Cantor wrote a landmark study in the history of mathematics. Gauss, Dirichlet, Weber and Steiner all taught him. In Paris, he met Bertrand, and Chasles, who encouraged Cantor’s historical work. Cantor (who was only very distantly related to Georg Cantor) said that Gauss always seemed to have an excuse not to deliver his lectures; Gauss was at the end of his career, and Cantor probably his last doctoral student. Cajori was one of those who Cantor, himself aging, gathered around him to help produce the fourth and final volume of his magnus opus.