Sunday, May 17, 2009

Transit of Hardship

In the 18th-century, scientists were trying to measure the passage of Venus across the Sun. If correctly measured from multiple places on Earth, one could then work out the distance to the Sun and other planets. However, these "transits of Venus" only happen "in pairs eight years apart, but then are absent for a century or more." So when the first of a pair of such transits came around in 1761, scientists from all over the world set off to take measurements.

Many suffered disasters of various kinds, but among the unluckiest of these observers was a Frenchman named Guillaume Le Gentil:

Le Gentil set off from France a year ahead of time to observe the transit from India, but various setbacks left him still at sea on the day of the transit -- just about the worst place to be since steady measurements were impossible on a pitching ship.

Undaunted, Le Gentil continued on to India to await the next ransit in 1769. With eight years to prepare, he erected a first-rate viewing station, tested and retested his instruments, and had everything in a state of perfect readiness. On the morning of the second transit, June 4, 1769, he awoke to a fine day, but, just as Venus began to pass, a cloud slid in front of the Sun and remained there for almost exactly the duration of the transit: three hours, fourteen minutes, and seven seconds.

Stoically, Le Gentil packed up his instruments and set off for the nearest port, but en route he contracted dysentery and was laid up for nearly a year. Still weakened, he finally made it onto a ship. It was nearly wrecked in a hurricane off the African coast. When at last he reached home, eleven and a half years after setting off, and having achieved nothing, he discovered that his relatives had had him declared dead in his absence and had enthusiastically plundered his estate.
--from pp. 54-55 of Bill Bryson's A Short History of Nearly Everything.

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