How to Emasculate a Persistent Myth
Courtesy of Barry Williams - Editor of The Skeptic (published Australasian Science August 2005)
Royal Navy sailing ships needed to store iron cannonballs near the cannons so they would be ready for instant use, but in a manner that would not let them roll around the gun deck. The answer was to stack them up in a square-based pyramid near the cannon so that four levels would provide a stack of 30 balls. The problem was to prevent the bottom level (16 balls) from sliding out from under the weight of the higher levels. They devised a small brass plate referred to as a "brass monkey", with an indentation for each cannonball in the bottom layer. As temperature falls, brass contracts faster than iron and when it got cold on the gun decks, the indentations in the brass monkey would get smaller than the iron cannonballs. If the temperature became cold enough, the bottom layer of cannonballs 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".
And so, another familiar phrase became part of the language.
It's an amusing yarn, explains a common phrase and is full of detail, but it has one serious problem - it is pure myth. However, it provides an excuse for a skeptic to analyse the elements and sort out the facts from fiction by deduction..
Naval ships did indeed have cannons that fired round iron cannonballs, as did merchant ships. The most numerous ships in the fleets of Nelson's day were designated as "third-rate 74s", which carried 74 guns on three decks. So far so good, but this is about the time when reality departs rapidly from myth.
Cannonballs needed to be stored near the guns ready for instant use.
Sailing ships were completely at the mercy of the wind, so coming into battle often took hours and even days. This was especially so when, as was usually the case, one side was trying to avoid battle. Thus violent engagements were inordinately rare. In fact, the guns were kept loaded at at all times and surplus shot was stored in the hold as ballast. More importantly, the propellant charges were stored in a magazine below the waterline - highly inflammable surplus charges were never stored near the guns, even in a battle. Wooden ships are hard to sink but very easy to burn.
... but in a manner that would not let them roll around the gun deck. The answer was to stack them up in a square pyramid base ... of 30 balls.
The Royal Navy, which was generally much better at gunnery than its opponents, could manage to fire around 30 rounds per gun per hour. In fact, they did keep surplus shot near the guns while in action, but they were either kept in indentations in the wooden hatch coamings or in wooden troughs along the bulkheads between the gun ports.
The problem was to prevent the bottom level (16 balls) from sliding out from under the weight of the higher levels. They devised a small brass plate referred to as a "brass monkey", with an indentation for each cannonball in the bottom layer.
And that might even have worked had their battles been fought on Lake Eyre in mid-summer. Unfortunately for this story, most of the action took place in the Atlantic or Mediterranean in all sorts of weather, with the ship heeling over, pitching, yawing or rolling (and often all at once). When not in use, the guns themselves were lashed to the bulkheads to prevent them from causing damage by running around the deck (hence the term "loose cannon") so the thought of 2220 iron balls (30 for all 74 cannons) being free to roll where gravity took them beggars belief and invites derision.
As temperature falls, brass contracts faster than iron... the indentations in the brass monkey would get smaller than the iron cannonballs... [and] the bottom layer of cannon-balls would pop out of the indentations, spilling the entire pyramid over the deck.
Certainly iron and brass have different coefficients of expansion, but given the tolerances of manufacturing technology at the time and with all the other factors mentioned above, that would be the least of the worries of any captain stupid enough to leave 74 pyramids of 24- or 36-pound cannon balls piled up all over his decks.
The case against this story being true seems incontrovertible, but there is a simpler way to check it. Consult any of the plethora of books and almanacs on naval matters published to commemorate the 200th anniversary of Trafalgar (October 21). In none of them will you find any reference to a "brass monkey". QED