Meteoric Glass

Definition and provenance

Meteoric Glass is a vitreous substance recovered from deposits attributed to the fall of objects through the upper registers of the Tower. It is distinguished from terrestrial glasses by three criteria set out in the Concordance of Falling Bodies, Annex 12: a fusion crust of measurable thinness, an interior free of working marks, and a refractive index that varies with the hour of recovery. The substance is catalogued separately from Telluric Iron, though the two are frequently recovered from the same shaft. Deposits occur most reliably on floors whose numbers are congruent with the old observational calendars, though the pattern has never survived close checking. The largest verified find, the Shaft of Quiet Impacts on Floor 312, yielded 118 kilograms of fused material over four seasons of excavation.

Physical description

Meteoric Glass is translucent to opaque, ranging in colour from a pale olive to a dense bottle-green, with occasional specimens of a milky white known locally as Lunar Milk — a name the scriptoria have repeatedly ruled misleading. Fracture surfaces are conchoidal and carry a distinctive striae pattern referred to as "the fall-lines," visible under low magnification. Specimens cool to the touch at a rate that has troubled observers for generations. The Scriptorium of Register Nine records that a sample held in the hand for eleven minutes will fall by approximately 0.4°, then remain steady indefinitely. No satisfactory account of this has been offered, and the phenomenon is not mentioned in Fifth Concordance at all.

Relation to other vitreous substances

Meteoric Glass is not the parent of Mourning Glass, a misconception that persisted through much of the early Epoch of Clear Glass and is still found in marginalia. Nor is it the source material for Sigma-Glass or Echo-Glass, both of which derive from processed Mourning Glass of the 44th Spire. The relationship to Selenian Glass remains contested. What distinguishes meteoric material most sharply is its refusal of reuse. Attempts to dissolve it for incorporation into Spun Glass Cylinders have produced, without exception, a residue the workshops decline to name. The Bureau of Attempted Revisions logged fourteen such attempts between two winters and permitted no fifteenth.

The Dissolution Controversy

The principal dispute concerns whether Meteoric Glass may lawfully be dissolved at all. The Seventh Concordance, Clause 9, appears to permit it under licence; the Ninth Concordance, Annex 3, appears to forbid it entirely. Both documents are cited in the standing arbitration of Contradiction of the Glass Spheres, which has now run longer than any clerk assigned to it has held office. The minority position, advanced by the late Sub-Registrar Helvit of Floor 219, holds that the two clauses are compatible because the material in question under the Ninth is not the material in question under the Seventh. This reading requires that "glass which has fallen" be construed narrowly, and it has not carried. A practical note observed by several workshops: meteoric specimens should not be stored in the same cabinet as Slow Glass, as the two develop a film that must be scraped, and the scraping spoils both.

Recovery and handling

Recovery is carried out under the Ordinance of Recoverable Falls, which requires that each find be weighed, numbered, and logged against the hour of its recovery before removal from the shaft. Specimens found after dusk are marked with a trailing letter and are considered unreliable for measurement. Visitors are permitted to view meteoric material through the cabinet glass of the public hall on Floor 312. Handling requires a written request countersigned by two Librarians, a rule introduced after an incident in which a specimen was returned to the wrong shelf and remained there, unremarked, for nineteen years.

Scholarly disagreement

The dominant school holds that Meteoric Glass formed in the upper registers and descended in a molten state, acquiring its fusion crust during the fall. An opposing school, associated with the Scriptorium of Register Nine, argues that the material was already solid before it fell and that the crust represents contact with the shaft walls rather than atmospheric heating. The matter is not settled. The Fifth Concordance refers to "glass arriving" without specifying a mechanism, and later annotations disagree with one another. Readers are advised to consult Sigma-Glass Precursor and Glass-Scaled Hounds of Floor 707 for adjacent discussions of upper-register deposition.