The Second Book of General Ignorance Read Online Free PDF

are caused not only by the gravitational effect of the moon but also by atmospheric pressure, depth, salinity, temperature and the shape of the coastline.
    The relatively big tides in the Gulf of Gabes result from its shape. It is a wide, shallow basin, about 100 kilometres (60 miles) wide by 100 kilometres long. The gulf acts as a funnel,the tidal energy forcing water into a progressively smaller space, thereby increasing the rise in sea level – and, correspondingly, lowering it on the way out. The same thing happens on a much greater scale in the Bristol Channel, which has a tidal range of over 9 metres (30 feet).
    Tidal effects are at their strongest when the sun and moon are on the same side of the earth (new moon), or on the opposite side (full moon), and their gravitational pulls combine to create the strong ‘spring’ tides (‘spring’ in the sense of ‘powerful forward movement’, not the season).
    The Phoenicians founded Gabes in about 800 bc. Pliny the Elder first noted its unusually large tides in AD 77 in his Natural History . He also recorded that Gabes was second only to Tyre in the production of the expensive purple dye made from murex shells, which the Phoenicians discovered (hence the Greek for purple, phoinikeos ), and which was highly prized by the Romans: the toga purpurea was worn only by kings, generals in triumph and emperors.
    The Mediterranean is bigger than you might think. At 2,500 square kilometres (965 square miles) it covers the same area as Sudan, the largest country in Africa, and would comfortably swallow Western Europe (France, Spain, Germany, Italy, Greece, Britain, the Netherlands, Belgium, Switzerland and Austria combined). Its coastline stretches for 46,000 kilometres (28,000 miles) or about twice the length of the coastline of Africa. Nor is it particularly shallow: its average depth is over 1½ kilometres (about a mile) while the North Sea’s is a mere 94 metres (310 feet) and, at its deepest point, in the Ionian Sea, it reaches down nearly 5 kilometres (over 3 miles), substantially deeper than the average depth of the Atlantic.
    Six million years ago, the Mediterranean dried out completely in the so-called Messinian Salinity Crisis. This created the largest salt basin that ever existed and raised the sea level of the rest of the world by 10 metres (33 feet). Threehundred thousand years later, the rock barrier at the Straits of Gibraltar gave way – in a cataclysm called the Zanclean Flood – producing the world’s largest-ever waterfall and refilling the whole of the Mediterranean in as little as two years. The tide would have risen 10 metres every day. But it wouldn’t have gone out again.
    STEPHEN The Mediterranean was once the biggest dry lake in the world. In the late Miocene era.
    ALAN The water came rushing in over the Strait of Gibraltar.
    STEPHEN You’re quite right. Six million years ago.
    ALAN I know this because I saw it in the Plymouth Aquarium.
    JIMMY CARR That must have been fabulous for all the towns around Spain and Portugal that rely on tourism. When that came in, they went: ‘This is fantastic. Finally these jet-skis are going to get an outing.’

Which birds inspired Darwin’s theory of evolution?

    Many smart people would answer ‘finches’, but actually it was mockingbirds.
    The great passion of the young Charles Darwin (1809–82) was killing wildlife. As a student at Cambridge, when the shooting season started, his hands shook so much with excitement he could hardly load his gun. Though studying medicine and divinity to please his father, he dismissed lectures as ‘cold, breakfastless hours, listening to discourses on the properties of rhubarb’.

    But he was also an enthusiastic amateur biologist and fossil-hunter and was keen to see the tropics, so he signed on as a ‘gentleman naturalist’ for HMS Beagle ’s second survey expedition (1831–6). He almost didn’t get the job: the captain was keen on physiognomy and thought that