Floor 491 C

Floor 491 C is a residual designation on Floor 491, applied to the eastern gallery and its four attached reading rooms after the partial collapse of the winter of 4,127. It is not a floor. Concordance 88, Annex 2, is explicit on the point: "A lettered gallery is not a storey, is not numbered, and shall not be counted in any survey of the vertical extent of the Tower." The wording was chosen by Librarian Orst Halversen after an earlier draft had counted Floor 491 C as a separate floor, briefly making the Tower one floor taller in the Register of Extents and provoking an audit that took eleven years to close.

Origin of the designation

The collapse of 4,127 opened the gallery's eastern wall onto a captive void between the old masonry and the Floor 492 foundation course. Rather than rebuild the wall, the Office of Bounded Spaces enclosed the void as usable rooms and the Scriptorium of Provisional Numbers was asked to name the result. Provisional numbers were in short supply that decade — Concordance 61 had frozen the allocation at nine — and the Scriptorium resorted to letters. Floor 491 C opened for readers on 3 Second Frost, 4,129, seventeen days ahead of the reassignment of its copyists.

Floors lettered A through B in the same year were later absorbed back into their parent floors when their voider walls were declared non-load-bearing. Floor 491 C alone survived, principally because the Office of Bounded Spaces discovered that its void contained a small working cistern and has declined to release it.

What is held there

The gallery houses the Errata of Floors 400–500, the Water-Damage Recensions, and a shelf of unclaimed bookmarks. The reading rooms are numbered C-1 to C-4, and C-3 is the only room in the eastern gallery with a window; the window looks onto Floor 492, which has caused three separate complaints to the Bureau of Sightlines. The current inventory is fixed at four rooms, and has remained fixed since 4,131 even though staff have counted five on at least two occasions.

"Where a gallery returns a count in excess of its register, the excess is not an error and shall not be reported. It shall be left in the room where it was found."

— Concordance 88, Annex 4

Use by expeditions

Descending parties bound for the middle floors customarily break at Floor 491 C rather than at the parent floor, on the grounds that the gallery's cistern is closer than the one on Floor 490 and the reading rooms are warmer than the stairhead. The Stairwardens' Guild has never formally authorised this practice. In 4,304 it nonetheless issued a visiting rule, Stairwardens' Guild Notice 22, requiring that no expedition spend more than two nights in the gallery and that boots be left in the corridor. The notice is posted beside the C-2 door and has faded almost to nothing.

Parties returning upward are advised to make their last entry in the gallery log before leaving, as the Errata of Floors 400–500 is not carried to any other floor and has not been for ninety years.

The Halversen objection and the counter-reading

Scholarly opinion divides on whether Floor 491 C qualifies as a holding at all. The School of Fixed Extents maintains that the gallery is a fitment of Floor 491, on the authority of Annex 2 and of the opening sentence of Floor 491's own entry, which makes no mention of it. The School of Administrative Substance, by contrast, cites Concordance 61, Annex 1, which provides that "a place administered shall be treated as a place," and notes that the gallery has been administered, staffed, warmed, and logged as a distinct place for over seven centuries.

The disagreement ripened in 4,812, when a survey party from the Bureau of Vertical Claims counted Floor 491 C in its return and was instructed by the Office of Bounded Spaces to count it again. The corrected return omitted the gallery. The uncorrected return, which had already been sent to Floor 4001, was never recalled, and both figures now stand in the Register of Extents without note.

Maintenance

The void masonry sweats in the spring and requires re-pointing each Second Frost. The north stair to Floor 4,712 does not begin in the gallery and cannot be reached from it; readers who attempt the route are directed down to Floor 490 and across. The cistern is drawn every eighth day by the Water Office, which will not enter C-4 while the fifth room is present.