Haertel, and real, like Einstein (see image), Dirac, Mach, Milne and Dingle (see here). A "Mach drive" is one of Poul Anderson's several FTL drives. Rereading HG Wells' The Time Machine (London, 1973), we find and take for granted this topical reference:
"'...some philosophical people have been asking why three dimensions particularly - why not another direction at right angles to the other three? - and have even tried to construct a Four-Dimensional geometry. Professor Simon Newcomb was expounding this to the New York Mathematical Society only a month or so ago.'" (Chapter 1, p. 9)
We accept Newcomb as we accept every other period reference in The Time Machine. The text is rich in such references, placing this novel firmly in its own period before its protagonist launches himself "'...into futurity.'" (Chapter 4, p. 25) Now, however, it is an easy matter to google the pre-Einstein Newcomb, who even turns out to have written a science fiction novel!
Anderson and Blish cite Einstein etc when rationalizing their FTL drives. Now Newcomb, expounding four dimensional space, joins this august company. It is quite a thing to be named in The Time Machine.