which led him far away from scientific inquiry. But as a summary of the general state of knowledge in his day, made by a man of strong intellect, who had been trained in the legal and philosophical schools of the time, and had read widely and reflected much on these matters, the book may be taken to afford a fair presentation of the manner in which a number of questions in astronomy, meteorology, and physical geography were regarded by thoughtful minds in the first century of our era.
In judging of the intrinsic merit of such a work as the present, the modern reader finds a difficulty in realising from the broad platform of natural knowledge which, after the labours of the intervening centuries, has now been laid, how exceedingly narrow was the circle of ascertained fact available to the student two thousand years ago. The spirit of scientific observation and experiment had not then been developed, yet the familiar phenomena of everyday life pressed, as they still do, for explanation. Man’s knowledge of nature was then too limited to furnish a basis for distinguishing what was fact from what was mere guesswork. In the infancy of our race, as in the childhood of the individual, the tendency of the human mind is to perceive resemblances rather than differences. Analogies are readily observed and, in default of knowledge of the facts involved, are mistaken for identical sequences of cause and effect. Throughout the interpretations of natural phenomena given by the philosophers of antiquity, it is remarkable to what a large extent the meaning of one appearance is explained by comparing it with another to which in reality it may bear no resemblance. Seneca’s volume abounds in examples of this use of analogy.
The authority of great names exercised a wonderful fascination on the minds of the early investigators of nature. Generation after generation of writers were led to accept with little or no modification the dicta of eminent philosophers who had preceded them. An observer might sometimes recognise the erroneousness of the opinion of a predecessor, and yet lack the means of detecting the falsity of his own, which nevertheless he propounded with full assurance of its truth. In such circumstances criticism had no secure foundation, while credulity, rampant in the world outside, could hardly fail to show itself in philosophic circles. Even the most cautious and truth-seeking inquirer might easily and almost inevitably be led to accept statements which did not seem to him unreasonable, and which no previous experience of his own or others warranted him to disbelieve or even to suspect.
It behoves us, therefore, to be on our guard lest, from our much higher standard of knowledge, we may be tempted to look with amused contempt on the puerile conceptions of nature to be met with in the writings of the ancients—the grave assertion of absurdities as actual facts, the inept analogies, the confident explanations which are no explanations at all, and the complete absence of any attempt to test by examination or experiment the validity of statements which with but little trouble could have been disproved.
These evidences of the exceedingly imperfect knowledge of his time are fully illustrated in Seneca’s chapters. He quotes some two dozen of previous writers who had dealt with the same or cognate subjects. It is needless to say that they were Greeks, no place having yet been found in Latin literature for treatises on Science. The author most frequently cited by him is Aristotle, whose Meteorologica he had evidently studied with care. He gives frequent quotations from that work, but even where he does not specifically quote, his views generally accord with those of the great philosopher and naturalist.102 Almost the only quotations from the works of his own countrymen are verses from some of the poets, especially from Virgil and Ovid. It is remarkable that he makes only one quotation from Lucretius, although he would have found in that poet’s noble work many passages more apposite to his subject than those which he has taken from the Aeneid, the Georgics, and the Metamorphoses. We may suppose that these works were favourites with him, and that he knew much of them by heart, but that he was less familiar with the De Rerum Natura.
It is manifest from the present volume that its author, like Lucretius before him, had a lofty conception of the dignity and moral influence of the study of nature. This pursuit seemed to him to raise us above the sordid things of life and to withdraw the mind from the body—a dissociation so eminently beneficial to our higher aspirations. He believed that in the study of the hidden phenomena of the universe a mental alacrity is developed which will be found to be not without practical utility in the conduct of affairs that lie nearer the surface (113).
With this clear recognition of the importance of his theme he resolved in his old age to enter upon a task which other less worthy pursuits had hindered him from pursuing. He would now attempt to survey the universe, unravel its secrets, and give the results of his studies to the world (109). It was not, however, his aim to compose a systematic treatise on Natural Philosophy, but rather to take up some special subjects and deal with them in the light of what had already been written upon them, and of what his own reflections suggested. His undertaking assumed the form of a series of epistolary essays addressed to his friend Lucilius Junior, procurator of Sicily. The literary shape thus selected allowed the use of an unconstrained, almost colloquial, style which would not have been suitable to a more ambitious work.
Had Seneca designed to prepare a formal or methodical treatise, he would doubtless have planned it to include the three sections which he regarded as comprising every inquiry that can arise as to the nature and constitution of the Universe (Universum)—celestial, atmospheric, and terrestrial (Caelestia, Sublimia, Terrena, 51). The world (Mundus) in his view comprehends all things that come or can come within our cognisance (54). Instead of entering upon a full discussion of any one of his three sections, he selected from them a few topics which had probably more particularly engaged his attention. Most of these belong to the second or atmospheric division of his scheme of arrangement, to which he devotes six of his seven books, the remaining one being given to the discussion of some celestial phenomena. Certain subjects which we should naturally range in the terrestrial series, such as the source and flow of rivers and the nature and origin of earthquakes, he explicitly includes among his atmospheric phenomena (51).
It appears to be probable that Seneca had neither finished nor revised his manuscript at the time of his death. Parts of the work are obviously incomplete, though some of these gaps may be due to defects of transcription or to the subsequent loss of parts of the text. The obscurities of language, which are not infrequent, may likewise have partly arisen from lack of the author’s revision of his original copy. His discussion of the problem of the rise of the Nile suddenly breaks off in such an abrupt manner as to suggest the loss of a portion of the original volume. One of the most important omissions is the absence of any account of the phenomena of volcanoes. The author does indeed refer in several places to this subject, but with Aetna before him, of which so many Greek and Latin poets had sung, and which had so often been referred to in the writings of the philosophers, he could hardly have meant to offer no commentary on so notable a feature in the geography and history of his own country. We know indeed that he was keenly interested in this mountain, and that he wrote to Lucilius to ascend the volcano and send him particulars about it. In the letter conveying this request he alludes to some of the Roman poets who had sung of its wonders, and urges that a description of Aetna should form part of a poem on which his correspondent appears to have been then engaged.103 Another important subject in physical geography finds no place in Seneca’s volume—the Sea. Of the outer ocean it was not to be expected that he could have had much to say, but we can hardly suppose that he would have considered his essay complete without some discussion of the various phenomena presented by the Mediterranean Sea.
A century before Seneca’s prime, the immortal De Rerum Natura of Lucretius had appeared at Rome, wherein the origin and constitution of the world were sung with the intense earnestness, brilliant imagination, and resounding cadence of a great poet and with the grasp and penetration of a great philosopher. In this splendid work some of the problems discussed by Seneca were considered, and explanations were given of them with the usual undoubting confidence of olden time. In literary quality the two writers stand far apart, yet it is not uninteresting to compare their respective views of nature. The vivid and often majestic diction of the one is not more diverse from the somewhat familiar and conversational tone of the other than are their respective creeds. Lucretius was a convinced and enthusiastic Epicurean, and in accordance with the teachings of his master denied the existence of any divine co-operation in the plan and government of the Universe,
nequaquam nobis divinitus esse paratam
naturam rerum,104
although no writer either of ancient or modern time has had a more overpowering sense of the beauty, majesty, and order of this world. It was his earnest purpose to show men how, by a contemplation of the face and ordered scheme of nature, they could free themselves from the bond of religious superstition and the fear of death.105
Seneca, on the other hand, held the Stoic belief in an all-wise and omnipotent Creator. In an eloquent exordium to his volume, and in a peroration near its end, he affirms his conviction that this Divine Being is all in all, at once within and without his works; He has clothed himself with creation, but is hidden from our eyes and can be perceived only by thought (3, 7, 305). Our philosopher could not conceive of anything more beautiful, more orderly, and more consistent everywhere in plan than the world around us. That such a world should have resulted from the tumult of chaos, by the mere chance collocation of atoms, appeared to him the madness of vulgar error. Yet it was only too true, though it might be thought hardly credible, that even philosophers had been tainted with this pernicious doctrine. Hence it would be in the author’s judgment a profitable task to inquire into the truth concerning these matters. To explore this world, he remarks, is far more than enough for a single lifetime. Whether what we may be led to believe regarding it shall be true must be decided by those who may attain the knowledge of the truth; we can but examine and conjecture, with no certain assurance of discovery, yet not without hope (304). It behoves us to be ever watchful against forming conclusions rashly, disrespectfully, or ignorantly, and of being knowingly untrue. In this quest after knowledge, while much may be found out which will be of practical usefulness, we are encouraged to advance, not by any hope of gain, but by the wonder with which the inquiry fills the soul. To obtain a knowledge of Nature is the highest reward to which the mind of man can aspire (230, 304). Seneca’s practical conclusion was thus much the same as that of Lucretius. He does not, however, attempt in this volume to enforce it with the solemn earnestness shown by the poet, though he loses no opportunity of inveighing against the follies and vices of his time. In discussing natural phenomena his first desire is to explain them, and in so doing to animadvert on the explanations of previous writers, with perhaps a not unnatural wish to show his own ability as a critic and expositor.
It was in due accordance with the principles of his school, as well as with his own natural temperament, that Seneca should continually be led to draw ethical lessons from the physical phenomena which he discussed. The interpolation of some of these reflections may occasionally seem to a modern reader rather irrelevant and far-fetched, but there can be no question as to the spirit of reverence with which he approached his subject. Like other philosophers who had preceded him, he maintained this spirit, while at the same time he had discarded the crowded and confused polytheism of the prevalent mythology. But he here keeps this antagonism in due restraint, only occasionally expressing his dissent from the popular creed. He would not admit that even the old philosophers could have been so foolish as to credit the gods with some of the acts which had been popularly attributed to them. He refused to believe that the guardian and ruler of the Universe hurled thunderbolts with his own hand. Still less could he suppose that the gods had lighter bolts with which they amused themselves in play. His expression (fulminibus lusoriis, 91) recalls the bitter irony of Lucretius and the sarcasm of his question whether, when the gods aim at lonely places or at the sea, they are only at practice to strengthen their arms.106 But Seneca held with Lucretius that in the contemplation of nature we obtain the courage and elevation of mind which fit us for the trials of life and the coming of death (113).
In the treatment of scientific problems Seneca displays the same unhesitating assurance of the truth of his opinions, which was characteristic of the philosophers of antiquity. These writers had hardly a glimmering conception of nature’s infinite complexity, of the extreme diversity and intricacy of natural processes, of the unbroken and endlessly ramifying relations of cause and effect, of the long and patient investigation by which alone these relations could be unravelled, and of the caution and diffidence with which conclusions regarding them should at least for a time be formulated. Seneca frequently passes caustic criticisms on the views expressed by his predecessors. He styles the philosophers, as a body, “a credulous folk.” Some of them he even goes so far as to accuse of perpetrating deliberate falsehoods (276, 286, 289). Nor does he hesitate to banter his brethren of the Stoic School, whose “absurdities,” as he calls them, he cannot refrain from quoting.
Yet when his own opinions are examined in the light of the present day, they are found to be in many cases no nearer the truth than those which he rejected with contempt. It is, indeed, sometimes difficult to realise the mental position of a man who could adopt and propound them. In many cases he accounts for a phenomenon by the analogy of another to which it has no real affinity, as where he explains halos by the circular undulations produced on a surface of water into which a stone is thrown (13). He sometimes suggests an experiment to prove the truth of his assertion, but if he had made the experiment he would have found how completely it failed to support him, as, for instance, when he states that a large pond of water reflects only one image of the sun, but that, if it is divided into several smaller ponds by the insertion of partitions, it will show as many images as there are divisions (18). Striking also and numerous are the examples of his credulous acceptance of statements which, had it occurred to him to test them by actual examination, he could easily have found to be erroneous. He affirms, for instance, more than once, that while lightning melts metals, it freezes wine, and he gravely alleges that when the wine is thawed and imbibed, it either kills or drives mad those who partake of it (79, 97). He asserts that the waters of certain rivers have the power of dyeing whole flocks of sheep, black fleeces being changed into white, and white into black (137), that some waters are so dense that even the heaviest objects will not sink in them (138); that the heat of the sun in the Nile valley is so great as to melt silver and the joints of statues (173). When he proceeds to explain the reason of such abnormalities he expresses no hesitation, but delivers his opinion with the assurance of a professor who has obtained the experimental demonstration in his laboratory.
It is remarkable that although some progress had been made in astronomy, especially by Greek philosophers, before the beginning of the Christian era, the conclusions arrived at by these observers regarding the relations of the earth to the other heavenly bodies met with but little acceptance for many centuries, even among reflecting minds. Lucretius, for example, still believed the earth to be the centre of the Universe to which all the heavier materials had converged, while the fire-laden ether escaped to the outer boundaries of space, sun, moon, and stars occupying an intermediate place. He did not think that the sun can be much larger than it looks to be to our senses, nor was he quite sure whether it is the same sun which, passing under the earth, reappears in the morning, or if at the close of each day the sun is extinguished and a new collection of fires makes a fresh sun in the morning. He was quite aware of the different views of Chaldaean sages and astronomers, but in such questions he could see no reason why one theory should be better than another.107
Seneca, however, had, on the whole, a more advanced appreciation of the relations of the earth to the heavenly bodies. He believed the sun to be larger than our globe, and that a thousand stars might be put together without equalling his mass (284, 288). He thought the heavens to be so vast as to afford space for the swiftest of the planets to rush along with uninterrupted speed during full thirty years (7). He showed his enlightened outlook upon astronomical possibilities when he surmised that comets may have orbits that carry them far beyond the Zodiac, and when he conjectured that other planets than those then known remained to be discovered (296–299). And yet, sharing these more enlarged conceptions, he clung with curious pertinacity to some of the old childish faith which was natural in the infancy of mankind. He knew that some philosophers held that it is the earth which revolves and not the heavens, and though he does not deliberately reject this opinion, it is evident that he still held that the heavens circle round the earth.108 Again and again he expresses his conviction that the force which sustains the energy of the sun and the stars consists of the exhalations that arise from the surface of the earth. These exhalations, he says, are the pasturage of the heavenly bodies, the breath of the world. It would be impossible, he asserts, for the earth to furnish so ample a store of nourishment to bodies larger than itself unless it were full of breath which is passing off from every part of its surface both by day and night. To the obvious objection that the supply of this energy would soon become exhausted, he has the reply that this exhaustion would certainly take place were it not that the elements are in a condition of continual transformation, issuing in one form, passing into each other, and returning to their original positions, thence to begin their cycle anew (55, 198, 244–5). In this universal transmutation water passes into air, air into water; air likewise is changed into fire, fire into air, while earth is formed from water, and water from earth (120).
In his general conception of the universe, Seneca, as a Stoic philosopher, recognised a principle of evolution. He believed that the world embraces in its constitution everything that it is destined to experience from its beginning to its end. As a human embryo contains the germ of the future man, so at the first creation of the universe, sun and moon, the changes of the stars, and the birth of living things were all embraced. And there were likewise included the forces whereby the earth is affected, and which will ultimately lead to the final destruction of the globe (151).109
With regard to the earth itself, whether it is to be regarded as a soul or as an organised body, Seneca announced his conviction that it has been constructed much after the plan of our human bodies. As in these bodies, veins and arteries are provided for the reception of blood and breath, so in the earth there are passages, some for the transport of water, others for the flow of air (126). He was sure, also, that everything on the surface of the earth has its counterpart beneath—caves, mountains, lakes, and rivers.
In this part of his Essay the author has grouped together a variety of phenomena, some of which are meteorological (in the modern sense of that word), and belong therefore to his class of Sublimia, while others are astronomical, and would be properly placed among his Caelestia. They all have reference to light in some form, and doubtless for that reason were considered as a series. Seneca, largely swayed by the opinions expressed in Aristotle’s Meteorologica, agrees with that philosopher in the belief that the earth gives forth various kinds of exhalations, among which some contain the seeds of fire. He thought that high up in the air, among dry and hot elements, these fires may be kindled by the sun’s rays, and further, that when the atmosphere becomes violently disturbed its friction may give rise to fires (9, 10, 39).
With these ideas, which he held as established truths, it is easy to understand that he should have regarded as extremely foolish the notion that any of the lights which move rapidly across the sky are of celestial origin. Had such been their source, he felt sure that by this time there would have been none left in the firmament; yet although no night passes when some of them may not be seen, each star in the sky is found to maintain its place and its size. Hence he confidently concluded that the meteors, which are seen at night, and sometimes even by day, have their birth far below the stars, and are soon extinguished in their course because they have no solid and abiding resting-place. Single aerolites and even showers of stones had been recorded in Roman literature as having fallen from heaven, but it had not yet occurred to any observer to connect them with the shooting stars which gleam across the nocturnal sky, and are now recognised to be due to meteorites of different sizes, entering our atmosphere with planetary velocity, there breaking up with varying luminosity, and remaining visible for shorter or longer intervals of time.
The author appears to have regarded as akin to these meteors the star-like balls of light, which in stormy weather are sometimes seen on the masts of vessels at sea, and which before his time had been observed on the points of the spears of an army in the field. This luminous appearance, regarded by the Romans as a sign of the friendly presence of Castor and Pollux, is entirely atmospheric, and has no connection with shooting stars. It is now known as St. Elmo’s Fire, and has been shown to be a gentle continuous electric discharge from the earth towards a cloud.
Seneca next describes in some detail a series of optical appearances connected with the sun and moon. Until the laws of the reflection and refraction of light had been discovered, it was obviously impossible to account for these phenomena. There is, therefore, much interest in following the lines of thought by which the old philosophers attempted to explain them. Seneca clearly perceived that the halos and coronae seen round the sun and moon in certain states of the atmosphere do not belong to these luminaries, but to our own air, and may furnish indications of coming weather. He remarks shrewdly enough that appearances akin to those seen in the sky may sometimes be observed in the thick moist air of a bathroom. But when he confidently proceeds to explain the meteorological phenomena he betakes himself to analogy, as he is so fond of doing. He remarks that when a stone is thrown into a pond a succession of circles is produced on the surface of the water, which continually widen from the point of impact until they lessen and disappear. In like manner he believes that when the light of the sun or moon strikes the cloudy air it produces a similar effect, for as every kind of light is round in shape, the air is thus driven into a circular form. His love of analogy generally, as in this instance, leads him far away from the truth, and prevents him from seeing the palpable flaws in his reasoning. But the apparent similarity of appearances, which are in reality entirely dissimilar, contents him with his explanations.
His discussion of the rainbow (16–33) is one of the most detailed and vivacious in the whole volume. It takes the form of a sustained argument, in which the author cites various authorities, and replies to objections brought by a supposed opponent to his thesis, which is that the rainbow is unquestionably an image of the sun received in a very moist cloud which has the shape of a round concave mirror (20, 27). He quotes with apparent approbation the opinion that in a shower of rain each falling drop is a mirror reflecting an image of the sun, and that when an observer stands directly between the sun and the shower he sees the reflections of the countless drops blended into one continuous semicircle. But as the discussion proceeds the writer denies that the cloud consists of separate rain-drops, and he maintains that even if it did they would not unite to give one unbroken image. In proof of his contention he urges the fallacious assertion that if a number of mirrors are joined together and a man is placed before them, each gives its own reflection, and thus a single man becomes multiplied into a crowd. If he had ever tried the experiment or had visited the shop of a mender of mirrors, he would have seen that the separate pieces, if strictly arranged on the same plane, reflect a single image. His imaginary antagonist asks for an explanation of the rainbow-like colours displayed by the spray from a burst water-pipe, or the splash from an oar, which are, of course, cases strictly parallel to the falling shower of rain (24). The resemblance is at once granted, but is explained away on the ground that the drops fall so quickly that they cannot form reflections of the sun, and that to produce such reflections the medium must be at rest. The objector once more strikes in with a reference to the rainbow colours to be seen in a glass rod which is placed obliquely in the path of the sun’s rays (30). These prismatic tints, as has long been known, are due to the same decomposition of white light, as in the rainbow. But Seneca claims the illustration as furnishing additional arguments in his favour. He maintains that no colour is really produced in the rod, but only a false appearance of colour, his idea being apparently that unless the colour is inherent in an object apart from direct sunlight, it is only apparent and not real. The glass, he says, tries to reproduce the sun’s image, but fails because of its unsymmetrical form, the reflections being crowded together and confused into the appearance of a single band of colour. In regard to the falling drops of rain in a shower he contends that they receive the colour but not the image of the sun, and he is led away by the false analogy of the varying tints of a peacock’s neck as the bird tosses its head (25). At one part of the discussion he affirms that the colours of the rainbow come partly from the sun and partly from the moist cloud (21). Further on, however, he agrees that they proceed from the sun, but are only apparent, for if another cloud comes across the face of the luminary they at once vanish (29). The greater diameter of the rainbow compared with that of the sun as seen by us he accounts for by the analogy of a concave mirror, which greatly enlarges the objects reflected from it. At the conclusion of the discussion he repeats his belief that the rainbow and the corona or halo have no definite material inherent in them, but are like a mirror which reveals only a deception, the mere phantoms and empty imitations of real bodies, which certainly do not exist in the mirror, and therefore cannot come out of it (41).
In Chapters XVI. and XVII. the author indulges in one of his favourite moralising episodes, suggested by the topics he has been discussing in the previous pages. He takes the existence of reflecting surfaces as his text, and from the calm surface of still water passes on to artificial mirrors, contrasting the manners and morals of early mankind, who had only pools and lakes in which to see their faces, with the luxury and vice of later ages, when the use of metals led to the invention of metallic mirrors. In this retrospect, however, he places the discovery of the use of iron before that of the other metals. The priority of bronze and the reason for it are accurately stated by Lucretius:
et prior aeris erat quam ferri cognitus usus,
quo facilis magis est natura et copia maior.110
In this division of his work the author discusses various aspects of the atmosphere and offers an explanation of the phenomena which he describes. He distinguishes between the very bright ether on high, and the moist, denser atmosphere which underlies it, but thinks that they must pass insensibly into each other (66). The atmosphere he regards as a continuous non-composite body, capable of great range in tension, and forming the vehicle through which the exhalations from the earth pass outwards to the sky. It does not everywhere possess the same qualities. In its lower parts next the earth it is dense and misty, owing to the terrestrial exhalations, and is there warmed by the earth’s breath, by the reflection of the sun’s rays from the ground, and from the fires, artificial and subterranean, as well as from the warmth communicated by living animals and plants, for life cannot exist without heat. The highest portions of the atmosphere are exceedingly dry, hot, and attenuated, owing to their nearness to the eternal fires and the heat of the heavenly bodies. The middle parts, on the contrary, are intermediate in character, but colder than what lies above and below them (60, 61). It is the lower portions that are subject to the greatest changes, for they receive the earthly elements which involve such constant turmoil. The instability of the air arises also in part from the motions of the earth and from those of the sun, moon, and stars, to which cold, rain, and other atmospheric disturbances are due (56, 61).
Seneca, in passing on to discuss the nature and origin of thunder and lightning, divides the phenomena into three kinds—lightning-flashes, thunderbolts, and thunderings (62). After citing and commenting on the opinions of various philosophers he proceeds to give his own views regarding these appearances. The lightning flash (fulguratio) he looks upon as fire widely spread out, the thunderbolt (fulmen) as fire condensed and hurled with violence (66). The difference between the two is in force rather than character; a flash is a bolt without strength enough to reach the earth, while a thunderbolt is lightning in its most intense form (69). With regard to the origin of the fire he points out that fire may be artificially produced in two ways: either by percussion, as when stones are struck; or by friction, as when two bits of wood are rubbed against each other. He thinks that probably in both of these ways clouds may emit fire, and that in the violence of storms a source of energy is supplied whereby the warm or smoky exhalations from the earth may be kindled and fall with a fierce glow to the earth (70, 101). These exhalations contain dry and moist bodies, to which heavier elements may be added. A combination of such materials will form a thicker and more solid cloud than one of pure air, and such a cloud may burst with a loud report (78). There can be no peal of thunder unless the hollow clouds are broken up with great violence (76). The characteristic path of the thunderbolt is determined by the oblique current of air in which, while the natural tendency of the fire is upward, the violence of its discharge presses it downwards and compels it to take up a zig-zag course. The peculiar ozone odour noticed during thunderstorms, and long popularly known as the smell of sulphur, is alluded to by Seneca (69, 97) and by Lucretius.111
The discussion of these subjects leads on to a disquisition on the portents that may be drawn from different kinds of thunder and various forms of lightning. Seneca infers from the effects produced by it that lightning possesses an inherent divine power. Among these effects he enumerates some in which he seems to have thoroughly believed, such, for instance, as the smashing of a wine jar already quoted, and the freezing of the wine for the space of three days thereafter. He is thus disposed to attach credit to the opinion that future events are foretold by both lightning and thunder. Yet he cannot change his Stoic faith that fate, that is, the necessity for the happening of all things and all actions, can be set aside by no force, can be altered by no portents, nor averted by any prayer or sacrifice. Though he admits that vows and supplications may be useful to the worshippers, he knows that even these also are included in the decrees of fate.
These reflections lead the philosopher to a characteristic peroration on the moral lessons to be derived from the subjects he has been discussing. From the dangers incident to thunderstorms he passes to the enforcement of the Stoic doctrine that death must be despised, and everything which leads to death will then cease to have any terror.
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.
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.
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.
This section of the treatise begins with a denunciation of flattery and ends with another against luxury. Neither the preface nor the concluding chapter have any obvious connection with the text between them. It is curious to note that while Seneca here warns his friend Lucilius against flatterers, and inculcates how their approaches are to be met, he himself in this very volume perpetrates four pieces of flattery to the despicable but all-powerful Nero. He quotes a prosaic line from a poem of the emperor’s, which he characterises as “most elegant” (disertissime, 25). He refers to Nero as most devoted to truth as well as to the other virtues (235); he refers to the advent of a comet which appearing in Nero’s reign had redeemed these heavenly bodies from their evil repute (290), and he describes that reign as “most joyous” (laetissimus, 294). The old courtier, so long habituated to the language of flattery, was perhaps hardly conscious that he was here making use of it, or he may naturally have reflected that at a time when the emperor had ceased to bear him any good will, the absence of the customary adulation might cause as much offence as if a direct insult were intended.
When from his ethical lecture he turns to resume his physical disquisitions, it is the mysterious Nile to which he devotes attention. After a brief contradiction of the statement of some philosophers that the Nile and the Danube are similar in their characters, he enumerates some of the well-known peculiarities of the river of Egypt. A problem which greatly exercised the minds of the philosophers of antiquity, and which has only been finally solved in our own day, was the cause of the annual rise of the Nile on which the fertility of Egypt depended. Seneca says with justice that if the point of the river could be ascertained where the rise begins the question would be settled. He does not appear to have known much about the river, for he believed that the water is for the first time collected into a single channel at Philae. In his account of that place and of the cataract there (168, 169), he speaks of the river’s egress from Ethiopia, and of deserts which are crossed by the trade route to the Red Sea. In a subsequent part of the treatise he gives the interesting and important information that he had himself seen and conversed with two centurions who had been despatched by Nero to discover the source of the Nile (235). From them he learnt that they had penetrated far into the heart of Africa, and had reached a region of illimitable marshes where the river was so covered and impeded with vegetation that neither on foot nor by boat could it be ascended. There can be no doubt that these enterprising explorers had come to the sudd, which in recent years has been found so serious an impediment to navigation. They informed Seneca that in the marsh region they had seen with their own eyes “two rocks from which an enormous body of the river came out.” There are apparently no rocks along the course of the Nile in the present marsh region, which is a vast flat, and it is therefore difficult to conjecture to what the two military surveyors allude. Possibly they saw the mouth of some affluent of the main stream such as the Khor Adar, or the sudd may have extended further north than it does now.
Seneca’s account of the Nile derived from travellers and previous writers gives a clear summary of what was then known about the river, but of more interest is his discussion of the opinions that had been propounded before his time as to the cause of the annual rise. He first quotes the view of Anaxagoras, shared by the Greek tragedians and widely accepted, that this rise was due to the melting of snow on the uplands of Ethiopia. This idea he cogently combats by adducing various kinds of evidence of the great warmth of the climate in those southern regions. Some of these proofs, indeed, are exaggerations, as where he affirms that silver is unsoldered or melted. But one of his proofs, drawn from the habits of the animals of the country, is worthy of notice. He remarks that no hibernating creature is found there, and that even in midwinter the serpent is seen above ground. He argues that in Africa, as in Europe, melting snow would swell the rivers in spring and early summer, whereas the Nile flood continues to rise later during four months.
In a subsequent part of this treatise (235) allusion is made to an explanation which had been given of the rise of the Nile, that it is due not to the fall of rain from above but to the outflow of water from within the earth, and it is in connection with this opinion that he cites the experience of Nero’s two centurions above referred to, as if he were disposed to believe that what these explorers saw was really a vast body of water issuing from underground.
The opinion of Thales is next criticised that the Etesian or northerly winds drive the waters of the Mediterranean against the mouths of the Nile and consequently pond back the waters of the river. This view was of course entirely erroneous, but though Seneca rejects it, he does not seem to have quite understood it, for he argues that, coming from the same quarter as the winds, the Nile water should not have been turbid, but clear and blue, like that of the sea. In commenting upon the futile support given by Euthymenes of Marseilles to the idea of Thales, Seneca throws light on the wide extent to which the coasts of the outer sea had then been made known by trading vessels.
In rejecting another explanation proposed by Oenopides of Chios, the author shows that he is aware of the fact that caves and wells are warm in winter and cool in summer, and that he has partly divined the reason, when he states that in winter they are warm since they do not admit the frosty air from without and in summer they feel cold because the warm air from outside has not penetrated into their recesses. He returns to this subject in Book VI. (241).115
After mentioning and dismissing a grotesque suggestion of Diogenes of Apollonia, Seneca suddenly drops the discussion of the Nile and passes on to the subject of hail. It is obvious that there is here a serious gap in the text. It is not probable that he meant to leave off his examination into the probable sources of the Nile without stating his own view of a matter which had been so long the subject of wonder and debate. Either, therefore, he never completed this section of his treatise, or a portion of the work has been lost.
The remainder of Book IV. is taken up with a desultory discussion of the subjects of hail and snow, written when the author must have been in a somewhat frivolous mood. He begins by telling Lucilius that if he were to assert that hail is produced as ice is with us, a whole cloud being frozen, he would be rather audacious. So he will imitate the chroniclers, who after they have told a great many lies, refuse to be responsible for some one statement, and refer for its truth to the authorities. If, therefore, his friend doubts his word, he will call in Posidonius, who will tell him that hail is formed from a watery cloud just turned into liquid. No teacher is needed to explain why pellets of hail are round, for all drops take that shape. Hail is nothing else than suspended ice, and snow is suspended hoar-frost. In this light vein Seneca thinks he has finished the subject and might dismiss it, but he cannot resist the temptation to continue the persiflage a little further. He quotes in a bantering style some of the opinions of his brother Stoics, and after this long preamble begins an inquiry into the distribution of density and temperature in the atmosphere.
It would have been interesting had he seriously and fully stated what was known or surmised on this last topic, but he dismisses it in three short chapters. We learn from these that he regarded the air to be densest next the earth, and that as all things retain heat better the denser and more compact they are, so the air becomes less warm in proportion to its height (184).116 The opinion of some persons, that the air on mountain summits ought to be warmer because they are nearer the sun, is sagaciously controverted, and the insignificance of all inequalities on the surface of the earth in comparison with the distance from the earth to the sun is forcibly expressed and illustrated.
The subject of snow and hail is briefly reintroduced at the end of the Book, probably for the purpose of affording a convenient introduction to the invective against luxury which fills the concluding chapter. The preservation of snow in ice-houses, and its use in the reparation of jaded appetites by cooling drinks, calls forth a denunciation of the young rakes of his day, which closes the discussion.
The movements of the atmosphere form the subject of discussion in this part of the treatise. In the first chapter the author seeks for an exact definition of the term “Wind” (ventus), and ends by adopting one which is obviously inaccurate—“wind is air flowing in one direction,”—for as he afterwards speaks of whirlwinds he was well aware that the movement may be in every direction, or vorticose. Dismissing the opinion of Democritus as to the origin of wind, he states that in his judgment wind may arise from four different causes. First; The earth itself breathes forth a vast amount of air from its interior, where there are large rivers and lakes, and where the moist air naturally gives rise to blasts of wind. Second; Long-continued evaporation carries the terrestrial emanations aloft, where the intermingling of the breath results in wind. Third; Much more important is the fact that the air in its very constitution possesses an innate power of motion; we cannot imagine that while we ourselves are endowed with a capacity of movement—and water has this power also—the atmosphere should be left inert and immovable (197). Fourth; Sometimes the sun is itself the cause of wind, when he loosens and expands the thick air (198).
In this enumeration allusion is made to one or two features of natural history which the author appears to accept as fact. He thinks there must be some vital force in water, otherwise it could not bring forth animals and plants, as we know it does. But not only water; fire, too, which devours everything, possesses this generative capacity, for, unlikely as it might be thought, it is nevertheless true that fire gives birth to some animals. The air, too, has some vital energy, as it alternately thickens, contracts, and expands, and rids itself of its impurities. The portion of it contained within the earth is asserted in a later part of the volume to be the source of the life of the vegetation at the surface (244).
The local winds, now known as “land and sea breezes,” are next discussed (198). Instead of the simple explanation which in our own day has shown these aerial currents to be beautiful examples of the results of diurnal variations of atmospheric pressure, the ancient theory represented that during the day the exhalations from the land are borne on high to supply the sun with nourishment, while at night, as they are not needed for that purpose, they accumulate until they have filled up a given space enclosed by mountains. When in such a space there is no more room, they move towards the quarter to which they can most easily escape; hence the wind. It is curious, however, to note that Seneca only describes the land breeze, which falls away as the morning advances. He does not specially refer to the equally characteristic sea breeze, which springs up after the other dies down, and continues during the day, until in the evening it is again replaced by the land breeze.
The important Etesian or northerly winds, with all their important local modifications in the Mediterranean basin, must have been a subject of constant observation to the Greeks and Romans. There was a general belief that as these winds reappeared regularly in summer, they were in some way connected with the position of the sun in the firmament. Seneca, after briefly stating this opinion, dissents from it on the ground that, as the sun reduces the strength of the morning or land breeze, it cannot be through his influence that the Etesian winds then begin to blow. But he does not explain how he would himself account for their occurrence. They are now known to be further illustrations of the influence of atmospheric pressure. In summer, when the hot region of the Sahara becomes a vast area of low pressure, the air streams into it from the north across the Mediterranean basin.
The account given of cloud winds (203) is an excellent illustration of the utter ignorance of the philosophers of antiquity of the very rudiments of meteorology, and, at the same time, of the confidence with which they offered their explanations of the phenomena of the atmosphere. Even now, after prolonged investigation, the laws that regulate the production of furious winds and gusts connected with clouds are far from being fully understood. The boldest meteorologist of to-day, with all his detailed experience, would hesitate to express his opinion as dogmatically as is done in the text. The idea that air accumulating either above ground or below acquires a vast disruptive force, obtained wide credence in early times. It was this pent-up accumulation which was supposed to burst clouds asunder and produce thunder-storms, while the same energy in caverns under ground led to earthquakes and the eruptions of volcanoes.
The occurrence of whirlwinds is explained by Seneca from the analogy of eddies in a river. As the water meets with impediments in its flow, it is driven back and made to whirl round before it can continue the onward current, so the wind, as long as it meets with no obstacle, sweeps on, but when it is thrown back by any projection in its course, or is collected together into a highly inclined narrow pipe, it whirls round upon itself like the eddies of a river. But the cause of the vorticose movement where there is no visible impediment is, of course, left unaccounted for.
In the fifteenth chapter of this Book a story is told of Philip of Macedon, who sent down a party of miners to examine an old mine. The men brought back to daylight a wonderful tale of vast caverns with high over-arching roofs, and filled with huge rivers and vast lakes. If the author’s intention was to connect the spaciousness of these underground chambers with the operations of ancient miners, he was sadly mistaken, since at no time has metal-mining led to the excavation of huge caverns; on the contrary, it has always been pursued in narrow shafts and passages. If the report brought back to the king was veracious, his emissaries had only come upon a series of natural grottos and tunnels, such as are of common occurrence in limestone districts, and which have no connection whatever with mining.117 But the narrative served Seneca’s purpose, since it furnished him with the occasion for a diatribe against the cursed love of gold, which had apparently been rampant in days long before those of Philip, and allowed him to supply from his own imagination some additional lurid horrors of the underground world.
When he gets back to his subject, he enters upon an enumeration of the various winds known to the ancients. He himself thinks that as the heavens are divided into twelve sections, so there are twelve distinct winds, not all felt everywhere, but never exceeding that number. He does not attempt, however, to account for them. In his reference to the names given to the various winds, he gives a quotation from Ovid’s Metamorphoses, in which the more conspicuous winds from the different quarters are mentioned. To this quotation he adds a line from Virgil’s graphic picture of the storm in the first book of the Aeneid, where Aeolus opens his cave and the south-east, south, and south-west winds rush out in fury upon the sea. Seneca remarks, in passing, that such a collocation of winds as Virgil enumerates could never have happened in a single tempest. The poet, however, has made no mistake. In a great cyclonic storm the wind veers round with the compass from south-east by south to south-west. And even if Virgil had added the north wind, which the philosopher says he left out, he would only have followed the invariable course of the winds in the cyclones of the northern hemisphere, which circle round towards the north as the storm area is passing eastward.
In conclusion, the author points out the teleological significance of the winds, and is thence led to repeat the time-honoured reproach against human iniquity which turns the winds from their beneficent intention to purposes of war.