Preheat oven to 350°. Mix together the peaches, sugar, cinnamon and lemon juice. Allow the mixture to sit while you make the batter, so the juices can be drawn out of the peaches. Put the butter in a 9 x 13-inch glass baking dish and place the dish in the oven while it's preheating. As the butter is melting, mix the batter by combining the flour, baking powder, salt, sugar and milk. When the butter is completely melted, remove the pan and pour the batter into the melted butter. Then carefully spoon the peach mixture evenly over the batter. Return the dish to the oven and bake for 45 minutes. As the cobbler cooks, the batter will begin to rise up and around the peaches.