Full Idea
The nature of infinity and continuity belonged in former days to philosophy, but belongs now to mathematics.
Gist of Idea
Infinity and continuity used to be philosophy, but are now mathematics
Source
Bertrand Russell (Introduction to Mathematical Philosophy [1919], Pref)
Book Reference
Russell,Bertrand: 'Introduction to Mathematical Philosophy' [George Allen and Unwin 1975], p.-6
A Reaction
It is hard to disagree, since mathematicians since Cantor have revealed so much about infinite numbers (through set theory), but I think it remains an open question whether philosophers have anything distinctive to contribute.