What weighs more: a pound of gold or a pound of feathers?

Hi everyone! I had intended to write up a full etymology post this month, but time got away from me during the holidays. So for now, I offer an amusing fact taken from Jeff Suzuki’s book, Mathematics in Historical Context

You may know the old joke “What weighs more: a pound of gold, or a pound of feathers?” The answer, of course, is that a pound is the same regardless of what’s being weighed. However, this was not the case in the Medieval world! While the Romans imposed some uniformity of measurement on most of Europe, by Medieval times individual communities had developed their own variations. This bring us to Suzuki:

The complexity of the system of weights and measures is most obvious in what seems to be a nonsensical question: which weighs more, a pound of gold or a pound of feathers? Gold and other precious commodities were measured in Troy units, named after the semiannual trade fairs at Troyes in Champagne, France, where goods from throughout Europe could be exchanged. The Troy pound is divided into twelve troy ounces, and each ounce into twenty pennyweights, and each pennyweight into 24 grains: thus, a Troy pound is equal to 12 x 20 x 24 = 5760 grains. An avoirdupois pound (from the French “having weight”) was defined as having a weight of 7000 grains: thus a pound of gold (5760 grains) weighed less than a pound of feathers (7000 grains). Even more confusingly, the avoirdupois pound was divided into 16 inappropriately named ounces, so an ounce of gold (20 x 24 = 480 grains) was heavier than an ounce of feathers (7000 ÷ 16 = 437.5).

That’s it for now! I will return in the new year with one last post, on the origins of our words for weights and measures.