In days of old when warships sported cannons, the cannonballs were stored on brass railings called monkeys.  These monkeys held the cannonballs securely.  That is until cold weather set in, for cannonballs were made of iron and in cold weather iron would contract more than brass allowing the cannonballs to slip through the railings, resulting in the cannonballs rolling around on deck.  This necessitated the sailors to store the cannonballs in pyramids on the deck, securing the bottom of the piles with rope.  Thus, the old naval saying, “it’s cold enough to freeze the balls off a brass monkey.”  That is how cold it is today!