A History of Mathematical Notations, Volume II

Florian Cajori's A History of Mathematical Notations is the standard historical reference on the origin and spread of mathematical symbols, compiled by a mathematician who spent decades tracing individual notations back through primary printed sources. Its authority is that of a meticulous documentary survey rather than a single argued thesis, and its treatment of the infinity symbol is representative of its method, establishing John Wallis's 1655 introduction of the symbol as documented fact while treating proposed explanations for why Wallis chose that particular shape as conjecture rather than settled history. Its age is a real limit, since some individual attributions have been refined by later scholarship working from sources Cajori did not have access to, so a specific claim is worth confirming against a newer specialist study, but its core documentary record of who used which symbol and when remains the reference most historians of mathematics still consult first.