Flying Eggs

Scientists are gullible and easy to fool

Joseph Needham, in Science and Civilisation in China, Vol 4, Part 2, page 596, said:

"Easter merry-makers in +17th century Europe had an entertaining trick of making empty eggshells rise in the air literally 'under their own steam'. This is reported in many books, for example Jacques de Fontenay's poem L'Oeuf de Pasques of +1616, which describes it as a traditional custom. The procedure was simple enough, requiring only a little deftness; the contents of an egg being emptied through a small hole and the shell very carefully dried, the right amount of dew (pure water) was introduced and the hole closed with wax. Then in the hot sun the egg would move uneasily, grow light, and rise up into the air, floating a moment before falling."

In a footnote, Needham explains that the hot steam inside the egg is just sufficiently buoyant to raise the shell for a short time into the air before being dissipated [by leaking through pores in the shell and the hole when the wax melts]. Then he goes on, as usual, to show that it was all done in China a lot earlier, and gave rise to the Montgolfiers' balloons and the Kaiser's Zeppelins.

Well, a normal large hen's egg has a volume of about 70 ml, and the shell weighs about 7 grams. An unboiled egg is sealed by a material in the shell, and by a membrane that excludes water but through which gases can diffuse for the respiration of the embryo. A boiled egg cannot be emptied through a small hole, and the dried membrane of an unboiled egg would probably be a good seal. That is neither here nor there, however, since the weight of the air displaced by the eggshell is about 0.09 grams, and this is the maximum buoyant force. Filled with water vapour, the buoyancy is closer to 0.035 grams, which is too small for liftoff by a factor of 200. If I have not made some gross error, I believe it would be a waste of time trying to fly eggs.

These flying eggs are food for thought when evaluating the credibility of modern authors. We should not be too hard on Aristotle and Pliny when they report similar tales, since they had something of an excuse.

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Composed by J. B. Calvert
Created 23 February 2000
Last revised 23 February 2000