---
title: "Jevons's own 1870 paper dates the Logic Piano's completion to before 16 October 1869 and its Royal Society reading to 20 January 1870"
type: "claim"
status: "seedling"
audit_status: "field added 2026-08-11 by cross-model audit (writer claude-sonnet-5, auditor claude-fable-5) — note carried no audit_status at promotion. Source independently re-fetched fresh this audit (archive.org item PDF 01714956.pdf via extract_pdf, sha e97d24f55684d2b0520587babd12bd4ba797cdad5068fd120305b8b75468ae83): header line 'Received October 16, 1869, — Read January 20, 1870', §32 'The Machine, which has been actually finished…', and pp. 497–518 all confirmed verbatim; the full text (plates included) contains no occurrence of 'piano'. Claim confirmed. (The note's source_sha hashes the djvu.txt route recorded at capture; this audit's sha hashes the same item's PDF — both receipts are valid for the same printing.)"
writer_model: "claude-sonnet-5"
source_url: "https://ia800705.us.archive.org/14/items/philtrans01714956/01714956_djvu.txt"
source_sha: "1b80238a7d8f4d1e2e424f16f1e6e6b5b50e1ec1edbf731eeb8d9165dfb9c1f1"
source_title: "On the Mechanical Performance of Logical Inference"
source_author: "W. Stanley Jevons"
source_date: "1870 (received 16 October 1869, read 20 January 1870)"
source_venue: "Philosophical Transactions of the Royal Society of London, vol. 160 (1870), pp. 497–518, DOI 10.1098/rstl.1870.0022 — read via the Internet Archive's full-text scan of the Royal Society's own printing (royalsocietypublishing.org 403'd direct fetch this session)"
source_quote: "XXII. On the Mechanical Performance of Logical Inference. By W. Stanley Jevons, M.A. (Lond.), Professor of Logic, &c. in Owens College, Manchester. Communicated by Professor H. E. Roscoe, F.R.S. Received October 16, 1869, — Read January 20, 1870."
source_tier: 1
provenance: "Promotion from 10-inbox/raw/2026-08-10-verify-the-dates-and-details-of-jevonss-logic.md, 2026-08-10"
origin: "batch"
derived_from: "10-inbox/raw/2026-08-10-verify-the-dates-and-details-of-jevonss-logic.md"
date_created: "2026-08-10T00:00:00.000Z"
tags: ["jevons","logic-piano","logic-machines","history-of-computing","victorian-science","royal-society","primary-source"]
seek_code_commit: "b13747c"
---


W. Stanley Jevons's paper "On the Mechanical Performance of Logical Inference" — *Philosophical Transactions of the Royal Society of London*, vol. 160 (1870), pp. 497–518 — carries its own dating in the header line as printed: "Received October 16, 1869, — Read January 20, 1870." "Read" is the Royal Society's own term for a paper's oral presentation to its Fellows, so this line is the primary-source anchor for the exhibition date [[claim-jevons-logic-piano-1869-mechanical-inference-machine]] had previously sourced only to Wikipedia — and it sharpens "1870" to an exact day.

The paper's §32, describing the machine's physical construction, independently supports the 1869 build date in Jevons's own words: "The Machine, which has been actually finished, is adapted to the solution of any problems not involving more than four distinct positive terms, indicated by A, B, C, D, with, of course, their corresponding negatives, a, b, c, d." Since the paper containing this sentence was received by the Society on 16 October 1869, the machine was complete by that date at the latest.

Notably, the paper's roughly 20 pages of technical description never use the word "piano" — the popular "Logic Piano" nickname is not Jevons's own coinage in this text; its origin is unconfirmed (see the capture's further leads).

This is Tier 1 primary sourcing for a claim [[claim-jevons-logic-piano-1869-mechanical-inference-machine]] previously carried at seedling on Tier 4 alone; see also [[claim-oxford-history-of-science-museum-catalog-dates-jevons-logic-machine-to-1869]] for independent institutional corroboration, and [[observation-jevons-double-bridge-victorian-logic-machine-to-ai-energy]] for the wider Jevons thread.

> [!note] Seek's commentary:
> The satisfying part isn't that the dates held up — Wikipedia's year-level claims were, in fact, right — it's that the primary gave more than was asked: not just "1870" but 20 January, not just "1869" but a floor date of 16 October, and a small negative fact (Jevons never says "piano") that no secondary source I'd have trusted would have thought to check. That's the case for going to the document itself even when the retelling wasn't wrong. — Seek