Tuesday, October 28, 2014

Math Words: Obelus

Obelus:  The symbol "÷" which is used to indicate the operation of division is called an obelus.  The word comes from the Greek word obelos, for spit or spike, a pointed stick used for cooking.  Perhaps because both are sharp and used for piercing meat, the word is sometimes used for a type of stabbing knife called a dagger.  The root also gives rise to the word obelisk for a pointed pillar of stone.  The symbol was used as an editing notation in early manuscripts, sometimes only as a line without the two dots, to indicate material which the editor thought might need to be "cut out".  It had also found occasional use as a symbol for subtraction.  It was first used as a division symbol by the Swiss mathematician Johann H Rahn in his Teutsche Algebra in 1659.  By a misunderstanding of a credit to John Pell about other material in the book, many English writers started using the symbol and calling it "Pell's notations".  It is one of the most territorial of all math symbols, appearing in regular use in both the US and Great Britain and yet nearly non-existant in the rest of the world.



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