This is amazing. As happened with most TV shows of that era, many Doctor Who episodes of the 60's and 70's were "wiped." Many were later found, but there were still quite a few lost, mostly from the show's first decade. There was a common belief that those which were still lost were probably gone for good.

Incredibly, two episodes have been found. One is from an era of the show that is almost totally wiped (Patrick Troughton/Frazer Hines/Anneke WIlls/Michael Craze).

http://www.radiotimes.com/news/2011-12-11/doctor-who-two-long-lost-episodes-uncovered

http://www.bbc.co.uk/doctorwho/dw/news/bulletin_111211_01/Missing_Eisodes_ecovered

This is great news especially since most of the Patrick Troughton era is completely gone, we're lucky that a large part of the Hartnell era still exists.