A NAUTICAL LESSON
Anonymous 

I have
always had an interest in the day to day phrases we Americans use but have no
idea of their origination. Perhaps this will explain this one. - Jim
Muse
Every sailing ship had
to have cannon for protection. Cannon of the times required round iron
cannon balls. The master wanted to store the cannon balls such that they
could be of instant use when needed, yet not roll around the gun deck.
The solution was to stack them up 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 cannon balls. 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 cannon ball in the bottom
layer. Brass was used because the cannon balls wouldn't rust to the
"brass monkey", but would rust to an iron one. When
temperature falls, brass contracts in size faster than iron. As it got
cold on the gun decks, the indentations in the brass money would get smaller
than the iron cannon balls 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 money."
Not being a nautical
type, I have to take their word for this one. If it is not true, then
someone went to great lengths to make up a story. Rebuttals anyone?
Incidentially, I have also sent this to some people are Coast Guard related.
Maybe I can get a reading from them.