Sounds of the Adriatic
QUESTION At Zadar in Croatia, is there a musical organ played by the power of the sea?
THE Sea Organ, opened in 2005, is a popular tourist attraction in Zadar.
In 1944, this beautiful and ancient Adriatic town, then under Italian rule, was heavily bombed by the Allies and the harbour was destroyed. After the war, the mangled concrete and iron was replaced by a monotonous wall.
As part of a Millennium project to reshape the town’s shoreline, architect Nikola Basic submitted plans to harness the sounds of the sea. The Sea Organ uses the power of the waves to force air through a
series of underwater pipes embedded in a wide marble stairway that lines the water’s edge.
Heaving seawater enters the immersed tubes and works like a piston to push air through a resonant chamber beneath the promenade. The musical tones created exit through openings in the top of the stairs.
There are 35 polyethylene pipes in sets of five spread across seven segments of stone steps. The sets of pipes are tuned to one of two major chords that span the masculine vocal range, similar to that found in traditional Dalmatian songs. The sounds produced rely on the wave energy’s random time and space distribution.
Basic also created the promenade’s other attraction, the Sun Salutation. This is a 72 ft-diameter solar disc formed from 300 multilayered glass panels. Under the disc are a series of solar panels that power 10,000 LED lights. Each lamp changes intensity and colour based on computer input correlated with the sounds of the Sea Organ, producing a co-ordinated light and sound show.
T. R. Lewin, Lyme Regis, Dorset.
QUESTION What caused the greening of the Sahara desert thousands of years ago?
THE greening of the Sahara is known as the African Humid Period when this area was covered in lush vegetation. It was caused by changes in Earth’s orbit around the Sun. While the processes that initiated the process began 15,500 years ago, it is usually dated between 11,500 and 5,000 years ago, as it was interrupted by a drying event known as the Younger Dryas.
At this time, much of the Sahara was covered by grasses, trees, rivers and lakes. These conditions were reflected in paradise myths such as the Garden of Eden in The Bible and Elysium and the Golden Age in classical antiquity. Saharan rock paintings depict pastoral scenes with elephants, giraffe, hippos, aurochs (a wild ancestor of domestic cattle) and antelope.
Earth’s axial rotation is affected by gravitational interactions with the Moon and the larger planets. This induces periodic changes in the orbit around the Sun, known as Milankovitch cycles.
These are a 100,000-year cycle in the shape of Earth’s orbit (eccentricity), a 41,000-year cycle in the tilt of its axis (obliquity) and a 20,000-year wobble of the axis (precession). It is this that caused the African Humid Period as it
resulted in Earth passing closer to the Sun. This increased the solar radiation absorbed by the North African landmass by up to 8%.
This ensured the Sun was blazing down on the Sahara with full intensity. The land cooked and increased convective air currents. As warm air rose, wet air was drawn in from the Atlantic to replace it.
The process was analogous to the one that created the monsoon in Asia. Rains were recycled by rich vegetation across North Africa. The continually moistened winds took precipitation to the heart of the Sahara.
The process came to an abrupt halt. In less than 100 years, the Saharan rivers emptied, swamps dried up, bush died and rain clouds were replaced by sandstorms, creating one of the harshest environments on Earth.
For 3,000 years, the precession of Earth became increasingly unfavourable, the warm air rose a little less and the monsoon did not penetrate as far inland. Eventually the process stopped.
A host of other environmental factors, such as glacial expansion in the Himalayas, the expansion of sea ice in Antarctica and changes in sea currents, may have accelerated the end of the North African monsoon.
Dr Ian Smith, Cambridge.
QUESTION Was there a glider that could fly tanks on to the battlefield?
DURING World War II, the Allies made extensive use of gliders to land airborne troops. Britain made an even bigger glider, the General Aircraft Hamilcar, that could carry large loads including 17-pounder anti-tank guns and vehicles. The Hamilcar could also carry two types of light tank, the American M-22 Locust and the British Tetrarch.
However, these had limited effectiveness as they had thin armour and a puny gun.
Hamilcars were used to transport tanks on D-Day and the Rhine crossing.
Historians have speculated that the outcome of Operation Market Garden (Arnhem) might have been different if Hamilcars had taken Tetrarch tanks to Holland.
A squadron of Jeeps equipped with Vickers K machine guns was supposed to capture the Arnhem bridge within an hour of the initial landing, but they were ambushed by German soldiers armed with machine guns.
If Tetrarch tanks had been available, they could have captured the bridge ahead of airborne forces arriving and prevented the Germans from sending forces south across Arnhem to reinforce Nijmegen.
The Germans also had a large transport glider, the Me 321, that theoretically could transport light tanks, but it was considered to be a failure.
Dr Colin M. Barron, Dunblane, Stirling.
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