Header Ptolemy


In A.D. 79, the Romans, coveting wealth, prepared to throw mankind once more into uproar. The general Gnaeus Julius Agricola made plans to complete the conquest of Britain. Wales had been subdued in the previous year. In A.D. 80, he marched into Scotland.

Britain, the largest island known to Rome, lay at the edge of the Oikoumene, with its northern shores washed by the wastes of the World-Ocean. Mediterranean geographers reported that the skies there were overcast, with constant rain, but the cold was not severe. Summer days in the north of Britain were long beyond the measure of the Mediterranean world. The nights were a brief interval between twilight and dawn. Some said that in Scotland the Sun was visible throughout the night in summer: “it does not set and then rise again, but simply passes over...the flat extremities of the earth with their low shadows do not project the darkness, and nightfall never reaches the sky and the stars.”

Scotland haas been rotated about 90 degrees. Ptolemy’s information about the north of Scotland may have come only from Agricola’s fleet.

These northern regions, though mysterious, were not unknown. The Greek explorer Pytheas had sailed north of Scotland about the year 325 B.C. Livy (born in 59 B.C.) wrote an account of Britain in his lost 105th book, and the Orkney Islands were known to Pliny and Juvenal. Agricola, however, was the first to demonstrate the insularity of Britain. In A.D. 84, after he had overrun Scotland, his fleet circumnavigated the northern coast, surveyed Orkney and Shetland, and returned 'favoured by weather' to their harbour of Truculum (perhaps Loch Broom). They reported that the Ocean north of Britain was “sluggish and heavy to the oar and comparatively torpid even to the wind...because land and mountain, the cause and occasion of storms, are fewer and further between, and because the deep mass of uninterrupted water is slower to be set into motion.”

Unfortunately, the official fleet's achievement had been pre-empted by a gang of mutineers. In A.D. 83, a cohort of German Usipi murdered their centurions, captured three galleys, and sailed from the Clyde. They struggled slowly up the west coast and round the north of Scotland, fighting several battles along the way and being reduced by starvation to cannibalism. Having rounded Britain, the battered galleys made their way across the North Sea to the coast of Germany, where they were wrecked. There was no hero's welcome. The mutineers were regarded as pirates, and put to death or sold as slaves.

In A.D. 84, Agricola, about to complete the conquest of Scotland, was recalled. According to the sixteenth-century Scottish historian Hector Boece, the night skies of Caledonia blazed with portents just before his departure. A shower of stones and another of frogs fell in Athol. On clear nights, a ship was seen in the sky, moving fast. All one winter night, the air blazed with wondrous flames; “high in the air...there raged a burning fire, as if knights in armour and on foot fought with great force”. If these night sky fires ever actually happened, they were almost certainly displays of the northern auroral lights, but, as usual, there are grave doubts as to their historicity. Hector Boece, according to modern students, was over-fond of marvels, and did not hesitate to invent when sources failed him. Modern historians, however, preoccupied with the affairs of humanity and often unaware of what can be seen in the sky, may react with excessive prudishness to accounts of aerial portents, and it must be said that that Boece's nocturnal fire is a tolerable description of a fiery aurora borealis.

Tacitus, Agricola's biographer and son-in-law, makes no mention of sky fires or any other portents during the general's stay in Britain. There is a curious passage in his Germania, where he describes the sluggish sea to the north of Germany, 'with which the earth is girdled and bounded'. Here, “the last rays of the Sun...remain bright enough from his setting to his rising again to dim the stars: popular belief adds further that the sound of his emergence is audible and the forms of his horses visible, with the spikes of his crown.” E. H. Warmington said, “The halo round the sun's head or 'the spikes of his crown' are sometimes explained as interpretations of the Aurora Borealis. 'The forms of his horses' rather tends to discredit such rationalism.” It is probably a description of the northern midsummer twilight.


In A.D. 96, the sage Apollonius of Tyre, still going strong, was in Athens. The Sun was obscured. According to Philostratus, “the orb of the Sun was surrounded by a wreath which resembled a rainbow, but dimmed the sunlight.” The governor of Greece, 'afraid lest night should ensue and swallow up everything' summoned Apollonius to Boeotia, to ask his opinion of the portent. 'Be of good cheer', Apollonius told him, 'for there will be some light following such a night as this.' On September 18, the emperor Domitian, a sullen tyrant, was assassinated.

The two solar eclipses of A.D. 96 (May 10 and November 3) were in South America and the Pacific Ocean. Philostratus implies that the solar obscuration was seen over a wide area of Greece, and that it was still continuing when Apollonius spoke to the governor. Philostratus' description is clear. The Sun was dimmed, and around its disc there appeared rings of coloured light. An exactly similar appearance was seen after the eruption of Krakatoa in 1883. The Sun was obscured, and was surrounded by a ring of red and silver light.

If Apollonius' obscuration was caused by high-level dust from a distant volcano, then where was the volcano? It is tempting to suggest that it was in Cornwall. The seventeenth-century historian John Sellar reports that in A.D. 96, just before the death of Domitian, 'a terrible Tempest and Earthquake happened' in Britain. In Essex, a great sea flood destroyed 'many Villages, Towns, People, and Cattel; and Ebbing again, left many Monstrous Fishes on the Plains.' At the same time, in Cornwall, 'Flames ascended out of the Ground'. Britton says, rather sniffily, that all these events 'appear to be quite imaginary', and he is probably right, although the question remains as to why John Sellar should have wished to sully his history with the imaginary.

The elderly Nerva, who succeeded Domitian as emperor, died on January 27, A.D. 98. The historian Aurielius Victor, about A.D. 360, claimed that there was an eclipse of the Sun on the fatal day, but this also must be imaginary. The nearest eclipse to the date was one in the Arctic on March 21. Perhaps Apollonius' obscuration was still continuing.
Geologic disturbances in the west of England were still continuing, according to Dr. Short. In Somerset, 'a city was swallowed up, name and all' by an earthquake in A.D. 103.


In A.D. 115 the emperor Trajan was spending the winter in the Syrian city of Antioch, resting after eastern campaigns which had enlarged the Roman Empire to its greatest physical extent. The Empire now possessed the provinces of Dacia, Armenia, Mesopotamia and Assyria, and Trajan possessed the treasure of the Dacian king Decebalus. Decebalus, foreseeing defeat in A.D. 105, had used prisoners of war to divert the river Sargetia, which flowed past his palace, and had concealed his gold and silver in an excavation beneath its bed, afterwards allowing the river to return to its original course. Unfortunately the king's companion Bicilis, captured by the Romans, revealed the hiding-place.

Antioch, 'the third city of the world for beauty, greatness, and population', was thronged because of the presence of the emperor. Soldiers, businessmen and tourists from all parts of the Empire were sightseeing, despite the windy weather and frequent thunderstorms.

The sound of the earthquake came first, 'a great bellowing roar'. It gave a few moments' warning, but those moments were not enough. The earth heaved up and down, throwing buildings, trees and people into the air, and the buildings fell back as wreckage. The warning sound of the shock was drowned in the grinding crash of universal collapse. A vast cloud of dust billowed into the sky. Outside the city, the summits of Mount Casius sagged and slid down. Other hills were levelled. Water burst from the earth, while some streams disappeared.

Antioch was a ruin, but the earthquake was not over. Lesser shocks continued for several days, forcing the survivors, including the emperor Trajan, to retreat to the open space of the city's hippodrome. Trajan, slightly injured, had escaped through a window when the shock struck. Later the story was put about that 'some being, of greater than human stature, had come to him and led him forth'.

Meanwhile, those who had been trapped in the ruins of their houses called for help in vain. Some were killed by aftershocks. Others remained, suffering terribly from hunger and thirst. Those who had escaped refused to return until they were sure the earthquakes were over. “When at last the evil had subsided”, Dio says, “someone who ventured to mount the ruins caught sight of a woman still alive. She was not alone, but had also an infant; and she had survived by feeding both herself and the child with her milk. They dug her out and resuscitated her together with the babe, and after that they searched the other heaps but were not able to find in them anyone still living save a child sucking at the breast of its mother, who was dead. As they drew forth the corpses they could no longer feel any pleasure even at their own survival.”

The year after the earthquake, Trajan visited Babylon. There he looked once more into the earth, and saw death issuing from the depths. He saw one of the deadly 'breathing holes' mentioned by Pliny, a chasm from which a lethal vapour emerged, fatal to 'any terrestrial animal and any winged creature that so much inhales a breath of it'. Perhaps there he considered his behaviour at Antioch, which seems to have been less than heroic.

Trajan then turned with relief from the mysteries of the inner earth to military affairs. In A.D. 116 he conquered Mesopotamia and captured the Parthian city of Ctesiphon. Then he journeyed down the Persian Gulf, so that he might set eyes upon the World-Ocean. Dio says, “Then he came to the ocean itself, and when he had learned its nature and had seen a ship sailing to India, he said; 'I should certainly have crossed over to the Indi, too, if I were still young.' For he began to think about the Indi, and was curious about their affairs...”
Trajan stood upon the shore of the World-Ocean and gazed yearningly towards the mysterious East: but his footprints marked the uttermost expansion of the Roman Empire. Soon he turned back, and the Empire retreated with him.

Ptolemy map
THE INHABITED WORLD, according to Claudius Ptolemy (circa A.D. 150).
The inhabited world was about 40,000 stadia wide and 72,000 staria long. In longitude it occupied half of the Northern Hemisphere. The circumference of the Earth was 180,000 stadia.


A few years after, the last great scientist of the ancient world offered his view of an unified universe. Claudius Ptolemy was born at Ptolemais in Egypt, about A.D. 100, and made his astronomical observations 'from the parallel of Alexandria' between A.D. 127 and 151. He was the first astronomer to construct a theory of the solar system that accorded almost exactly with observation.

The two basic tenets of ancient astronomy were that the Sun, Moon, planets and stars revolved around the Earth, and that they performed those revolutions in perfect circles. The first accorded with observation. The second was an assumption based on an assumption. Heavenly bodies were perfect, therefore they must move in a perfect geometrical figure, the circle. Some astronomers, such as Aristarchus of Samos, were willing to have the Earth and planets revolve about the Sun, but even they would not give up their circles. Ptolemy said, “the motion of the heavenly bodies is the most unhampered and free of all motions, and freest motion belongs among plane figures to the circle”.

Unfortunately, what was seen in the sky did not accord with the theory of circles. The planets Venus and Mercury refused to leave the vicinity of the Sun, as they should were they moving in a perfect circle about the Earth. The planet Mars seemed to revolve about the Earth, but it moved erratically. Sometimes it halted in its west to east course through the sky, then moved retrograde with increasing speed, slowed down, paused again, then resumed its original path. The planets Jupiter and Saturn did the same thing.

Ptolemy saved the circles by adding circles. The planets, as well as moving in a circle about the Earth (the deferent), moved in a smaller circle (the epicycle) about a point on the deferent. The epicycles of Mercury and Venus were centred on a point on their deferents which was always in line with the Sun.

The saving of the circles was so satisfactory that Ptolemy ignored one awkward point. The planets no longer revolved around the Earth, but around an empty point on their orbit which itself circled the Earth. He might have made things simpler by having the Sun revolving round the Earth while the other planets circled the Sun, but it seems he was reluctant to deny the Earth pre-eminence. The points in the void about which the planets circled at least were attendant upon the centre of the universe.

Unlike Pliny, Ptolemy believed that the Earth was stationary. He accepted that the spherical Earth was infinitesimal in size when compared to the dimensions of the universe, but he preferred to have the sphere of stars revolve with unthinkable velocity rather than have the Earth rotate once a day. He described the idea of the Earth';s rotation as 'ridiculous' and 'unnatural'. If it revolved, “neither clouds nor other flying or thrown objects would ever be seen moving towards the east, since the Earth's rotation towards the east would always outrun and overtake them”.

Ptolemy organised the solar system in his treatise Syntaxis Mathematica, later called the Almagest. In the Tetrabiblios, he codified astrology. In the Manual of Geography, he summed up the Earth.
“The Earth” he said, “may be divided into four by the equator and a meridian; the inhabited world is approximately contained in one of the two northern quarters”. Latitudes (distances from the equator) of places on the Earth's surface could be established by measurement of the longest day. The most southerly inhabited places were Agisymbia of the Ethiopians and Taprobane. In Taprobane the longest day lasted 12 hours and 45 minutes. The northernmost zone of habitation was Thule, where the longest day was 20 hours. When drawing his map of the world, Ptolemy marked lines of latitude at places where the length of the longest day differed by a quarter of an hour. The meridian of longitude must be fairly arbitrary. Ptolemy chose the Fortunate Isles, the ultimate west of the known world, and drew longitudes a third part of an equinoctal hour apart. The known world spanned 12 hours, and so had 36 longitudinal lines. Ptolemy believed that the known world covered 180 degrees from the Fortunate Isles to Sera and Cattigara in easternmost Asia, and thus exaggerated Asia into the middle of the Pacific Ocean.

Ptolemy said that the boundaries of the known world were “on the north, the ocean which surrounds the British Isles, the north parts of Europe and the unknown land (terra incognita) in the northern region of Asia; on the south, the unknown land which encloses the Indian Sea, and the unknown land to the south of Libya and Ethiopia; on the east, the unknown land which adjoins those eastern nations of Asia, the Sinae and the peoples of Serica, the silk-producing land; on the west, the great Western Ocean and unknown parts of Libya.” He departed from the idea of a world-encircling Ocean by making the indian Ocean a vast salt-water lake, like a larger Mediterranean. At the easternmost end of the Indian Ocean is the Great Gulf (Sinus Magnus). A South American writer suggested that the Great Gulf is actually the Pacific Ocean, and the land on its far side is Peru. O. A. W. Dilke, author of Greek and Roman Maps, remarked, 'Although such a theory should not be dismissed out of hand, it is open to serious objections'.
Ptolemy turned from his studies of the Earth and the universe to the weather of his home town. He kept the first known meteorological diary, probably in Alexandria, about the year A.D. 120. He recorded rain in every month except August, thunder in all the summer months, and frequent days of great heat in July and August.




Meanwhile, at the eastern end of the known world, in China, practical work was being done. In A.D. 132, Chang Heng, mathematician, geographer, and director of astronomy, invented his hou feng ti tung i or 'earthquake weathercock'. He made a bronze vessel, six feet in diameter, ornamented with designs of mountains, animals, and ancient characters. Outside the vessel, eight dragons each held a bronze ball in its jaws. Before each dragon sat a toad with its mouth open. When a shock came, a pendulum inside the vessel vibrated, opening a mechanism in the jaws of one of the dragons. The ball fell into the mouth of a toad, and the mechanism locked itself. Observers of the Bureau of Astronomy then deduced the direction of the earthquake by the orientation of the empty dragon.

The scholars of the capital Lo-Yang were amazed at Chang Heng's ingenuity. One said, “Nothing like this had been heard of before since the earliest records” and claimed that there was 'an almost miraculous agreement' between the seismograph's indications and the news of the actual shock. One day in March of A.D. 138, a dragon let fall a ball even though no tremor had been felt. The officials of the Bureau of Astronomy scratched their heads, until, several days later, a messenger arrived to report a severe earthquake in Lung-Hsi (Kansu), 400 miles to the west. After this, 'everyone admitted to the mysterious power of the instrument', and observers were charged with the duty of recording earthquake directions.

The earthquake records of China were the most extensive in the world. The Shu Chi Chheng encyclopaedia had six chapters devoted to
descriptions of earthquakes. Among the earliest was one in 780 B.C., when 'in the reign of King Yu (of Chou), the three rivers of the western province were all shaken and their beds raised up.' Earthquakes were also portentous. After the 780 B.C. Shock, one Poyang Fu announced bluntly, 'The dynasty of Chou is going to perish...the Chou will be ruined before ten years are out'. A thousand years later beliefs were unchanged. The
Khai-Yuan Chan Ching of A.D. 718 stated that earthquakes menaced princes.

Chang Heng also did not confine himself to recording earthquakes. In A.D. 133 a shock affected Lo-yang so severely that the emperor asked for advice and suggestions that might prevent a recurrence. Chang Heng informed him that the palace eunuchs had too much influence, and that the emperor should reassert his authority. Presumably the advice was not followed, as Lo-yang was shaken again in A.D. 138.

The design of Chang Heng's seismograph was passed on for several hundred years. Two scholars of the sixth century A.D. wrote books claiming knowledge of 'the bronze earthquake instrument', but by the thirteenth century these books had been lost, and with them the secret of the seismograph. In about 1290, the writer Chou Mi said that he knew that such a device had once existed, but that he was unable to understand how it could have worked. He wrote, “...this instrument is said to have been placed in the capital far away from where the earthquake occurred. How could...the bronze dragons vomit forth the balls? I cannot at all make out the principle, and would very much like to find someone who understands it.”