The letter e may now no longer be used to denote anything other than this positive universal constant [the solution of the equation ln x = 1]—EDMUND LANDAU, Differential and Integral Calculus (1934)
Some Additional Remarks on Napier’s Logarithms
In his Mirifici logarithmorum canonis constructio, published posthumously in 1619, Napier explained his invention of logarithms in terms of a geometric-mechanical model, a common approach to solving mathematical problems at the time (we recall that Newton used a similar model in describing his idea of fluxions). Consider a line segment AB and an infinite ray parallel to AB and extending from C to the right (fig. 76).