Brass monkey

It was necessary to keep a good supply of cannonballs near the cannon
on war ships. But how to prevent them from rolling about the deck was
the problem. The best storage method devised was to stack them as a
square based pyramid, with one ball on top, resting on four, resting on
nine, which rested on sixteen. Thus, a supply of 30 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/rolling from
under the others. The solution was a metal plate with 16 round
indentations, called a Monkey. 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. And all this time, you thought
that was a vulgar __expression, didn't you?