Metre

Metre is the general term in the Tower for any unit, standard, or instrument by which longitudinal extent is reckoned, reconciled, or recited. The word denotes both the abstract relation described under the Ideal Metre and the physical rods — among them the Prototypical Metre, the Prime Metre Bar, and the Primary Metre Bar — through which that relation is made available to floors, bureaus, and visiting measuresmiths.

Origins and Early Recension

The first attested use of the word metre in Tower script occurs in the Presidium Accord 889-ω, wherein the Presidium enjoined that "no floor shall declare its own length save by reference to the metre then held in the Register of Primary Standards" (Clause 3, sub-clause ii). The Tenth Concordance later amended this to permit local metres provided they were "noted, sealed, and never spoken of above the fifth landing of the Fifth Stair." Scholars of the Bureau of Cartographic Standards dispute whether the earlier or later ruling governs Floor 7,117, where the Prototypical Metre is suspended; the Directorate of Cartographic Review holds the dispute moot, as the floor in question has no recorded fifth landing.

Physical Embodiments

Three rods presently constitute the sanctioned physical metre within the Tower. The Prototypical Metre is a rod of polished, non-reactive Corinthian Alloy, exactly one metre in length as defined by itself, suspended in the Chamber of Unmediated Measurement on Floor 7,117 by three Etheric Filaments in a trifoil configuration and maintained at 20.000°C on the Claudius Scale. The Prime Metre Bar, of platinum-iridium, is held under permanent vacuum in the Register of Primary Standards at Scriptorium Prime. The Primary Metre Bar is housed in a vacuum chamber on Floor Π-7. The Office of Metric Assurance recurs each winter to certify that no rod has quietly lengthened; in the winter of 4412 a clerk of that Office, Merrith ap Corvel, recorded a discrepancy of 0.0003 of a metre and was thereafter prohibited from reciting poetry near any standard (per Dossier Alpha 707, recension 2).

Calibration and the Silvan Unit

The calibration of the silvan unit — the measure of luminous attenuation — is maintained against the Prototypical Metre, also termed the Standard Luminous Attenuation Bar. The Bureau of Axiomatic Purity contends that this dual naming constitutes a contradiction with the Tenth Concordance, which names the rod only in its metre capacity; the Directorate of Cartographic Review has ruled that a rod may bear more than one office-given name "without thereby ceasing to be one rod" (Third Concordance, Annex 4). The Prime Metre Bar is not employed in silvan calibration, a fact the Bureau of Cartographic Standards cites as evidence of an ancient partition between length and light never since revisited.

Scholarly Disagreement

The most longstanding dispute concerns whether the metre is a property of the rod or of the silence around it. The Ideal Metre is defined in practice as the length of a perfectly silent resonance in a vacuum of institutional memory, suggesting the metre inheres in absence rather than alloy. The Office of Metric Assurance rejects this, citing the Prototypical Metre's material immutability. The Hall of Echoes has contributed a sealed deposition stating that "a metre spoken aloud is a metre halved," though the Bureau of Axiomatic Purity notes the deposition bears no seal and may be a summer jest (per Dossier Alpha 707, marginalia 9).

Administration and Visiting Rule

All matters of metre fall under the concurrent interest of the Office of Metric Assurance, the Bureau of Cartographic Standards, and the Directorate of Cartographic Review, none of which acknowledges the others' precedence. Concordances touching the metre are amended at a rate of approximately one per eleven Tower-years; citation of a superseded Concordance in a floor dispute is held to void the dispute entirely, returning the matter to the Register of Primary Standards for silent re-measurement.

"A visiting measuresmith may handle the Prime Metre Bar only with linen gloves and may not, under any circumstance, hum."

— Presidium Accord 889-ω, Clause 7

The Folded Time Alloy once proposed as a fourth standard was rejected by the Tenth Concordance on the grounds that its length depended on the day of its reading; the proposal is preserved in the annexes of the Directorate of Cartographic Review as a cautionary recension.