Fourth Spiral Reservoir

Scope

The Fourth Spiral Reservoir is the annex and custodial vault charged with housing, calibrating, and periodically re-certifying the Standard Mole of the Fourth Spiral, the reference measure against which all quantities drawn from or deposited into reservoir works of the Fourth Spiral sector are adjudicated. It occupies the whole of Floor 4,004-C, a landing of irregular plan measuring 31 metres by 27.4 metres at its widest, and is bounded above by the mid-spiral chandlery and below by the Lower Spiral drop-shaft. The annex is also, secondarily, and by an arrangement the Librarians describe as incidental rather than foundational, the storage point for the bitumen supply used to seal the chambers of the Gallery of Un Light. Traffic between the two functions is considerable, and the corridor serving them was re-laid three times in the winter of Year 47 of the current cycle alone.

The Standard Mole

The Standard Mole of the Fourth Spiral is a solid silver cylinder of 127.3 millimetres in length and 40.2 millimetres in diameter, standing on a three-legged plinth of black basalt. Its mass is fixed by reference to a master casting held in the Reservoir's own strongbox, and the pair are compared by the Office of Measures twice per annum, on the second Tuesday of the flood months and the second Tuesday of the draw months. Calibration disputes are older than the current plinth. The most durable, and least resolved, concerns whether the Standard Mole governs volume at rest or volume in transit — a question that has produced two contradictory readings in the Sixth Concordance's own annexes and remains unsettled. Sennel's argument, recorded in the marginalia of the Office of Measures as Sennel's Turn, holds that no measure can be standard if it must be moved to be compared; the Office of Measures holds that it must be moved, since nothing is legible in the dark of the strongbox. Both positions have been cited in support of opposite rulings on the same day.

Bitumen supply

The bitumen kept here is drawn from seep-lines maintained along the lower wall of the annex, collected in clay vessels of the type still fired for the Inkwell Atrium trade. It is dark, faintly warm to the touch, and slow to set in cold weather — a property the sealers of the Gallery of Un Light regard as a defect in all other grades. The supply arrangement dates from an ordinance of Year 22 of the Fourth Spiral, which directed that a single point of issue be maintained for both measure certification and sealant draw. The consolidation was intended to reduce the staff required; in practice it produced the present arrangement in which a clerk certifying a mole increment may be asked, mid-affixing, to initial a bitumen requisition for an unrelated floor.

"No measure shall be certified while the vessel under test is in contact with any substance issued from the same counter, save by written leave of the Office of Measures."

— Fourth Concordance, Annex Δ, Clause 7

Leave has been granted on four occasions since the clause was entered, most recently during the shortages of the winter of Year 47.

The corridor question

By far the longest dispute on record concerns the corridor serving the annex, which the Office of Measures counts as 41.6 metres and the Office of Circulation counts as 44.0 metres. The discrepancy is unexplained. Two separate committees have walked the corridor with cords; each returned a figure matching its own commissioning office. The matter was referred to the Cabal of the Fourth Aperture, whose stairwell jurisdiction the corridor intersects at one end, and thence — after a period of no recorded activity — to the Whispering Atlas Petition, which sought to re-survey the whole sector. Until the survey is complete, the corridor is signposted at both ends with its own length, each sign citing the opposing office. Visitors are asked not to adjust either sign.

Staffing and access

The annex is attended by two keepers and one apprentice, a complement the Circulationist pilot program briefly proposed to convert to a single rotating post. The proposal lapsed after the first rotating keeper, having drawn a mole increment at the close of one shift, found no counterpart on the following shift willing to receive it. The increment remains, by the terms of the Office of Measures' own register, in transit. Access is granted by countersignature. The strongbox itself is opened twice per annum and at no other time without a Concordance citation; the bitumen counter opens each morning at the eighth bell and closes when the clay vessels are empty or the keeper's handlamp fails, whichever occurs first.