Reading Jonathan Swift’s “The Drapier’s First Letter (to the shop keepers, tradesmen, farmers, and common people of Ireland, concerning the brass half-pence coined by Mr. Woods),” I came across an apparent discrepancy or confusion.
Written in 1724, Swift’s anonymous letter objects to the English imposition of this debased currency, noting that Mr. Wood had procured a patent to coin £108,000 in copper half-pence pieces. The Wikipedia article on Mr. Wood notes that the patent licensed him to coin this sum from 360 tons of copper at 30 pence to the pound (lb.). In the Eighteenth Century, the metal value of coins was not much less than the nominal value of the coins themselves. A Swift put it:
the halfpence and farthings in England pass for very little more than they are worth. And if you should beat them to pieces, and sell them to the brazier you would not lose above a penny in a shilling.
But Mr. Wood made his halfpence of such base metal, and so much smaller than the English ones, that the brazier would not give you above a penny of good money for a shilling of his;
So I tried to do the math. 360 tons x 2000 lbs per ton x 30 pence per pound (lb.) = 21,600,000 pence. Since there were 240 pence to the pound sterling (£), this seemed to be only £90,000. I double checked all my sums. Confirmed that 12 pence to the shilling x 20 shillings to the £ = 240 pence per £. (For an American like me, the use of pounds avoidupois (lbs.) to weigh the copper versus the pound sterling (£) was an added confusion. But it was clear that the “30 pence to the pound” referred to the number of coins to be obtained from one pound (lb.) of copper, i.e. sixteen ounces or 454 grams, if you like.)
Then it hit me, English tons, or “long ton,” per Wikipedia article on the ton, noted that there were 2240 pounds to the long ton, used in pre-metric U.K. and other Commonwealth countries, other than the U.S. and Canada. I dimly recalled the notion of s different “ton,” and the number “2240” also seemed familiar. I re-did the arithmetic, 360 x 2240 x 30 / 240. That equalled 100,800. “Oh, somewhere the 8 got moved around.” Nope. Double-checked the articles and my math. There was no transposition anywhere. WTF?
I even consulted this 1903 book on the Coinage of William Wood, by Philip Nelson. It confirmed everything described above, but shed no light on the discrepanacy.
How did he get £108,000 from 360 tons of copper, at 30 pence per pound? It did not add up.
Finally, with more Googling and reference to the O.E.D., I discovered that iron, and presumably other metals like copper, were measured with a “longweight” ton, equal to 2400 pounds (lbs.). And yes …
360 x 2400 x 30 / 240 = £108,000.
As an aside, Nelson book points out that Woods’ coinage was only about 25% debased, compared to English coins circulating at the same period. Swift’s claim that the coins were grossly debased was a great exaggeration. Nonetheless, in politics and public opinion, the appearance can be greater than the reality. Not unlike the Stamp Acts and Tea Act in the American colonies, Wood’s coinage was perceived as another example of high-handed English exploitation. While there were many, many instances of exploitation in England’s 700 year domination of Ireland, this was (in fact) one of the least.