Stones from the heavens

Ambrogio Sodani, a professor of geology and zoology at the University of Siena at the time, studied the phenomenon and found that the stones fell in an area of 47 square kilometres. He estimated their number to be a few hundred. Their sizes ranged from a small pebble to a 3.5-kilogram rock. He tested them with a magnet and concluded that they were mostly iron. They appeared similar to other stones from the sky that he had seen before.

The famous biologist Lazzaro Spallanzani, who was in Naples in 1788 while Mount Vesuvius was in eruption, suggested that a tornado had carried the Siena stones from Vesuvius, 320 kilometres away, which had again erupted just eighteen hours earlier. But Sodani believed that the stones he had collected were different from the volcanic stones of Mount Vesuvius. He suggested that they had come from the sky. Everyone ignored his suggestion except Ernst Florens Friedrich Chladni, a physicist from Wittenberg in Germany (he was a corresponding member of the Academy of Sciences at St Petersburg, and rightly Russia also claims him).

Just two months before the stones fell in Siena, Chladni had published a slim book, On the Origin of Iron-masses, in Riga. In this book, he claimed that stones and masses of iron fall from the sky and some of them even create fireballs in the atmosphere. He suggested that these objects originated in 'cosmic space' and might be remnants of planet formation or planetary debris from explosions or collisions.

Chladni's idea that meteorites were extra-terrestrial in origin was scientific heresy: it was an attack on the great Newton himself, who believed that apart from the heavenly bodies - stars, planets and comets - all space beyond the moon was empty (the heavens are empty of all matter except a very thin, invisible ether, he said in 1704).

Chladni's book was ridiculed by the scientists of his time. 'By all means you must read Chladni's infamous book on iron masses', Alexander von Humboldt wrote to a friend. Georg C. Lichtenberg 'wished Chladni had not written his book'. He felt that Chladni had been 'hit on the head with one of his stones'.

The idea that rocks don't just fall out of the sky was so entrenched that even America's scientifically literate president, Thomas Jefferson, is believed to have commented, 'Gentlemen, I would rather believe that two Yankee professors would lie than believe that stones fall from heaven', when told that two Yale University professors had reported the fall of meteorites over Weston, Connecticut, in December 1807.

We do not know whether Jefferson's remark is truth or myth, but we do know for sure that the French Academy of Science was one of the staunchest critics of Chladni and continued to reject his ideas, even though stones were literally falling in front of bewildered witnesses (at Wold Cottage, England, on 13 December 1795; Evora, Portugal, on 19 February 1796; and Benares, India, on 19 December 1798). When a spectacular shower of several thousand stones fell near the town of L'Aigle in northern France on 26 April 1803, which was witnessed by many French officials, the Academy hastily dispatched one of its members, physicist Jean Baptiste Biot, to investigate the phenomenon. 'I collected and compared the accounts of the inhabitants: at least I found some of the stones themselves on the spot, and they exhibited to me physical characters which admit of no doubt of the reality of their fall', Biot wrote in his report. The report finally convinced the scientific establishment that stones do fall from the heavens.

Astronomers now remember Chladni as the founder of meteoritics, the science of meteorites; physicists remember him as the founder of acoustics for his mathematical investigation of sound waves (the patterns formed when a thin plate, covered with sand, is made to vibrate are still called Chladni figures).

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