To study and encourage popular interest in all branches of Science.

Newsletter August 2007

Dear Member,

I enclose a copy of the Society's lecture programme for the 2007/2008 session.

The first lecture on Adult Brain Stem Cells by Dr Kaylene Young of UCL will take place at 8.15 pm on Thursday 13th September in the Crypt Room at St John's Church, Hampstead.

Council for 2007/8

Membership of Council for this year is:

President - Professor Robert Weale

Secretary - Julie Atkinson

Treasurer - Peter Wallis

Membership Secretary - Elisabeth Fischer

Programme Secretary - Jim Brightwell

Ordinary members - Aileen Cook, Elizabeth Davies, Hemant Desai, Nayna Kumari, John Tennant.

Astronomy Secretary - Doug Daniels

Assistant Astronomy Secretary - Simon Lang

Meteorology Secretary - Philip Eden


Doug Daniels

At the beginning of the last century in 1900, just a year after the H.S.S. was founded, some Greek sponge divers working off the coast of the Greek island Antikythera, discovered the wreck of an ancient ship on the seabed some 42 metres below sea level. Amongst the various items of the ship's cargo to be salvaged were amphorae, pottery, coins, jewellery, glassware, statues and in particular one item that ought to have made a profound impression on the archaeologists of the time; but somehow failed to do so. The object in question was a fragment of what appeared to be some mechanical device. A very corroded circular bronze wheel with two spokes at right angles to one another showed evidence of gear teeth on its perimeter and there were less obvious traces of other geared wheels embedded in the highly petrified and encrusted structure that was still attached to the decomposed fragments of a wooden case. The amphorae and other artefacts from the ship's cargo enabled archaeologists to date the ship's demise to about 85 BC. Moreover, many of the salvaged artefacts appeared to have originated from the island of Rhodes. It is strange that the recovery of any mechanical device that was over 2000 years old did not cause more of a stir in the world of archaeology at the time of its discovery. This is especially so, since mechanical 'clocks' with geared wheels did not come on to the scene in Europe until the fourteenth century. To discover a device with this level of mechanical sophistication and of such great antiquity is absolutely staggering. The more so since recent investigations into the design and structure of this remarkable device have shown it to be a complex astronomical instrument, a computer that could show the positions of the Sun and the Moon relative to the Zodiac, the phases of the Moon, the positions of planets and it could even indicate when eclipses would occur.

Recent investigations of the device using high resolution X-ray tomography have shown it to be far more complex and sophisticated than initially suspected. The mechanism has a train of over 30 toothed gear wheels and the circular dial is covered with many inscriptions of astronomical significance. These inscriptions have only recently been enhanced and deciphered using new scanning techniques. By counting the number of teeth on the gears and referring to the inscriptions, it is possible to understand how the device may have worked. It would appear that the large surviving dial showed the Metonic cycle - 235 months - 19 years, the time taken for the Moon to return to the same phase on the same day of the year. Another dial would have displayed the 223 month Saros cycle used to predict Solar and Lunar eclipses. Yet another dial recorded the 76 year Callippic cycle, an improvement on the Metonic cycle with an error of just one day in 553 years, equivalent to four Metonic cycles minus one day. Although these lunar cycles were well known to earlier Babylonian astronomers, to actually replicate them mechanically in a device of such antiquity is truly amazing. But possibly the greatest discovery was that the device also featured two eccentric gears coupled with a pin sliding in a slot that took account of the apparent irregular motion of the Moon due to its elliptical orbit about the Earth.

This familiarity with the motions of Solar System bodies begs the question: 'Who made it?' The fact that the ship that was carrying it appears to have come from Rhodes may provide a clue. During the first and second centuries BC, Rhodes was the centre of the astronomical research world. From 140 BC until his death in 120 BC, the Greek astronomer Hipparchus worked there and he was succeeded by the philosopher Posidonius.

Hipparchus had already worked out a theory to account for the Moon's irregular orbital motions based on epicycles and it is this feature that is incorporated in the mechanism. A further clue to the device's origins may come from the writings of the Roman lawyer Cicero in the first century BC. Cicero, who spent some time on Rhodes as a student, later wrote a description of an instrument that he had seen and which he attributed to Posidonius. The instrument that he described, accurately depicted the movements of the Sun, Moon and planets about the earth. Could this have actually been the Antikythera Mechanism? We may never know for certain but the very existence of this remarkable instrument engenders enormous respect for its designer and maker, whoever they were. The fact that such a complex astronomical computer was constructed at such an early date raises further questions. Why was this advanced technology not continued and further developed? Why was it on that ship and where was it going? Did its tragic loss effectively hold back technological advance in astronomical instruments for thousands of years? It would appear that the Antikythera Mechanism is a truly unique and anachronistic artefact that provides us a glimpse of a technology that existed briefly in the eastern Mediterranean that went largely unrecorded for two millennia. (For a more detailed description of the origins, workings, and reconstruction of the Antikythera Mechanism read Nature 30 November 2006.)

Our Island

Peter R Wallis

Britain owes much to being an island - its maritime capability, its relative freedom from invasion. But it was not always so. It is known that it was once joined to the continent of Europe if only because during a glacial period, of which there have been many during the last 3 million years[1], the sea level is more than 100 metres lower, leaving the North Sea and English Channel as dry land. But there was once also a more permanent land bridge across the Dover strait, a bridge of chalk rock called the Weald-Artois Anticline. Then the North Sea and the English Channel were separate embayments with separate river systems.

The destruction of this barrier has been a matter of controversy, with little evidence to decide the mechanism. Smith [2], in 1985, proposed that a catastrophic flood eroded it. It is only now that we have clear confirmation from a study by Gupta et al [3] of the morphology of the bottom of the Channel. They use detailed sonar data provided by the UK Hydrographic Office and show that the sea bed rock has been deeply eroded by two massive floods. They are able to make comparison with the Channeled Scabland region of Washington State US caused by the Lake Missoula mega-flood.

A commentary by Gibbard P, another worker in the field, is in the same issue. Gibbard considers that the Weald-Artois anticline was formed ½ million years ago during a major extension of the continental ice-sheet into lowland Europe and Britain and was 30 m above today's sea level. Thus the Scheldt, Rhine, Meuse and Thames rivers would have had no outlet either north or south and built up a vast glacial lake covering the southern part of the North Sea and the low countries. This eventually overtopped the barrier, which was eroded away by the torrential flow. Gupta estimates that the peak flow was about one million cubic metres per second, perhaps the largest seen on Earth. He says that the breach reorganised the palaeodrainages of Britain and north-west Europe by re-routeing the Rhine-Thames river flow through the Channel river during low sea-level glacial periods. It led to separation of Britain from continental Europe during high sea-level interglacial periods, with consequences for early human presence. He also suggests that the massive pulses of freshwater into the eastern Atlantic could have caused episodes of climatic cooling through weakening of the Atlantic overturning circulation as happened more recently with the flooding from Lake Agassiz only 8,000 years ago.


[1] For background information on ice ages see HSS Newsletter for April 2005. Back

[2] Smith A J, "A catastrophic origin for the palaeovalley system of the eastern English Channel", Mar Geol 64, 1985. Back

[3] Gupta S, Collier J S, Palmer-Felgate A & Potter G, "Catastrophic flooding origin of shelf valley systems in the English Channel", Nature, 19th July 2007. Back


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