Readers of the Mathematical Intelligencer may be interested to know that the notation π was introduced 314 years ago, in 1706, or approximately 100 π years ago, by the Welsh mathematician William Jones. As Florian Cajori wrote in [4]:

It was in that year that William Jones made himself noted, without being aware that he was doing anything noteworthy, through his designation of the ratio of the length of the circle to its diameter by the letter π. He took this step without ostentation. No lengthy introduction prepares the reader for the bringing upon the stage of mathematical history this distinguished visitor from the field of Greek letters. It simply came, unheralded, in [a] prosaic statement.

Jörg Arndt and Christoph Haenel [1] refer to Jones as a self-made mathematician. It was in his Synopsis palmariorum matheseos (A New Introduction to Mathematics) [6], based on his teaching notes, that Jones introduced his notation. For more information, the interested reader can consult the paper by Patricia Rothman [8], or the books by Petr Beckman [2], David Blanter [3], Jean-Paul Delahaye [5], Alfred Pasamentier and Ingmar Lehmann [7], and Alexander Zhukov [9].

In addition to the “π-centenary” of the notation, many readers surely know that there are two celebrations each year, Pi Day on March 14 by the Americans and Pi Approximation Day on July 7 for Europeans. The former because Americans refer to that date as 3.14. The latter due to the Archimedean approximation of π as the ratio 22/7.

This recalls a quip attributed to George Bernard Shaw (which may well be apocryphal): “The United States and Great Britain are two countries separated by a common language.” He did not mean the language of mathematics, though. Those who want to be politically correct can surely celebrate both dates.