“As against solipsism it is to be said, in the first place, that it is psychologically impossible to believe, and is rejected in fact even by those who mean to accept it. I once received a letter from an eminent logician, Mrs. Christine Ladd-Franklin, saying that she was a solipsist, and was surprised that there were no others. Coming from a logician and a solipsist, her surprise surprised me.” (Russell, p. 180). Russell, Bertrand., Human Knowledge: Its Scope and Limits,London: George Allen & Unwin, 1948.
“Tracking down the Russell joke about solipsism” at petemandik.blogspot.com