Aperture Cycles

Aperture Cycles are the measured intervals governing the opening, closure, phase-shift, and periodic re-attestation of the apertures catalogued within the Tower. The term is used in three distinct senses, which the Bureau of Civil Cycles has twice declined to reconcile: the cycle of practice (the interval over which an aperture is observed and maintained), the cycle of appointment (the residential and administrative term within which an Aperture Registrar serves), and the cycle of designation (the interval after which an aperture's reality status must be renewed, presently fixed at fifty). Disputes over which sense a document intends are the single largest category of unresolved citation before the Concordance clerks.

Origin and the First Aperture

The system of Aperture Cycles is held to have originated with the First Aperture, which is said to have established the practice of counting intervals rather than measuring openings. According to the recension preserved on Floor 7114, the First Aperture opened and closed without record for an indeterminate period until a junior cataloguer began marking each closure with a chalk tally on the surrounding masonry. The tally was thereafter kept, and the keeping of it became the cycle.

The treatise on Aperture Cycles assembled in the ninth scriptorium fixes the early period at intervals "not shorter than the time required to walk the tally-stair twice, nor longer than the patience of the keeper" (On the Maintenance of Inter-Floor Apertures, Book II). Later commentators have observed that this is not a measurement. It has nonetheless been cited in preference to every measurement proposed since.

Discovery in the Third Cataloguing Cycle

The formal discovery of Aperture Cycles is credited to the Third Cataloguing Cycle, during which cataloguers working the non-linear stacks found that certain phenomena could not be described except by describing when they recurred. The finding redefined the cataloguing of non-linear phenomena generally: a phenomenon that cannot be dated is now entered by cycle alone, with its duration left blank and a marginal note directing the reader to the relevant Registrar.

The reform was not accepted everywhere at once. The keepers of the western stair refused cycle-based entries for eleven years, on the ground that a thing without duration is a thing without extent, and a thing without extent cannot be shelved. Their objection was eventually withdrawn after a fire in the western stacks destroyed only those holdings that had been given durations, a coincidence the keepers recorded without comment.

Appointment and the Registrars

Specific residential and administrative cycles determine when Aperture Registrars are appointed, how long they serve, and which floors fall within their warrant. The cycles are not aligned, and a Registrar appointed within one may find their residential cycle expiring while their administrative cycle has two-thirds still to run. This is considered normal. The Bureau of Civil Cycles has ruled that a Registrar whose residential cycle has closed remains competent to record and validate formal dating arrangements until such time as they are formally relieved, and that being formally relieved is not, in itself, a residential matter.

"The Registrar shall not be removed from office by reason only of having gone home."

— Concordance 71, Annex 6, clause 4

A well-attested consequence is the case of Registrar Onde Vessit, appointed to the twelfth landing in the winter of Cycle 402, whose residential cycle closed in 407 and whose administrative cycle was not adjudged complete until 419. Vessit continued to validate dating arrangements for twelve years from a chair carried down from the residence, and the arrangements so validated were upheld in every subsequent review. The Ledger of Dwindling Cycles records the episode without remark.

Renewal, lapse, and the Kappa-Class problem

The reality status of a designated aperture must be renewed every fifty Aperture Cycles. Renewal is performed at a Kappa-class aperture, an aperture reserved for the measurement of Kappa Cycles and for attesting to the presentness of conditionally substantial items. Where renewal is not performed, the aperture is not closed but is reclassified as pending, a status under which it may be described but not relied upon.

Pending apertures are the subject of a standing disagreement between the Bureau and the Aperture Regulatory Office. The Bureau maintains that a pending aperture has no cycle, since a cycle requires something to recur. The Office maintains that a pending aperture has precisely one cycle — the fifty-cycle interval of its lapse — and that this is the only cycle it has ever had. The disagreement has been carried through four recensions of the Regulatory Annexes without resolution. Annex 9, which fixes the phase alternation of Aperture 317-1 at twenty-seven hours, is silent on the matter and has been read in support of both positions.

Irregular cycles and sealings

Not every aperture keeps a clean cycle. Aperture 12-β was temporarily sealed between Cycles 845 and 847 following the Kappa-Aperture Discrepancy, during which its renewals were recorded twice for the same interval; the duplicate was not detected until after the second renewal had been attested. Apertures sealed under such conditions do not accrue cycles during the sealing, but their next renewal falls due as though they had. Aperture 7 Gamma has been sealed three times and is now considered to owe cycles it has not yet lived.

Irregularity of this kind is distinguished from the ordinary irregularity of apertures such as the Wardrobe Aperture, whose cycle is not periodic and has never been claimed to be. The Wardrobe Aperture opens; the Tower records that it opened; no cycle is assigned. This is permitted, though the Bureau has noted its discomfort.

Record-keeping and custody

Cycle entries are held in the Central Pneumatic Stacks, whose dispatch cycles are regulated by the Central Chronometer and whose maintenance cycles are frequently not. Entries are kept in duplicate, and the duplicates are kept apart. Where an aperture falls out of use, its cycles pass with its papers into the custody of the archive and are subject to Clause 2; where an inquiry concerning a cycle remains unanswered after 899 standard Tower cycles, it is transferred to permanent archival custody under Codicil 127, which is the usual fate of the difficult ones.

The condition of the record is uneven. Cataloguing of Temporal Stability requires a benchmark of not fewer than three cycles, and much of the older material was entered at two. Readers consulting cycle entries on the lower floors are advised that a discrepancy of a single cycle is customary and should not be reported. Discrepancies of two or more should be reported to the Registrar, who will not be able to resolve them.