• Journal for History of Mathematics
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• v.17 no.3
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• pp.33-42
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• 2004

${\varrho}$ is the real constant number that appears not only in calculus but also in a real life. The concept of the number ${\varrho}$ first appeared in an appendix of Napier's work on logarithms in 1618. The early developments on the logarithm became part of an understanding of the number ${\varrho}$. In 1727, the number ${\varrho}$ was studied by Euler explicitly. It ton14 almost 100 years to understand the number ${\varrho}$ which we learn in high school nowadays. By studying the origin of the number ${\varrho}$, we can guess that many mathemetician's research in our time will have significant meaning in the future although it looks like just some calculations of cohomology or K-theory etc.