A pound of lead feels heavier than a pound of feathers - a thing long suspected, but not carefully tested until recently, when Jeffrey B Wagman, Corinne Zimmerman and Christopher Sorric ran an experiment involving lead, feathers, plastic bags, cardboard boxes, a chair, blackened goggles, and 23 volunteers from the city of Normal, Illinois.

The scientists are based at Illinois State University, which is located in that unassumingly named metropolis. In a study published in the journal Perception, they explain why they took the trouble: "'Which weighs more - a pound of lead or a pound of feathers?' The seemingly naive answer to this familiar riddle is the pound of lead, whereas the correct answer is that they weigh the same. [The] naive answer may not be so naive after all. For over 100 years, psychologists have known that two objects of equal mass can feel unequally heavy depending on the mass distribution of those objects."

Wagman, Zimmerman and Sorric poured some lead shot into a plastic bag, then sealed and taped the bag inside the bottom of a cardboard box. For clarity, let's call this the box-with-lead-in-its-bottom. Then they stuffed a pound of goose down feathers into a large plastic bag. This fluffed, baggy entity entirely filled a box that looked just like the box-with-lead-in-its- bottom. Let's call this snugly-packed second box the box-with-feathers-spread-thoughout-its-innards.

Then came the test. One by one the volunteers sat in the chair, donned the blackened goggles, then "placed the palm of their preferred hand up with their fingers relaxed. On a given trial, each box was placed on the participant's palm in succession. The participant hefted each box and reported which felt heavier."

Slightly more often than not, the volunteers said that the box-with-lead-in-its-bottom was heavier than the box-with-feathers-spread-thoughout-its-innards.

After weighing and judging all the data, the scientists educatedly hazarded a guess as to why one box seemed heavier. Probably, they said, it's because "the mass of the feathers was distributed more or less symmetrically in the box (ie, the feathers filled the box), but the mass of the lead was distributed asymmetrically along the vertical axis (ie, the box was 'bottom-heavy'). Therefore the box containing lead was more difficult to control, and it felt heavier."

The scientists did not test how volunteers would respond if the lead were precisely in the middle, rather than stuck to the bottom, of the box. This they left for future scientists to contemplate.

(Thanks to Chris McManus for bringing this to my attention. Professor McManus won the 2002 Ig Nobel medicine prize for his excruciatingly balanced and adequately illustrated report Scrotal Asymmetry in Man and in Ancient Sculpture, which was published in the journal Nature.)

· Marc Abrahams is editor of the bimonthly Annals of Improbable Research and organiser of the Ig Nobel prize