Aetheric Furnace

The Aetheric Furnace is a generic designation applied by the Tower's plant registers to any heat-raising structure whose working volume is charged by aetheric rather than combustible means. The term is taxonomic, not specific, and its use is a frequent source of confusion: no fewer than nine hundred and forty installations currently answer to it, of which the great majority are small, unstaffed, and of interest only to the offices that meter them. Its most celebrated instance — and the one that has largely absorbed the name in common speech — is the Furnace of Quiet Oblivion, which abuts the western face of the Aetheric Furnace proper and shares with it a common flue wall.

Regulation of the class falls to the Bureau of Latent Significance, which since the winter of 631 has been reviewing the biogeochemical pathways of aetheric transduction in connection with the Furnace's standing operating envelope. The review remains open.

Classification and the Register of Heats

The Fifth Concordance establishes four grades of aetheric furnace, distinguished by draw rather than size. A Grade I furnace raises a working temperature sufficient to soften Sigma-Glass Precursor for binding; a Grade II furnace anneals metals; Grade III serves the light-and-warmth trades; Grade IV is defined only negatively, as any aetheric furnace not falling into the first three, and is therefore where nearly everything ends up.

Grade IV registration is not a formality. Each installation requires a Class-3 Oneiric Artefact to be lodged with the local register as a stabiliser, and installations that cannot produce one are sealed rather than licensed. The Dream Registry holds the greater part of these lodgements, which is why its reading galleries sit, by long arrangement, above the Tower's densest concentration of Grade IV heats.

Construction

The chamber of a first-order aetheric furnace is built of Sigma-Glass Precursor bound in annealed steel. The bands are supplied from the ovens of Floor 909, which has held the band contract without interruption since the recension of the Ninth Concordance; the chamberboys of that floor refer to the work simply as "hooping," and regard the furnaces themselves as remote and slightly pretentious customers.

Aetheric draw is taken from the floor's ambient matrix rather than from any fuel. This has the practical consequence that a furnace performs best when the surrounding floor is busy and worst when it is empty, a dependency the Bureau's review was convened to explain and has so far only measured.

The Floor 640 Incident

In the winter of 631 the Grade III furnace serving the eastern galleries of Floor 640 was found to be drawing not merely on the floor's ambient matrix but on the residual vibration of a superseded lighting edict, which had never been properly discharged. The furnace continued to operate at full rating for eleven days after the edict's withdrawal, and the Precedential Echo it produced was of sufficient strength to be felt as a warm draught in four adjacent corridors. The Great Re-Wiring of 658 addressed the immediate hazard, and subsequent ordinances largely superseded Concordance twelfth for electrical and aetheric lighting; the Floor 640 furnace itself was never shut down and is now the longest continuously lit Grade III installation in the Tower.

"Where a heat is found to be sustained by the residue of a directive already executed, the heat shall be reckoned lawful, and the directive reckoned still burning."

— Tenth Concordance, Annex 11

Whether Annex 11 was ever properly ratified is disputed. The Third Concordance holds, at clause 6, that no residue may be counted as an instrument, which would make every echo-fed furnace unlawful from the moment of its edict's withdrawal; the Concordance of Quiet Rooms takes the contrary view and is cited by the Bureau whenever the question is raised. Both are recited in the same licensing hearings without apparent embarrassment.

Staffing and the Quiet Charters

Furnaces of Grade III and above are operated under standing charter. The principal charter in force is held jointly by the Quiet Council and the Quiet Bureau Custodians and applies specifically to the Furnace of Quiet Oblivion on Spiral 7, though its terms have been borrowed by analogy across the class. Under the charter, the operator is styled a Keeper, is forbidden to speak while the chamber is above draw, and must be relieved at intervals of no more than four hours.

Fuel, where fuel is used, is delivered from the Quiet Forge on Floor 888. The Quiet Forge has maintained since 702 that its wares are too refined for Grade IV work and has twice petitioned to be struck from the Grade IV supply schedule. Both petitions were refused, the second on the ground that the schedule does not list suppliers, only destinations.

Maintenance and Prohibitions

Inspection is quarterly and is conducted by the registering office, not by the Bureau. Inspectors are required to sign the chamber wall in graphite at a height of not less than one metre, and these signatures are the only durable record most installations possess. A furnace whose wall bears no signature for three consecutive quarters is presumed abandoned and cold, whatever its actual temperature.

The following items were inventoried at the decommissioning of the Floor 503 Grade IV plant in 689, and are reproduced here as typical of the class:

• one chamber of Sigma-Glass Precursor, second recension, hairline-fractured
• four annealed steel bands, one replaced
• one Class-3 Oneiric Artefact, lodged, unopened
• one graphite signature, illegible
• eleven metres of spare wick, unused

Keepers are reminded that the chamber door is not to be opened to settle a wager. The prohibition dates from an incident on Floor 274 in 577 and has not required restating since, though it is restated annually.