What do Sir Henry and Dr. Watson discover about Barrymore and his candle?

Sir Arthur Conan Doyle's The Hound of the Baskervilles is one of his many stories following the adventures of the famous fictional detective Sherlock Holmes. In the novel, Mr. Barrymore is the butler at Baskerville Hall.
Holmes sends Dr. John Watson along with Sir Henry to do some observing at Baskerville Hall and to send him regular reports of what is going on. Watson immediately sees Mr. Barrymore as a possibly suspicious character. One night, Watson is woken up by the sound of Barrymore's footsteps moving across the hall. He gets up and sees Barrymore carry a candle to a window, signaling to someone out on the moors.
Mrs. Barrymore confesses to Watson and Sir Henry that her husband has been using the candle to communicate with her younger brother, Selden, the escaped convicted murderer living on the moors. The Barrymores have been leaving out food for him so that he will not starve, and they use candles to signal when food has been placed.