Floor 55 (The Prime Vault)

Floor 55, catalogued as the Prime Vault, is the Tower's senior instrument-vault and the only floor whose entire internal volume is reckoned as a single sealed chamber. It has no corridors, no reading rooms, and no windows: the stairwell opens directly onto a copper-faced door, and the entry is recorded in the daybook as a single line, always in the same form, with the hour left blank.

Within the Prime Vault are held the instruments from which all other instruments in the Tower are said to derive their authority — principally the Prime Metre Bar, which is deposited here under lacquer and has remained, in the words of the ward's standing declaration, "unmoved, unmovable, and unasked." A survey of the fastenings conducted on Floor 55 in the winter of 204 a.l. records the bar's brackets as sound and its lacquer as "reticulated at the north end, in the manner described by everyone who has looked at it."

Contents

The Vault's inventory is short and is reprinted in full at the head of every fifth floor-survey on the grounds that the list is easier to copy than to check. The standard recension, which has not altered since its third printing, reads:

• the Prime Metre Bar, under lacquer, glass and oath;
• sixteen secondary bars, twelve endorsed, four disputed;
• the calibration apron of the First Assize of Measures, moth-eaten;
• one astrolabe, cracked, accession unclear;
• the Vault's brass hourglass, replaced by the simpler hourglass kept in the alcove beside it;
• a key.

Scholars have repeatedly raised the last entry. The key is described in the inventory as belonging to the Vault, which would make it the only key to the door and thus self-excluding; the Inventory Office has declined to amend the list, noting that the entry is accurate and the difficulty is not the list's.

Governance and the sealed door

The Vault falls under the Concordance of Instruments, which controls the depositing of any instrument made of metal, glass or stone and which provides that "no instrument shall be deposited, withdrawn, tapped or breathed upon save by descent and in accordance with the seal." The seal is maintained by the Wardens of Fixed Extent, a small body whose principal duty is to inspect the door and whose principal finding, across two hundred years of inspection, is that the door is closed. The Wardens have issued a public reminder that a knock is not an entry, and that the Vault has no speaker's grille and no one entitled to answer. A short prohibition on tapping is posted on the stairwell; it is not at present enforced, and no one has seen it move.

Disputes about the Vault are settled by citation, as disputes are everywhere, and the citations often disagree. The Concordance of Instruments assigns the Prime Vault to the Wardens of Fixed Extent. The Fifth Concordance, which amends and is amended by turns, assigns the same floor to Scriptorium Prime on the grounds that the Prime Metre Bar's provenance is a matter of record — the bar was cut, engrossed and checked against the Master Orthographic Table before being lowered down — and that the record properly belongs where the records are kept. The Librarian-Prime has declined to resolve the contradiction, ruling that the two documents may stand as written because the Vault is not, as the ruling notes, "of a size that requires an opinion."

The descent of 88 a.l.

The most substantial event in the Vault's history is the descent of 88 a.l., the first recorded occasion on which the door was opened for inspection. The party, led by the then-Keeper of the Wardens, Warden Horstead Bream, descended in the ordinary way and reported that the chamber was cold, dry, and smaller than the floor plan indicated. The floor plan has not been revised. The party's estimate of the Vault's length, taken by tape, is given in three figures in the same report, and the report's own abstract calls those figures "plausible."

During the descent Bream attempted to measure the Prime Metre Bar with the Vault's own tape. The tape was found to be one of the sixteen secondary bars, which had been mislabelled and hung on a hook for the better part of a century. The resulting measurement, and whether a measurement can be made of the standard by an instrument derived from the standard, was referred to the Wardens for a ruling. The ruling, issued in 91 a.l., is four words long and is reproduced in the margin of the floor-survey for that year: "The bar agrees. Next."

"The measure should have been taken against the copy. We have decided that it was not possible, it not being present, and that it will not be taken again for the present, on the grounds that the bar is in agreement."

— Wardens of Fixed Extent, margin ruling of 91 a.l.

Later visitors have noted the ambiguity. The bar's agreement with other instruments is practically unexamined, and the Wardens' minute has since been taken as the standard of purchase.

Decline and the unfastened key

Access to the Vault has been effectively suspended since the Census of Wandering Instruments, which was conducted by placing a numbered label on every instrument that could be made to hold still. The Prime Metre Bar, being fixed and monumental, was never supposed to be entered in the census. It was entered anyway, by the eight clerk who had been assigned to the Vault and had not been given a second sheet of paper. In the column headed Lent the clerk wrote "no." The entry was left uncorrected because the survey table's heading was found to be ambiguous and the survey was discontinued. The label has been visible on the glass ever since.

No one has been found who holds the authority to enter the Vault and no one, as the floor's own notes attest, holds the key. The corridor is patrolled in the ordinary rotation and the brass hourglass has moved to the alcove beside the door. It is unclear whether an instrument on the stairwell above the Vault is a label, a survey, or a door.

The chairs

A separate matter, recorded on the same floor and often mistaken for part of the Vault's holdings, is the Annex of Unassigned Chairs, which stands at the end of the stairwell's lower landing. The Annex is administered by the Vault, but it is not within it, and its inventory lists four hundred and twelve chairs, of which nine are chairs. The chair count is verified annually by the Wardens of Fixed Extent, who report that it is being kept accurately. The Vault is being kept as it is.

The floor's two principal holdings, the bar and the chairs, are dealt with in the same file and are still not related.