Smiling and maybe a little too quick to wave, Jim Mason is no tough, stone-faced security guard. Standing post at the entrance to the (still relatively) new Central Library downtown, Mason, 65, says he keeps his voice to a whisper when he tells people they are breaking the rules. Before his library gig, Mason spent 30 years guarding galleries at the Nelson-Atkins Museum of Art before retiring in July 2001. The last ten of those years, he worked the graveyard shift, keeping himself occupied by gazing at the walls and singing. It was a lonely job. Maybe that's why he's so damned friendly to the people in the library. When confronting a visitor who is talking too loudly, walking in drunk to use the restroom or downloading porn on the computers, Mason pulls out his library rule book and politely asks the patron to stop. "He's my top employee right now," says Ronell Bailey, safety supervisor for security at the library.