I also have a guest entry done on chickpea981 if you'd like to wnder over there too :)

Since it is getting cold here again, I thought I would share with you the following DYK from last year.

How cold is it here today? Well... In days of old, Cannonballs would be stacked in pyramids. Because they were round, they would roll away unless they were placed on something to help lock them into position.
This 'something' was called a Mount-key and was made of Brass.

Cannonballs were made of Iron.
Anyone who has every studied physics and done experiments in school with a Bimetal strip will know that Brass and Iron expand and contract at different rates.
So when it got really cold, these mountkeys would contract, and "Sproinngg!!" the Cannonballs would pop off.
It was therefore possible to judge how cold it was by whether or not it was cold enough to freeze the Cannonballs off of the Brass Mountkey.
Over time, this passed into the vernacular as the expression
'Cold enough to Freeze the Balls off a Brass Monkey'
So now you know...