Harmonic Void Sigma (Floor Ω-201)

Harmonic Void Sigma

Harmonic Void Sigma is the formal designation of the principal Harmonic Void maintained on Floor Ω-201, in the middle register of the western spiral. It is the largest continuously instrumented Void open to unsupervised measurement in the Tower, and for this reason it is used as the working reference against which the Office of Harmonic Integrity calibrates field apparatus that cannot be brought to the sealed Primary Resonant Standard. Its fundamental frequency is recorded at 43.6 Hz, a figure stable to within 0.2 Hz since continuous observation began in the winter of the year 44 of the present recension.

The Void is circular in plan, 11.4 metres across, and sunk 2.3 metres below the floor plate. It has no bottom that has been established. Sound introduced at the rim returns at the same pitch but measurably later, and the delay does not correspond to any depth so far proposed.

Designation and status

The name is a source of persistent confusion. Harmonic Void Sigma is not a Sigma Pulse and is not connected to any Aperture. It takes the letter from the survey sheet on which it was first plotted, in the hand of the surveyor Orra Vane, whose habit was to letter voids in the order she reached them rather than by any systematic scheme. By the time the Guild of Harmonic Theorists regularised void nomenclature, the letter had appeared on four hundred and six floor plans and could not be recalled.

Under the Third Concordance, section 14.8.ii, the Void is classified as a primary resonant feature and is therefore subject to the Laws of Harmonic Containment in full. It is additionally held under Standing Notation Ω-201/7, which permits visitors to descend to the second gallery but not to the floor plate. The prohibition is not a safety measure. Clerks who reach the plate disturb the delay readings for eleven days.

Measurement history

Early records from Floor Ω-201 are fragmentary. The Void appears in a floor inventory of the year 9 as "the ringing place, unlet," and in a requisition of the year 12 for 40 metres of rope and one lamp. Between those dates the floor is described in the accounts as occupied, though no occupant is named and no rent is recorded.

Systematic measurement dates from the appointment of the clerk Halvard Senn to the floor in the year 41. Senn established the 43.6 Hz figure by the then-standard method of matching a struck tuning fork against the Void's returned tone, and he kept a daily ledger for nineteen years. His entries are unusually terse. The entry for the third of the eleventh month of the year 52 reads in full: "Same. The fork agrees. I do not."

Senn's ledger was later seized during the Harmonic Integrity Review of the year 63 and entered in the Review's schedule of irregular instruments. It has not been returned. The floor's readings after the year 63 were taken by rotation until the permanent post was restored in the year 71.

The delay dispute

The return delay at Harmonic Void Sigma is the subject of a disagreement between two offices that has now outlasted every clerk party to it. The Office of Harmonic Integrity holds, on the authority of its own handbook, that the delay is a property of the Void's fabric and is therefore constant. The Clerks of the Balanced Void, who are licensed to enter and stabilise, hold that the delay varies with the helical pattern of Void-Chalk laid at the rim, and that a Void measured without fresh chalk is not measured at all.

"A void that has not been chalked has not been heard. It has only been listened to."

— Clerks of the Balanced Void, instruction to entrants, clause 3

The dispute is procedural rather than physical, since neither office disputes the other's figures once the chalk state is recorded. It persists because the record-keeping has never been reconciled. The Harmonists' returns for Floor Ω-201 carry a column for chalk condition; the Clerks' returns do not carry a column for the Harmonists' column. A joint schedule was proposed in the year 88 and printed in an edition of ninety copies, of which eleven were distributed before the print run was found to have transposed the two offices' seals.

The Claudius Scale is used at the Void for cross-referencing diffraction readings taken with the Umbra Scale Ruler. Readings are taken at the second gallery only.

Relation to other voids

Harmonic Void Sigma is frequently compared to Harmonic Void Alpha on Floor Ξ-447, whose 47.3 Hz fundamental is the older and better-known figure. The comparison is invited by the Guild's accreted conceptual potential theory, which predicts that voids of similar diameter should accrete at similar frequencies. Sigma's 43.6 Hz is 3.7 Hz below Alpha's, a divergence the Guild attributes to the age of the surrounding shelving and the Office of Harmonic Integrity attributes to nothing, having declined to comment in writing since the year 74.

The Void is not to be confused with the Void Annex, which lies on the same floor but is administered separately, nor with Aperture Sigma-12 in the upper spireworks of Spiral 44, with which it shares only a letter and a persistent mis-filing. Requests for the Sigma file are misdirected between the two roughly once a month. The Grand Harmonic Repository on Floor Ξ-719 holds the consolidated record.

Incidents

In the winter of the year 59 a visiting scholar of the Guild attempted to lower a weighted line into the Void to establish its depth. The line was recovered after four hours, unweighted, and 1.1 metres shorter than it had been paid out. The scholar's report describes the loss without speculation and concludes only that the line "should not be counted against the floor's allowance." No further depth attempts have been licensed.

The floor's most cited incident remains the misdirection of the year 84, when a delivery of chalk consigned to the Clerks was entered against the Void's maintenance account and the Clerks' stabilization rite for the third quarter was consequently performed with a substitute compound. The delay readings for that quarter are excluded from all averages. The floor's standing notice, painted at the head of the second gallery stair, dates from the following year and reads: Chalk is signed for at the stair. Not below it.