Aristophanes, in the Clouds, says that Socrates and Chærephon tried to measure how many times its own length a flea jumped. They took in wax the size of a flea's foot; then, on the principle of ex pede Herculem, calculated the length of its body. Having found this, and measured the distance of the flea's jump from the hand of Socrates to Chærephon, the knotty problem was resolved by simple multiplication.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
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