The great nineteenth-century mathematician Peter Gustav Lejeune Dirichlet (1805-59) studied in Paris, coming under the influence of scholars including Fourier and Legendre. He then taught at Berlin and G ttingen universities, where he was the successor to Gauss and mentor to Riemann and Dedekind. His achievements include the first satisfactory proof of the convergence of Fourier series under appropriate conditions, and the theorem on primes in arithmetic...