Strip off the coarse outer leaves, and cut off the stalks close to the bottom. Wash the artichokes well, and let them lie two or three hours in cold water. Put them with their heads downward into a pot of boiling water, keeping them down by a plate floated over them. They must boil steadily from two to three hours; take care to replenish the pot with additional boiling water as it is wanted. When they are tender all through, drain them, and serve them up with melted butter.