That Funky Monkey
Interesting tale related by the Father-in-Law:
In the age of wind power and naval empire, cannons emplaced in ships were the ultimate weapon. The problem was the ammunition fired by those cannons, better known as cannonballs, which tended to roll all over the place on a ship. Of course, sailing ships were crewed by men who were wise, clever, and learned* and posessed of rather a lot of free time. These men invented a tray made specifically for holding cannonballs. The trays were basically squares of metal with indentations to hold cannonballs; they provided stable bases for pyramids of balls. Early on, it was discovered that the trays could not be made of iron (or steel) because then the iron (or steel) cannonballs would rust onto the tray and become useless (or at least not readily available). So brass was used.
Now, it's a little known fact that brass and iron (or steel) contract at different rates when exposed to low temperatures. This fact was demonstrated repeatedly when ships posessing brass trays full of cannonballs sailed into cold climes, causing the trays to contract and the balls to fall off, which created a mess and, worse, a ruckus.
Somewhere along the line, some clever sailor decided that "cannonball tray" was too prosaic and boring. He coined the term "monkey" to describe these copper and zinc storage devices.
And the next time the temperature dropped, he (or one of his comrades) noted that it was
"cold enough to freeze the balls off a brass monkey".
Here endeth the lesson.
*just ask Gilbert and Sullivan