The only thing I can find is that Jerome had taken a very similar trip along the Thames for his honeymoon in 1888, and his experiences provided him the subject material for the novel. I don't see, in my copy, an acknowledgement to any particular person.
Answer:
Traveling from one place to another.
Impromptu is an unrehearsed speech. Not rehearsing would not allow speakers to gather 100% of their thoughts.