Like others said, writing; actually, not much has changed since then, other than that the letters are written much faster and delivered / replied to instantly. Read biographies or stories about the pre-internet scientists (Einstein, Hawking, andsoforth), and you'll find a lot of references to letters written. In fact, the biographies are often based on those.
There's a lot more letters written nowadays (electronically), and a lot of those are short-lived and easily forgotten. Exceptions are those posted on news groups or meticulously archived. Everything someone has ever written on the internet is a veritable treasure trove of people's opinions and lives and whatnot, probably even moreso than personal diaries from back in the day. Also a lot more static.
There's a lot more letters written nowadays (electronically), and a lot of those are short-lived and easily forgotten. Exceptions are those posted on news groups or meticulously archived. Everything someone has ever written on the internet is a veritable treasure trove of people's opinions and lives and whatnot, probably even moreso than personal diaries from back in the day. Also a lot more static.