did you know?
 

In the heyday of sailing ships, all war ships and
many freighters
carried iron cannons. Those cannon fired round iron
cannon balls. It
was necessary to keep a good supply near the cannon.
But 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
thirty 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 out from under the others. The
solution was a
metal plate called a "Monkey" with sixteen round
indentations.
But, if this plate was 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
cannon balls would come right off the monkey. Thus,
it was quite
literally, "Cold enough to freeze the balls off a
brass monkey!"