Sigma-Secundus (Silent hemisphere)

Sigma-Secundus is the lower hemisphere of the Halved Bell of Aperture Sigma, a cast-bronze resonance body recovered in two unequal parts from the Aperture Sigma-7 stairwell. It is the hemisphere of the pair to which the Silent Interval is principally attributed. Where Sigma-Prime rings a clear C-sharp when struck, Sigma-Secundus returns no tone at all: any object used to strike it is rendered acoustically and kinetically inert for 4.7 seconds, and during that period the object cannot be made to sound, swing, fall, or be struck a second time. The effect is local to the instrument and the immediate air about it, extending in practice to a radius of roughly two paces and, on one contested reading of Order Secundus, somewhat further.

The hemisphere measures 61 centimetres across the rim, carries a casting seam of the Aperture Sigma foundry, and is stored in a felt-lined cradle on the Sigma landing, mouth downward. It is not to be inverted. Visitors are asked to leave hats with the landing clerk, as the bell's cavity has on three occasions been mistaken for a receptacle.

Description and behaviour

Sigma-Secundus is unornamented on its outer face but bears, just inside the rim, a band of fourteen short incisions whose spacing has never been satisfactorily explained. The inner surface is dulled where the striking point falls, consistent with sustained use. The approved instrument for striking either hemisphere is Tool Σ-7B-1, and no other tool is to be applied; the Bell Ledger records each strike by date, hemisphere, hand used, and the name of the tester.

The inertness produced by Sigma-Secundus is total for its duration. Testers have reported that a dropped striker neither accelerates nor arrests but simply occupies its position, and that a struck tuning fork gives up its hum at once and resumes it — unchanged in pitch, though not in count — at the 4.7-second mark. The interval is measured from the moment of contact and not, as is sometimes assumed, from the moment the sound would have been expected to begin.

Custody and testing

Strikes are conducted under the standing guidance of Order Secundus, which fixes the posture of the tester, the direction of the strike, and the manner of withdrawing the tool. The order's current instrument of guidance is a recension of the eleventh winter, prepared after the incident of the compounded strike, in which two testers applied Tool Sigma-7B-1 in the same motion and neither tool was thereafter available for 4.7 seconds to the person holding it. A holder of Voss-Secundus may sit as a non-voting assessor at any panel convened to review such an event, though the assessor is not to be seated within the two-pace radius.

Comparisons with the Aperture 12-Sigma Resonance are frequent in the custodial literature and are, on the whole, unhelpful; the two bodies resemble one another in profile only, and the resonance has never been induced to fall silent.

Disputed readings

The principal scholarly disagreement concerns what, precisely, is made inert. The reading long dominant in the Silent Stacks holds that the effect attaches to the object that strikes the bronze — the tool, and the tool alone. A minority position, defended at length in the Sigma-4 commentary and adopted in the annexes to Material Filing Sigma-9, holds instead that the effect attaches to the whole field of contact, such that a hand holding the tool is also, for 4.7 seconds, unable to close. The distinction is not academic: the Sigma Regulator has twice declined to certify testers on the minority reading, on the ground that it cannot be verified without a tester who is willing to be unable to let go.

"The instrument is silenced; the hand is not. Let the record show that the hand was never in question, and let no further motions be entered upon the point."

— Order Secundus, Annex 6, marginal ruling of the custodian on duty

A third view, advanced by the clerk Jurist Sigma-1 in a note appended to the 17 Sigma 8819 inventory, proposes that nothing is made inert at all and that the interval is simply the time the bell requires to decide. This has not been refuted. It has, however, been filed.

Recorded incidents

In the winter of the year the Dock Sigma manifests were re-sealed, a tester at the Sigma landing struck Sigma-Secundus with a borrowed key rather than the approved tool. The key was inert for 4.7 seconds; the tester, unwilling to wait, attempted to pull it free, and the resulting strain was entered in the Ledger under a heading the clerk invented for the occasion. The heading has since been regularised. Keys are no longer lent at the landing.

The most-cited incident remains the disputed strike of the ninth recension, when a tester recorded a strike on Sigma-Prime that three witnesses placed on Sigma-Secundus. The Bell Ledger has been amended twice in consequence and now requires the hemisphere to be named aloud before the tool is raised. The two entries remain in the volume, uncancelled, one above the other, in different hands.

Status

Sigma-Secundus is held in perpetuity as a custodial object and is not available for loan, demonstration, or comparative study. Its silence is regarded within the Tower as settled fact; its cause is not, and the Silent Stacks continue to receive deposits on the question at a steady if unhurried rate. No expedition has been authorised to determine whether the hemisphere would fall silent outside the Tower, and it is not proposed to ask.