Brass Monkey

 

In the  heyday of sailing ships, all war ships and many freighters carried iron cannons. Those cannons fired round iron cannon  balls. It was necessary to keep a good  supply near the cannon. However, how to prevent them from rolling about the deck? The best storage method devised  was a square-based pyramid with one ball on  top, resting on four resting on nine, which rested on sixteen. Thus, a supply of 30 cannon balls could be  stacked in a small area right next to the  cannon. There was only one problem...how to prevent the bottom layer from sliding or rolling from under the others. The solution was a metal plate  called a "Monkey" with 16 round indentations. However, if this plate were made of iron, the iron balls  would quickly rust to it. The solution to  the rusting problem was to make "Brass Monkeys." Few landlubbers realize that brass contracts much more and  much faster than iron when chilled.  Consequently, when the temperature dropped too far, the brass indentations would shrink so much that the iron  cannonballs would come right off the  monkey. Thus, it was quite literally, "Cold enough to freeze the balls off a brass monkey."