At noon on Monday, October 24th, 1887, Dr. Edmund G. Husserl defended the dissertation that would qualify him as a university lecturer at Halle. Entitled "On the Concept of Number," it was written under Carl Stumpf who, like Husserl, had been a student of Franz Brentano. In this, his first published philosophical work, Husserl sought to secure the foundations of mathematics by deriving its most fundamental concepts from psychical acts.¹