Stonehenge, a Neolithic stone struc-ture that rises majestically out of theSalisbury Plain in England, has fasci-nated man for centuries. It is believedthat Stonehenge was erected overseveral centuries beginning in about2180 B.C.. Its purpose is still amystery, although theories abound. Atthe summer solstice, the rising sunappears behind one of the main stones, giving theillusion that the sun is balancing on the stone. Thishas led to the early theory that Stone-henge was a temple. Another theory,first suggested in the middle of the20thcentury, is that Stonehengecould have been used as an astro-nomical calendar, marking lunar andsolar alignments. And yet a thirdtheory is that Stonehenge was used topredict eclipses. Regardless of why itwas built, there is a mystical quality about the placethat defies explanation.Stonehenge Is Still a Mysteryoperations: addition, subtraction, multiplication, and division. Unfortu-nately, the state of mechanical gears and levers at that time was such thatthe Leibniz machine was not very reliable.
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Ada Lovelace, Charles Babbage, late eighteenth century, sun predict eclipses, Scott Barrett theory