I knew Mahlon Day at Urbana quite well. If he had a mathematician son, I was unaware of it, but you should ask John Gray. Now as far as I know he didn't hire so many category theorists. For example, I was hired by Paul Bateman. So was Jon Beck. As far as I can tell, the only one hired by Mahlon was John Gray. And he may have known Eilenberg, but only as one mathematician may know another. But your entire question is based on a misconception that the hiring at Illinois was based on any sort of plan. The fact is that there was a severe shortage of mathematicians in those days and UI was hiring a couple dozen people a year (and losing a similar number) and anyone who was publishing or well recommended and showed any interest was getting offers. I got at least one utterly unsolicited firm offer from a school I had had no contact with. Possibly, probably, someone like Sammy had given them my name when asked, but that is all. And I received a number of invitations to apply for a job and did and got an offer (and a pay raise from UI). So they didn't even ask what kind of math you did, only that you did some kind of math. Hard to believe what it was like in those days. The people at Illinois who were there for the first midwest category meeting in 1965 were Alex Heller (an algebraic topologist, with an interest in category theory), John Gray (category theorist), Jon Beck (algebraic topology & category theory), Max Kelly (there on a one year leave, category theory), and me (homological algebra). In fact, I wasn't even invited originally; I can thank Max for telling Saunders to invite me. My interest in category theory developed later at the ETH. Now Eckmann is probably the one person most responsible for bringing category theorists together. A history of category theory should talk not only about the founding fathers, but also a certain number of godfathers, people who were not category theorists themselves, but strongly encouraged it. I would include (but not limit it to) Beno Eckmann, Peter Hilton, Alex Heller, David Harrison, .... Of course, there were a number of others who while not primarily category theorists made actual contributions to category theory: Grothendieck, Dan Kan, Albrecht Dold and Dieter Puppe,... Above all, Colin, one should not write a history of category theory without interviewing as many of these people as are still alive and it is damned shame that no one has done this till now. For Eilenberg and Harrison, it is already too late. Michael On Thu, 6 Dec 2001, Colin McLarty wrote:
Working on the history of category theory I find that Mahlon Marsh Day hired several category theorists at the University of Illinois Champaign-Urbana in the 1960s. I would like to know whatever people can tell me about his connections to category theory--perhaps through Eilenberg?
Also, does anyone here know whether Mahlon Michael Day was Mahlon Marsh Day's son? Mahlon Michael Day got a PhD at Chicago in 1967 with Kaplansky.
Thanks, Colin