and when you're talking about specific scriptures in the bible, quote them, or show them to him straight from the bible. don't just say, "the bible said the earth was a sphere", show/tell him what scripture its in. Then tell him how old that passage is. Then show him what encyclopedias said was the prevailing thought at the time that scripture was written. Remember, the Bible is the most powerful object you possess, and the most distinguishing trait of Jehovah's Witnesses, is our use of the scriptures.