My big Balls

I can almost hear Bob Wills and "Big Balls in Cowtown" playing in the background.

On British ships of war the brass monkey was a cast frame to hold a pyramid of cannon balls in place on the deck. The differential in shrinkage between brass and iron would occasionally combine with rough seas to produce great confusion on the deck, and became a frequent reference point in conversations about the weather.

Most sailing ships had a cannon for protection. Cannon of the times required round iron cannonballs. Ready use cannonballs were stacked in a square-based pyramid next to the cannon. The top level of the stack had one ball, the next level down had four, the next had nine, the next had sixteen, and so on. Four levels would provide a stack of 30 cannonballs.

The only real problem was how to keep the bottom level from sliding out from under the weight of the higher levels. To do this, they devised a small brass plate ("brass monkey") with one rounded indentation for each cannonball in the bottom layer. Brass was used so the cannonballs wouldn't rust to the brass monkey.

Due the difference in metal composition and mass, the brass contracted in size faster than the iron. As it got cold on the gun decks, the indentations in the brass monkey would get smaller than the iron cannonballs they were holding. If the temperature got cold enough, the bottom layer would pop out of the indentations spilling the entire pyramid over the deck. Thus it was, quite literally, "cold enough to freeze the balls off a brass monkey."