Single-Polarised Spectacles

Custody conditions

Stable at room temperature and pressure. May be handled without protection. Held in Recovery Cabinet 2, Custody Section.

No one is to wear the object, including trial fittings. No one is to view the lake surface through the right lens.

Δn is logged weekly. When the reading reaches local value the object leaves the active file and goes to long-term storage.

Recovery

Taken from float net ██ thirty-one hours after the ██ overturn. The object was delivered to us; nothing was sent down for it, and no part of the recovery crossed the interface.

Physical record

A pair of metal-framed spectacles. Frame profile, screw gauge, nose-pad wear pattern, right hinge play at 0.3 mm, and a 1.2 mm oxidation spot on the inner left temple all match the spectacles worn by Observer █ to within measurement. Sphere and cylinder are equal in both pairs; the axes agree.

One enumerable difference. The right lens of the object is a linear polariser with its transmission axis at 45° to horizontal. The left lens is plain. Neither lens of Observer █'s pair is polarising.

At recovery, Observer █'s spectacles were on Observer █'s face. They had not been lost, and have not been lost since.

There is no difference in age. Edge diffusion on the oxidation spot puts the two pairs within three months of each other.

Laboratory record

Glass composition, frame alloy, and solder are indistinguishable from locally manufactured stock by every assay run to date.

The polarising lens measured Δn 0.0007 above local glass at intake. At day 40 the offset was 0.0003. At the present rate the offset reaches zero, within instrument error, in early ██.

An attempt was made to reconstruct the illumination the lens was ground for, working back from its transmission curve. The fit produced three solutions, mutually exclusive, none excludable on the evidence. The attempt is recorded here as a failure and as an instance of the second rule: the measurements are sound and the world behind them does not follow from them.

Inference

If two things share all their properties they are one thing. Between this object and Observer █'s spectacles, the enumerable differences number one. Whether one is enough to make them two depends on who defines enough. This station does not offer that definition.

It will occur to every reader that at Δn 0.0007 a person needs only one lens polarised, and that their interface may take only one eye. That is an inference from the object and is inadmissible under the second rule. It is written down here because it is better recorded once than repeated in corridors.

Observer █ has requested transfer off Position 3. The request was granted.

Projection

Normalization will finish. The right lens will stop polarising and become plain glass, and the one enumerable difference will be gone. From that morning the two pairs will agree in every property we can measure, and by the principle set out above they will be the same pair of spectacles.

There will still be two of them on the shelf.