Physics in The Book of the New Sun

a series of novels by Gene Wolfe

An Introduction
to the novels
The Urth
and its Sun
The Sword
Terminus Est
The Ship
which sails between the stars
Means of Excruciation
and other miscellany
and bibliography

Terminus Est...

After permitting a client to kill herself in order to escape further torment (a most dishonorable act for a member of the Guild of Seekers for Truth and Penitence), Severian is banished from the citadel and dispatched to an outlying province. Upon his disgraceful departure, he is given a gift of an executioner's sword - Terminus Est.

"He was lifting something so dark it was swallowed by the shadows. I said, "Let me assist you, Master."

"No need, no need. Light to raise, weighty to descend. Such is the mark of a good one."

At first it is unclear what is meant when the sword is described as light to raise and weighty to descend. The following page offers clarification.

I clasped Terminus Est as I had the false sword at my elevation, and lifted her above my head, taking care not to strike the ceiling. She shifted as though I wrestled a serpent.

"You have no difficulty?"

"No, Master. But she writhed when I poised her."

"There is a channel in the spine of her blade, and in it runs a river of hydrargyrum - a metal heavier than iron, though it flows like water. Thus, the balance is shifted towards the hands when the blade is hight, but to the tip when it falls..."

Hydrargyrum is another word for the element Mercury, which we can assume is either identical ot similarly massive to the substance that runs through the channel of the sword. If we imagine a sword prepared for an executioner laying on a table, to be raised by the executioner to a near-vertical position above his or her head, the executioner must apply both a translational and a rotational force to the sword. The translational force will be dependent on the mass of the sword, but the rotational force necessary will depend on both the mass of the sword, and the distance of the sword's center of mass from the executioner. With a much of the mass in liquid form able to shift through the sword, after tilting up the blade just a small amount, the center of mass will shift in the direction of the hilt, lessening the amount of torque needed to raise the sword. Once the sword is raised, it is ready to be brought down upon some poor soul's neck. The executioner will move the blade swiftly to increase the force of impact, accelerating its rotation and downward motion. If the executioner rotates the blade swiftly enough, centripetal acceleration will force the massive liquid to the tip of the blade, increasing the blades moment of inertia, and the force with which the end impacts the doomed person's spine. This is what makes Terminus Est an effective blade for the purposes of ceremonial executions.