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] [115] The various ancient interpretations of the cause of the Nile’s annual rise are succinctly given by Lucretius (_De Rer. Nat._ vi.
712–37), but he does not indicate a preference for any one in particular, though he devotes most space to the influence of the Etesian winds.
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.
[116] This view hardly agrees with what is expressed in Book II. (60, 61), but it more accurately expresses the fact.
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.
BOOK V 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.
[117] It is possible that these ancient mines were driven in search of metal seams or veins traversing limestone, like those of lead among the caverned limestones of Derbyshire.
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.
BOOK VI This is, perhaps, the most valuable part of the volume, for it contains more of the author’s own observations than the rest of the work. It deals more particularly with the great earthquake of 5th February A.D. 63, which occurred in his own country, and about which he could collect information at first hand. As already mentioned, the subject of earthquakes had long fascinated him, and he had published, in his youth, a volume about it. The calamity which brought so much injury to the towns of Campania was more especially likely to enlist his vivid interest, for the region that had been convulsed was with him a well-known and favourite part of Italy, where he often came to spend, on the shores of the Bay of Naples, such leisure as the life in Rome allowed him. Besides, it was the native district of Lucilius, to whom the volume was addressed, and whose town of Pompeii had suffered from the shock.[118] Hence he here plunges at once into details of the damage caused by this particular earthquake. As a prelude to his inquiry into the whole question of the origin of such catastrophes, he indulges in reflections on their appalling nature. Some of the unfortunate residents in the convulsed district had fled from it, vowing never to return. But where, the writer asks, can they be sure of safety, seeing that no quarter of the world is exempt from this form of danger? He urges that it is at least some consolation to be assured that such calamities are not the work of angry gods, as was popularly believed, but are traceable to their own special causes in the processes of nature (228).
[118] In Seneca’s letters, frequent reference is made to his visits to the district. He seems generally to have taken a villa at Baiae, or some adjacent place on that western part of the coast. He appears to have been a poor sailor, glad to make for the nearest landing-place between Baiae and Naples, so as to escape from the pangs of sea-sickness. On one of his excursions he revisited Pompeii, and was set into a reverie of his youth there. See his _Letters_, 49, He then considers the various opinions entertained on this subject by earlier writers, which, on the whole, he regards as crude and inexact.
The cause of earthquakes had been found in water, fire, air, and the earth itself, or in a combination of several of these agencies, or even in the co-operation of the whole of them. As regards the action of water, he dismisses the opinion of Thales (231), but in the statements of other authors, who maintain the power of internal water in causing earthquakes, he sees a greater probability of truth. He fully admits the existence of large rivers and extensive lakes inside the earth, and that in these dark uninhabited regions flooded rivers undermining their banks, and a swollen sea lashed into fury by the subterranean winds, may communicate shocks to the surface of the earth (234).
That fire is the origin of earthquakes had been held by various philosophers, who, however, differed as to the manner in which the fire acts. Anaxagoras thought it was by explosions caused from the collision of underground clouds (236); others held that the immense mass of vapour produced by the subterranean conflagrations as it accumulates may exert such a pressure as to disrupt all obstructions; or when the pressure is less may cause no more than a heaving of the surface. The idea that the shock of an earthquake results from the removal of material underneath, whereby the stability of the overlying portion is undermined, and a collapse of the ground ensues, was held in various forms. Some thought that this destruction arose from extensive combustion within the earth. Anaximenes supposed that just as at the surface, rocks and old buildings yield to the ravages of time and fall down, so in the interior of the earth similar landslips may occur and cause shocks to the districts above them (237).[119] [119] The collapse of the roofs or sides of underground caverns may undoubtedly be in some instances the cause of local earthquakes. This origin is enforced by Lucretius: terra superne tremit magnis concussa ruinis, subter ubi ingentes speluncas subruit aetas.
But the favourite opinion of antiquity regarded earthquakes as primarily due to the violent commotion of air. Seneca comments on the views of various philosophers, and more especially Aristotle’s, as to the way in which the air acts, and he then proceeds to deliver his own judgment. He has no doubt that, though some of the other agencies may co-operate, the chief motive force in earthquakes is air. By no part of nature, he affirms, is such violent energy displayed as by air; it kindles fire, tosses the surface of the waters into waves, destroys large tracts of the earth, uplifts new mountains, and raises in the midst of the sea islands never seen before. Not only does air exist above ground, but it also fills the hollows and interstices of the interior of the earth, into which it freely enters from the surface.
Nothing in nature is so restless as air, and the earth cannot but be affected by the movements of the air included in its inside. The author agrees with the general opinion that when the air begins to be agitated in a subterranean cavern which it has filled, pressed by that which is still entering, it struggles to escape, and, when it does so, emerges with a violence proportionate to the narrowness of the passage for its exit. But if unable to make its way out, it becomes furious, acts like a swollen impetuous river, and that overthrows everything in its path.[120] [120] Lucretius gives a picturesque recital of these views (_De Rer.
Nat._ vi. 535–607).
It is not difficult to realise how this explanation should have been accepted in antiquity, and should have held its ground down even into modern times. The violence of the commotions of the atmosphere was a familiar feature on the surface of the earth, although its physical causes, variously guessed at, were utterly unknown. To minds that had no conception of the very rudiments of meteorology, there seemed to be no reason why air inside the earth should not be affected by as violent hurricanes as the air outside. And as such hurricanes were the most powerful natural agencies known, their action was not unreasonably invoked to account for the phenomena of earthquakes. Assuming that the air in a large subterranean cavern would behave as the free open atmosphere does, the old philosophers did not find themselves under the necessity of explaining what was to set the air in motion within the subterranean recesses and lash it into fury there, any more than they had to account for tempests above ground.
Obviously, if the air found its way from the outside into the internal parts of the earth, it must have had equal facilities for egress. And in the convulsions of an earthquake it might be supposed to issue with violence through some of the previous openings or from the rents made at the time. In corroboration of the truth of the prevalent opinion, it was asserted that after an earthquake air was found to issue from the ground, but no account appears to have been preserved of any violent outrush of air. As a further evidence that it is to the force of air that all these internal disturbances are due, the author remarks that after a violent earthquake another shock of equal violence cannot occur, because the first has opened a passage for the struggling winds.
The progress of investigation has, in modern times, thrown a flood of light on the phenomena of earthquakes, though there still remain many problems in the subject which await solution. It is needless to say that no foundation whatever has been found for the ancient faith that the air plays the chief part in these subterranean commotions.
Seneca discusses the nature of earthquake motion. He recognises three kinds of movement--quaking (_succussio_), tilting (_inclinatio_), and trembling (_vibratio_)--and he gives illustrations of the kind of causes to which they may be referred (252). He believes that the extent of country convulsed by an earthquake depends upon the area of the subterranean cavern in which the wind performs its exploits, and as these internal cavities do not continuously underlie vast tracts of the earth’s surface, no large spaces of that surface are simultaneously shaken. In his day there appears to have been no record of a shock affecting the whole basin of the Mediterranean Sea. He thinks that no earthquake ever extends as much as two hundred miles. He cites the recent calamity in Campania, which did not pass beyond that district, though marvellous tales about it had spread far and near, and he gives other examples of the markedly local character of the phenomena, so far as then known. He affirms that maritime districts are those most frequently shaken (255, 257), in proof of which he gives various instances, including the late disaster to Pompeii and Herculaneum in a region which had never been known to be shaken before.
He had received information about the Campanian shock, and the narrative in which he embodies it has the interest of being the most detailed account of an earthquake that has come down to us from antiquity. First of all, as already mentioned, he states that the movement was confined to the district of Campania, no mention being made of its having been felt even so near as Rome. He notices the injury done to Herculaneum and to Naples by the damage of public and private buildings; bronze statues were split open and some people were driven out of their minds. He records that Campania continued to tremble for some days after the great shock. He had heard that a flock of six hundred sheep was said to have been killed near Pompeii.
Accepting the report as true, he sees no reason to suppose that the animals died of fright, but thinks it not unlikely that they were poisoned by the ascent of pestilential vapours from the ground. This conjecture of his receives perhaps some support from the fact that in this volcanic district, after an eruption of Vesuvius, so much carbonic acid gas has been said to escape from the ground as to suffocate hundreds of hares, pheasants, and partridges. But the most vivid experience of the earthquake which he narrates is that of a grave philosophic friend who, when in his bath, saw the tiles of the floor separate from each other, allowing the water to sink through the opened joints, while the next moment, as the pavement closed again, the water was forced out all bubbling. A better illustration of the transit of a wave of shock could not be desired.
Seneca was prepared to believe that great changes had been wrought by earthquakes on the face of the land. He cites in support of this view some remarkable examples which had occurred within the times of human history, such as the sinking of the towns of Buris and Helice, the disappearance wholly or partially of the island of Atalanta, and the subsidence of Sidon (256). He refers also to various striking features of landscape in different regions which had been popularly assigned to the work of earthquakes, such as the separation of Ossa and Olympus, the disruption of Sicily from the Italian shore, and the severance of Spain from the continent of Africa (263).
That the phenomena of earthquakes are closely connected with those of volcanoes was the general belief in antiquity, and continued to be accepted up to the middle of last century. It was believed in early days that just as the collision of clouds during storms produces the fire seen in lightning, so during the tempestuous agitation of the air within the earth, such heat is generated as to set fire to beds of sulphur or other combustible materials, and thus that rocks are melted and are forced up to the surface by the vast energy of the escaping air.[121] It is to be regretted that Seneca has not left an account of his own opinions on this subject, but from the allusions in the present treatise he may be inferred to have held the prevalent opinion. He alludes in various passages to volcanic eruptions that had taken place in his own time, or not long before, in the Mediterranean basin. An eruption of Etna is briefly noticed, when the mountain was in violent eruption, ejecting such a quantity of fine burning sand and dust as to turn day into night, accompanied with much thunder and lightning (77). This may have been the eruption alluded to in similar language by Cicero, who adds that for two days nobody could see his neighbour.[122] Seneca further cites two eruptions in the Aegean Sea, one of which had taken place in his own time, when a new island was upraised “by the force of air.” He alludes to Thera and Therasia, and the interesting account given by Posidonius of the uprise of an island in the same sea, with attendant circumstances closely resembling those of the eruptions at Santorin in modern times (73, 252). According to Asclepiodotus, the fire, after overcoming the resistance of the thick mass of sea, shot up above sea-level to a height of two hundred paces.
[121] This view of the nature of volcanic energy is graphically expressed by Lucretius (_op. cit._ vi. 639–702).
[122] _De Nat. Deor._ ii. 38. See also Lucretius (_ib._ vi. 641), who describes the more conspicuous features of an eruption, and concludes with the line ne dubites quin haec animai turbida sit vis (693).
From a consideration of the causes of earthquakes the author is led by his accustomed train of thought to draw the ethical lessons which the subject suggested to him. He repeats his belief that against the perils of earthquakes, as against all the other dangers and fears of life, the only assurance is to be obtained from elevating studies and a contemplation of nature (265). It matters not when or in what form we shall quit life, whether from some trifle or from a world-wide catastrophe. To be happy without fear of anything that may befall us, we must carry our life in our hands, steeling ourselves against fear, and prepared even to welcome death as the advent of a friend.
BOOK VII After a brief introduction, marked by no little elegance and literary skill, the author introduces the subject of the heavenly bodies, and more especially of Comets which he is to discuss in this Book. He proposes at the outset to endeavour to ascertain whether the earth stands still while the universe revolves round it, or if it is the universe that remains at rest while the earth revolves. But he is led on from one topic to another, without having arrived at a definite solution of this problem when the volume comes to an end. From various expressions, however, it may be inferred that he adhered to the primitive belief that it is the universe which goes round the earth.
Thus in Chapter IX. he speaks of the movement that drags the universe along and asks what is swifter than that revolution (281). The heavenly bodies may not stand or turn aside, they all move onward with the irrevocable movement of this eternal creation (299).
The opinions of various philosophers on comets are quoted and criticised. He is especially severe in his comments on Epigenes, who thought that comets are produced somewhat as fires are excited by whirlwinds. The Greek threefold classification of comets is cited, and then Artemidorus comes in for his share of vituperation; to disprove his theory of the firmament being a solid roof to the world would be, in the author’s opinion, nothing but beating the air. Ephorus fares no better, being briefly dismissed as often deceiving and often deceived.
Apollonius of Myndus held that many comets are distinct planetary bodies, which wax and wane like the planets, being brightest when they are nearest us and growing dimmer as they recede to a greater distance. But Seneca refuses to admit that they have the character of true planets; in his view they are insubstantial irregular fire (291).
But he does not agree with his Stoic brethren in regarding them as generated in dense air and pursuing their course according to where they can find fuel to sustain them (292–4). He conceives that they are not mere sudden and transient fires, but belong to the eternal works of nature. They steadily traverse their course, and he can understand that they may have such wide orbits as to carry them far beyond the limits of the Zodiac (296). He can see no reason why the five planets then known should be the only stars that move across the sky, though others had not yet been discovered. Astronomy, he remarks, is in its infancy, many mysteries of nature remain still to be discovered, and the day will come when posterity will marvel at our ignorance of things which will then appear to be so evident. Some future observer will demonstrate the paths of the comets, why they wander so far from the other stars, and what is their size and constitution. We may be content with what we have found out, and leave something for posterity to discover.
In a tone of sad pessimism he brings his volume to a close. From a contemplation of the glories that might be achieved by mankind in searching out the marvels of creation he turns to his own age and his own country, only to see on every side proofs of decadence. No one now cared for the pursuit of wisdom. Philosophy and every liberal study were neglected. The schools of philosophy were dying. If his countrymen even now would set themselves with all their energy to the task, if the young would give their sober attention and the elders would teach them, they would scarcely succeed in reaching the bottom of the well in which truth lies. Meanwhile they were searching merely on the surface of the ground and with but a slack hand.
NOTES BY TRANSLATOR “AIR” The word “air” occurs in the text over 200 times, but not always as a translation of the same Latin word. With a term so elastic and so ambiguous it would have been mere pedantry to attempt a uniform rendering; and indeed such uniform rendering would have been more misleading than the course adopted of rendering according to the context, which the idiom of our language seemed to demand.
Seneca has two main terms for air--_aër_ and _spiritus_. _Aër_ means, generally speaking, either air generically, or the atmosphere specifically. _Spiritus_, on the other hand, denotes air under certain conditions of tension, or strain, or pressure, when it is capable of exerting force or violence; to its influence are attributed many effects due in reality to gases, or other causes. On p. 52, l. 1, we have the definition “air (_spiritus_) is the atmosphere (_aër_) in violent motion”; and on p. 205 the concluding words of V. xiii. are “air differs from wind in degree alone. A more violent air is a wind; air in turn is gently flowing atmosphere,” where again _spiritus_ is Again, in the _Aetna_, l. 212, we read, “The winds when inflated are called _spirit_; when in subsidence, _air_” (Professor Ellis’s translation), where the same terms _spiritus_ and _aër_ are employed.[123] [123] For a discussion of the meaning of the term _spiritus_ and the parallelisms in its use by Seneca and the author of the _Aetna_, see Professor Ellis’s edition of that poem, Prolegomena, pp. xl-xliii.
Now if our author had been consistent in the use of the words, there would have been a strong case for a uniform adoption of “air” and “atmosphere,” whenever they occurred. But numerous passages might be cited to show that he interchanges the words without apparent motive, just as we do “air” and “atmosphere.” For example, on p. 69, l. 2, “So fire will pass into air (_spiritus_),” while on p. 71, l. 9, “the air (_aër_), which is interchangeable with fire.” Again, on p. 75, l. 6,