What's a Convict?

It was Christmas Eve, and I had to stir the pudding for the next day with a copper stick from 7 to 8 by the Dutch clock. When I had done my stirring, I was taking a final warm in the chimney corner before being sent up to bed. There was a convict off last night, said Joe aloud, after sunset gone, and they fired warning of him. And now it appears they're firing warning of another. Who's firing, said I? Drat that boy interposed my sister, frowning at me over her work. What a questioner he is. Ask no questions, and you'll be told no lies."