Firstly, the origin of the winds. Aristotle rejects the view of Anaximander and the other Presocratics, that wind is air:
for the same air persists both when it is in motion and when it is still. Hence wind is not ‘air’ at all, for then there would also have been wind when the air was not in motion, seeing that the same air which formed the wind persists (565).Instead, he says that wind is caused by ‘dry exhalation’ and rain by ‘moist exhalation’ (evaporation) (566); it has a birth and a death, like a living thing, and this is caused by the sun and the moon (567). There are only two winds - the north and the south - because the sun travels from east to west and does not therefore touch upon the north or south, causing a build-up of clouds so that it rains when the sun approaches, and winds blow when the sun departs from the region (568). The north wind comes from the north pole, but the south wind comes from the tropics, as it cannot have the power to reach from the south pole into the northern hemisphere - this is why the south wind is warm.
The Aristotelian wind-rose (compass-card; see fig.127) explained at length in De Meteorologica was used as a model for all other wind-roses of antiquity, although, as Thompson reveals, many modern models of the wind-rose are incorrect (569), being based on the directional points N, NNE, NE, ENE, E, and so forth. Aristotle’s wind-rose was constructed from the position of the sun, rising and setting due east and west. North and south may then be added, and the subdivision of the quadrants to show the secondary winds must be extrapolated by the direction of that wind with reference to the sun, for example, Lips blows from the winter sunset, which is south-west. The position of the sun is determined from Athens, on latitude 38ºN; thus, the Aristotelian wind-rose would alter if set on a different latitude, for example, at Rome (32.5ºN). In any case, the notion of exact positions of winds is somewhat academic, given that the two types of people that would use a wind-rose - sailors and farmers - would only need rough ideas of the direction the wind would be coming from, and more importantly, they would need to know when the wind was coming. The wind-rose cannot describe the direction of seasonal winds like the Etesian-meltemi, sirocco and bora, or more local winds such as the leukonotoi or ornithiai. Sailors would also be travelling through many different latitudes, rendering the exact wind-rose useless; but for meteorologists and natural philosophers, Aristotle’s wind-rose was highly significant, surviving with small additions (mainly names of winds - for which see Pseudo-Aristotle’s De Signis, an account of the names and some of the properties of the cardinal, secondary and local winds) well into the medieval period.
The duodecimal classification of the winds seems to be Babylonian in origin, and Wood points to Homer as another source for its antiquity (570): the twelve colts sired by Boreas on Erichthonius’ mares (Iliad XX.225), and the twelve children of Aeolus (Odyssey X.1-76), although Homer only names the four cardinal winds in both books. It is probably a mistake to read too much into the numbers given in the Homeric epics, since in antiquity, numbers sometimes took on a particular significance - especially multiples of three.
In the Problems, Aristotle discussed certain questions and observations made regarding various subjects, and this is a rich source of information on proverbs (see below, section 4.8) and weather-lore connected to the winds. Some of the problems focus on the cause of different winds, for example, the Etesians:
Why do the Etesian winds always blow in their season and with such strength? And why do they cease at close of day and do not blow at night? Is this because the melting of the snow [at the north pole] by the sun ceases at eventide and the beginning of night? As a rule they blow when the sun begins to master and dissolve the ice in the north. When this begins, the ‘precursor’ [Prodroms] winds blow, and when it is melting, the Etesian (571).Aristotle thus concluded that Etesians are periodic because they are northerly (from the north pole) and thus closer to Greece, and because they blow in a period of still air (summer). The intermittent south winds are further away, blowing from the south pole, and they tend to rise in the spring, which is not a stable season for air masses, being full of moisture (572).
As with the Meteorologica, Aristotle writes that the winds arrive from directions in relation to the sun, from the summer sunrise or sunset. In addition, he describes the rising and the setting of the stars (especially Sirius) as having an effect upon the weather, frequently producing a substantial change (573) - this had already been noted by Democritus (see fig.126). He correctly links the equinoxes with a change in weather, observing that it brings the south-west wind and rain (574); the equinoxes do indeed exert control over the weather, with the moon and sun bringing their combined gravitational pull to bear on the tides, causing them to run higher and to thus produce a greater likelihood of storms, which, along with the high tides, can be extremely dangerous to shipping. Aristotle is also correct in his suppositions for a few more of the problems posed; for example, he writes that the south wind often brings rain because it collects moisture on its journey across the ocean (575). He understands the basics of convection (576), and also recognises that rain is produced from a concentration of clouds (577). Rather oddly, Aristotle insists that very high mountains have no wind, citing the example of Mount Athos as his proof: remnants of sacrifices left there one year are apparently discovered untouched the following year (578). This does rather strain credulity: Aristotle never went to Mount Athos to see this for himself, so possibly his informant was rather too enthusiastic in describing certain conditions. It is true that there is, at very high altitudes, less ‘air’ in the sense of oxygenated air, and winds are less powerful, being mainly the high-altitude Westerlies or the occasional storm - for example, in the Himalayas - but no mountain in Greece is high enough to experience these conditions. Mount Athos is 6439 feet high, outstripped by Mount Olympus, the highest mountain in Greece, at 9570 feet; the wind can, and does, blow on both peaks. Aristotle was perhaps inclined to believe his informant by a reference from Homer: in Odyssey VI.32, Athena travels back to her home on Mount Olympus, a place described as
Shaken by no wind, drenched by no showers, and invaded by no snows, [Olympus] is set in a cloudless sea of limpid air with a white radiance playing over it all (579).However, Aristotle could well be thinking of the Presocratic idea that held that winds came from clouds rather than from the upper atmosphere; mountain-tops are often shrouded in cloud, so it would stand to reason that there would be no wind above the clouds that create it.
Theophrastus’ De Ventis was written around 300 B.C. to amend and replace the works of Aristotle on meteorology, primarily De Meteorologica, although much of the information is taken from Problems XXVI. In addition to Aristotle, Theophrastus also used Anaximander and Anaximenes along with colleagues based around the Aegean for his more localised information, as well as sailors and farmers. His approach was somewhat more empirical than the methodology employed by Aristotle, and he rejects the theory of dry exhalation in favour of an amended version of the Presocratic idea of the wind as air in motion, leading him to a very basic understanding of atmospheric pressure. His work on local winds and sea-breezes shows an appreciation of the systems of convection and advection; and, like Aristotle, he was aware of the topographic changes forced upon the weather by geography, and also by orography (the study of mountains), of which his predecessor had been unaware.
Theophrastus remarks that the north and south winds are the strongest of all prevailing winds in Greece, blowing for the longest times; he attributes this to the air masses (controlled to a large extent by the sun) to the north and south, which is a fairly accurate observation (580). Their varying strength and heat are caused by the distance they have travelled, and what kind of land mass they have passed over (581), and he gives as an illustration the proverb noted in Aristotle (number 3, below in 4.8). Says Theophrastus:
North winds blow in the winter, in the summer, and in late autumn until the end of the season, while the south winds blow in winter, at the beginning of spring, and at the end of late autumn (582).This information is, of course, correct. He notes that the west wind blows only in spring and late autumn, and is both gentle and very ferocious, and can either nourish or devastate crops - hence its mixed reception in literature (583). He goes on to say that the leukonotoi are a kind of southerly meltemi (584), but they are more erratic and weaker because of the distance they have travelled across the sea. As for the meltemi proper, he repeats Aristotle (Problems XXVI 946a 10ff) in saying that they are caused by the melting of snow in the north during the summer (585). He adds an interesting note in section 13 on the severity of winters on Crete, and the increased snowfall on the island; long ago, he says, the mountain slopes were cultivable, even on Mount Ida. Theophrastus is thus aware of the cooling which heralded the change from the Sub-Boreal to the Atlantic periods.
His observations on winds led him to notice that during the day, they tend to quieten around noon. He attributed this to the scorching heat of the sun taking the power from the wind. Certainly he sees the sun, and heavenly bodies, as having a key role in the control of these elements:
the sun by rising seems both to set the winds in motion and to halt them... the moon has this effect also, but not to the same degree, being a kind of weak sun. Therefore the breezes are more powerful at night and the weather stormier at the full moon. And so, when the sun is rising, the winds now rise, now abate. It is the same with the setting sun; sometimes it halts the winds, sometimes it lets loose. The question whether these things happen in conjunction, as at the risings and settings of stars, must be looked into (586).Unlike Aristotle, who gives dry exhalation as the reason for the sun’s control of the winds, Theophrastus prefers not to commit himself if he is uncertain of the empirical cause. He has no such problem when he discusses ‘reversed’ (convectional) winds, the result of topography (587). His understanding of orography is also impressive:
There also occurs a backlash of winds so that they blow back against themselves when they flow against high places and cannot rise against them. Therefore the clouds sometimes move in the opposite direction to the winds, as in the neighbourhood of Aegae in Macedonia, when north wind blows against north wind. The reason is that when the winds blow against the high mountains near Olympus and Ossa and do not surmount them, they lash back in the reverse direction, so that the clouds moving on a lower level move in reverse direction (588).His knowledge of weather-conditions in the mountains, surely the result of some direct observation, continues in section 34 with an explanation of downdraughts creating squalls at sea, again an accurate observation of the phenomenon.
Theophrastus, like Aristotle, provides the reader with definite signs of the wind’s approach: waves, haloes, mock-suns, an obscured moon, and shooting stars are a few of the common heavenly indicators, while dolphins, cuttlefish and jellyfish are considered as reliable harbingers of strong winds (589). His proverbs are summarised from Aristotle’s explanations in the Problems, but he does also give credence to local sayings from around the Aegean which reflect local conditions, for example, the WSW wind at Cnidus and Rhodes brings heavy clouds and clearing weather very quickly, while the WNW wind brings clouds only, due to their directional nature (590). We should note that Theophrastus did not include a wind-rose in De Ventis; as a more empirical philosopher, did he realise the limited use it had? Or was Aristotle’s wind-rose considered satisfactory?
Between the advent of meteorology as a considered science with the early Presocratics through to Theophrastus, great steps were made in anemology. It is mainly the work of Theophrastus, who built upon Aristotle’s findings, that contributed most to the field, and with the study of natural philosophy of Rome, there is little that can be added by way of serious research. The Roman interest in anemology and meteorology was slow to begin, and did not reach its zenith until the works of Pliny the Elder and Seneca. The Epicurean Lucretius provides a good example of the earlier use of meteorology, which in his work De Rerum Natura tended towards the heavily poetic rather than the strictly scientific; thus his account of the seasonal year:
On came Spring and Venus, and her winged harbinger [Cupid] marching before, with Zephyrus and Flora a pace behind him strewing the whole path in front with brilliant colours and filling it with scents. Next in place follows parching Heat, along with Ceres his dusty comrade, and the Etesian winds that blow from the north-east. Next comes Autumn, and marching beside him Euhius Euan [Bacchus]. Then follow other seasons and winds, Volturnus thundering on high and Auster, lord of lightning (591).There are no Etesians at Rome! At the end of this passage, Lucretius becomes confused by his winds; the only season he has not yet mentioned is, of course, winter. Volturnus (wind ESE-SE) is a dry wind from the landmass of Asia Minor, while Auster is the south wind. Neither feature heavily during the winter months in the Aegean. But Lucretius was not the only poet to dabble with meteorology for the sake of his art; Catullus was equally guilty, but fared slightly better on the scientific front with these lines from poem XLVI:
Now the sweet gales of Zephyrus are hushing the rage
Of the equinoctial sky.
Vitruvius studied the winds in the hope of designing the most consumer-friendly city, which would be constructed in such a way as to exclude all draughts, thus making it a healthy place to live (see below, 4.7). His findings, collected in the De Architectura, include an octagonal wind-rose that follows the Tower of the Winds in Athens, built by Andronicus of Cyrrhus. This wind-rose (fig.128) utilises the sun for its calculations, like the Aristotelian model, but the result is somewhat different as the Vitruvian method relies on the shadows cast by the sun on a sun-dial rather than on the hypothetical line of the equinoctial sunrise and sunset. He adds that there are only eight winds, and this is because, following the measurement of the earth’s circumference (31,500,000 paces) by Eratosthenes, it was revealed that the wind "seems to occupy... 3,937,500 paces" (592). One should not, then, wonder if the wind goes through many different changes as it travels through space. He goes on to name twenty-four winds, cardinal and subsidiary (593). Vitruvius also notes that there are convectional breezes, caused by the rising of the sun, its heat thrusting away the moisture of the night (594).
Pliny the Elder, in his Natural History, wrote on the causes of winds, taking as his lead both the Presocratics and Aristotle. Storms, he believed, were caused by falling stars reacting with clouds - thus creating thunder, lightning and whirlwinds (595). He does not favour nor put forward any new theory on the physical cause of wind, and follows Theophrastus’ observations on topography, adding his own examples of strange happenings: wherever wind can be reflected back from a solid object, like a cavern wall or a valley, echoes can be produced, and certain other peculiar things, such as:
[a cavern] on the coast of Dalmatia, from which, if you throw some light object into it, even in calm weather a gust like a whirlwind bursts out; the name of the place is Senta. Also it is said that in the province of Cyrenaica there is a certain cliff, sacred to the South Wind, which it is sacrilege for the hand of man to touch, the South Wind immediately causing a sandstorm (596).The coastal cavern may, of course, be open to the sea at the base of the cliff and would therefore operate as a blow-hole, cool air rushing up when high tide or heavy seas push into the base of the cavern. The sacred cliff would seem to be some local lore; hardly surprising given that Cyrenaica would be subject to sudden and brutal sandstorms, the simoom, throughout the summer months especially. Pliny’s wind-rose is ultimately the same as Aristotle’s, the slight deviance made by Vitruvius more or less ignored in favour of the original Greek model, which continued to be popular with the Romans. However, Pliny added four more winds to the list, subsidiary local winds that blow in the provinces with enough force to merit inclusion on the Roman wind-rose (fig.129).
Seneca’s Natural Questions takes as its source the lost work of Posidonius, although he does not hesitate to paraphrase Aristotle; he writes that wind is air in motion but not in the Democritian sense (597), but rather like dry exhalation (598) and by the Presocratic notion of evaporation (599). He attacks the notion of the meltemi being caused by melting snow (600), but advances no alternate theory. His wind-rose is the Roman version of Aristotle’s, with sixteen rather than twelve winds, and the names he assigns to the winds and the quarters from which they blow agrees with Pliny’s work (fig.129).
Favorinus’ natural philosophy is known to us through Aulus Gellius’ collection of extracts from other authors, the Noctes Atticae. In book 2, he recounts a time when Favorinus was attending a dinner party, and he is asked where the wind Iapyx comes from (it is mentioned in "a Latin poem", probably Horace Odes I.3.4 or III.27.20). Favorinus will tell all, since "there was no general agreement as to [the] designations, positions or number [of winds]" (601). He follows the Aristotelian wind-rose in many respects, inserting Roman names in addition to Greek, and, contra Aristotle, maintains that there is only one true north and one true south wind while all others are variants on the east and west. He also goes on to name a few local winds, Iapyx (Apulian, from the River Iapygae (602)) amongst them. Favorinus says that he has drunk rather too much to explain the Etesians, but remarks that one Publius Nigidius wrote a treatise On Wind in which he stated that "Both the Etesians and the annual southerly winds follow the sun" (603), although the philosopher is hardly sure what Nigidius meant by this remark. One imagines that he was influenced by the thought of Theophrastus (De Ventis 15-17), who proposed that the sun was the main agent in the creation and control of the winds, particularly the stronger winds like those from the north and south.
Roman philosophers, then, seem to have agreed to follow the Greek model for anemology, with few changes made to the initial workings of the weather and to the wind-rose. Local winds, especially in the provinces, replaced the more local of the Greek winds (Gallic Circius instead of Greek Sciron at WNW, for example), and there seemed to be an interest in the etymology of the names of winds, something which continued until the seventh century A.D., when Bishop Isodore of Seville published his Etymologies, including a short section on the winds derived in the main from Pliny, although he does quote verses from Lucretius and Virgil (604). It would probably be safe to say that, despite Seneca’s few complaints on credibility, the Romans were only too pleased to leave the finer workings of meteorology to the Greeks; they were more concerned with the practicalities afforded by the winds, as will be seen in the following sections.
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