Apogeic

The term apogeic designates, in Tower usage, any measurement, structure, or condition taken at the highest certified interior elevation of a given enclosed volume. It is at once a unit, a qualification, and a jurisdictional claim, and the confusion among these three senses accounts for a substantial fraction of the archive's contested holdings. A space is not apogeic merely because it is high; it is apogeic because a certified surveyor has said so, in writing, on a form that has not since been superseded.

Definition and certification

Apogeic height is defined under Third Concordance, Annex 9, as the vertical distance from a floor's datum to the highest point of its enclosed ceiling, measured along a plumb line held by two persons and witnessed by a third. The definition presumes enclosure: open shafts, stairwells, and the exposed faces of The Stones carry no apogeic figure, and surveys attempted upon them are returned unstamped. The distinction matters because the Department of Structural Verifications will not accept an apogeic figure from an unenclosed surface even where the geometry is unambiguous, and has twice declined to do so in writing for reasons it describes as "the maintenance of category."

Certification is ordinarily the work of the Guild of Theoretical Mechanics, whose surveyors carry the apogeic plumb in a fitted case of seven weights. The Guild certified the apogeic height of Verity's Span in Cycle 12,401, returning a figure of 4.2 meters, which remains the largest recorded apogeic grotto ceiling in the archive. That figure has been challenged only once, and unsuccessfully.

The apogeic survey and its instruments

The instruments of survey are few and their replacement is slow. The plumb is a braided cord of specified twist; the weights are numbered; the witnessed form is duplicated in triplicate, one copy of which is retained by the Guild, one filed with the Department of Structural Verifications, and one sealed and not opened. The sealed copy is the operative one. This arrangement was introduced during the Schism of the Calibrated Span (Cycle 13, Pericline 22 to Cycle 15, Apogeic 7), when the definition of absence and the boundaries of guild jurisdiction were disputed at length and the sealed copy emerged as the only record neither party could amend unilaterally.

Surveys are conducted at low traffic hours. A survey in progress is marked by a cord across the approach and a placard bearing the surveyor's number. Members of the Guild of Theoretical Mechanics are not obliged to answer questions during a survey, and the placard is not obliged to explain them.

Apogeic use in husbandry

The most consequential application of apogeic certification lies not in architecture but in animal husbandry. Vellum for Verity Ink documents must be prepared from the hide of a calf born within the apogeic grotto of Verity's Span — that is, within the certified enclosure, below the certified ceiling, and not in the surrounding pastures however elevated. The requirement is jurisdictional rather than physiological; no study has established that a calf born at apogeic elevation is distinguishable from one born a meter below it, and the Salt Flats Curatorial Authority has said as much in a footnote.

The certified sound-dampening pastures adjoining Verity's Span are, by contrast, explicitly not apogeic, a point the Authority has had occasion to state three times. Silent Calf husbandry depends on the dampening, not the elevation, and the two qualifiers have never been granted together.

Disputes and contradictions

Two Concordances address the question of whether an apogeic figure survives alteration of the space it describes. Third Concordance holds that certification attaches to the plumb line and lapses when the line is moved. The Codicil of Petrified Voices holds that certification attaches to the ceiling and survives any alteration short of its removal. The readings are irreconcilable, and the Department of Structural Verifications has adopted the practice of filing both and deciding neither.

A second dispute concerns spaces whose ceilings fall below the surveyor's reach without scaffolding. The Guild maintains that scaffolding is not a structural element and does not alter the apogeic figure; the Authority maintains that a ceiling reached only by scaffolding was never enclosed in the relevant sense. The Salt Flats of Floor 44 have been surveyed both ways, with results differing by 0.31 meters, and both figures remain in circulation. That the Salt Flats of FloorFoor 44 carry a separate and unrelated certification is a filing error of long standing and should not be read as a third figure.

Related elevations and false cognates

Apogeic is not to be confused with tidal, which describes periodic vertical movement and is treated under Tidal Librations. Nor is it to be confused with the merely high: Floor 4,200 is high, and its height is not apogeic, because the floor above it has never been certified as a ceiling. Floor 44 is neither high nor low and has no apogeic figure at all.

Where an apogeic enclosure contains standing brine, the apogeic figure is taken to the ceiling and not to the waterline, a rule affirmed at Pulmonary Brine Pools after a surveyor's error in Cycle 12,914. The error was corrected within the same survey season and the correction filed in the sealed copy, which is the only reason anyone now knows about it.

"An apogeic figure is a statement about a ceiling made by a person standing on a floor. It is not a statement about height in general, which is nobody's business."

— Third Concordance, Annex 9, marginal note

Where a certified apogeic space is later found to contain no ceiling at all, the certification is void from the date of survey and the surveyor's number is retired. This has happened twice. The Codicil of Petrified Voices records both retirements and, in the same entry, disputes the reasoning behind them, which is characteristic of the document.