h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Just t be an anorak,
The term 'to freeze the balls OFF a brass monkey' is not quite explained right. Its not to freeze the balls on, but off the brass monkey. This is caused by the fact that the brass contracts faster than the cannon balls, and actually becomes to small to hlod the stack. thus silors knew it was very cold when the cannon balls decided to go for a little wander on their own!

I've had a go at explaining dogs bollocks before. But have a look at this-
See entry for Bog Standard from the "Box, Standard" car kit. Just the basic no frills.
Now think about the other boxes in the range - the best one would be "Box, Deluxe" meaning everything in, top of the range or the best.

Nobody understood "Box, Standard" and it was soon mispronounced,
"Box, Deluxe" along the same path would be "Bogs Deluxe" which would be seen as a spoonerism to avoid offence(in the same was as nissed as a pewt is used) and would be turned to dogs bollocks by the clever person who doesn't mind, nay, revels in, offending people.

I feel I must ... so I did ... here is a truly illuminating example of science and engineering in an ever expanding (or oscilating) universe (depending on your view-point), to explain this common misconception, in naval terms, a brass monkey was a brass CANNON, (some still exist but not in operational use - although the recent revelation that the Navy is firing blanks and shouting 'BANG !' makes me wonder if they may be 'called-up' pretty soon ...) brass has a greater coefficient of thermal expansion (and, retrospectively (?), of contraction) than cast iron and hence, in cold weather, the brass monkey contracted (ie shrunk) faster than cast iron and so " FROZE THE BALLS IN A BRASS MONKEY"

and now for something completely different, definition of CONTROL is a naval engagement without loss of seamen ... SAY IT, DON'T READ IT

I feel I must agree with previous posts, it is 'freeze the balls off a brass monkey' , the monkey being the storage/delivery system for cannon ball although you are correct re differential expansion rates - for confirmation see www.brassmonkeys.co.uk