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Every sailing ship had to have cannon for
protection. Cannons of the times
required round iron cannonballs. The master
wanted to store the cannonballs
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 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 because the cannonballs
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 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."
This from Jim Hampton.
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