---
title: "Verify the dates and details of Jevons's Logic Piano — built 1869, exhibited before the Royal Society 1870 — against a primary or scholarly source"
type: "question"
status: "open"
writer_model: "claude-opus-4-8"
date_raised: "2026-07-12T00:00:00.000Z"
tags: ["verification","jevons","logic-machines","history-of-computing","logic-piano","unverified-quant"]
---


[[claim-jevons-logic-piano-1869-mechanical-inference-machine]] rests on Tier-4
Wikipedia for its two load-bearing dates: the machine was "built from his
specifications in 1869" and exhibited before the Royal Society in 1870. Under
the sources.md escalation rule, a surprising and load-bearing historical claim
should not stay on a tertiary source.

**What to read / pull:**
- Jevons's own writings on the machine (his 1870 paper "On the Mechanical
  Performance of Logical Inference," *Philosophical Transactions of the Royal
  Society*) — the primary that would confirm both the mechanism and the 1870
  Royal Society exhibition.
- A scholarly history of logic machines (e.g. Martin Gardner, *Logic Machines
  and Diagrams*) for the 1869 construction date and the Marquand connection.

**What it gates:** moving the note off `seedling` / clearing its
`[unverified-quant]` flag. Also confirms the setup for
[[observation-jevons-double-bridge-victorian-logic-machine-to-ai-energy]].

**Update 2026-07-12 (headless), from sibling capture
`10-inbox/raw/2026-07-11-hop-jevons-logic-piano.md`:** two Tier-2
history-of-computing secondaries now corroborate part of this — the *Rutherford
Journal* ("in 1869 he designed and built what is conceivably the world's first
machine for doing logic inference … anticipated the contemporary computer by 80
years") supports the 1869 construction and the first-machine priority, and the
Computer History Museum supports the elimination mechanism. Both are recorded in
the note's `corroborating_sources`. This narrows the gap but does **not** close
the question: neither Tier-2 source was independently re-fetched in the headless
run, and the exact **1870 Royal Society exhibition date** still rests on the
paper's inferred venue (*Phil. Trans. Royal Society*) rather than the primary
itself. Question stays `open`; what remains is the primary — Jevons's 1870 paper
or the Royal Society record.

**Separate, lower-priority thread (not gating this note):** the
Peirce→Marquand→Shannon electrical-switching lineage mentioned as context in the
note rests on tertiary history-of-computing sites and would need Peirce's actual
30 Dec 1886 letter to Marquand to become its own claim. Left in the inbox as a
lead, not routed here.