Jevons's own pedagogical textbook, Elementary Lessons in Logic, describes the Logic Piano in Lesson XXIII (pp.191–201) — sixty to seventy pages past the lessons Aikins quotes to the page
Lesson XXIII of Jevons's Elementary Lessons in Logic ("Boole's System of Logic," pp.191–201 of the 1881 Macmillan "New Edition") walks from the "Method of Indirect Inference" — the same elimination principle [[claim-jevons-derived-logic-machine-from-indirect-inference|derived the machine in The Substitution of Similars]] — through a "logical slate" and a "Logical abacus," to: "More recently however I have reduced the system to a completely mechanical form, and have thus embodied the whole of the indirect process of inference in what may be called a Logical Machine," describing its keyboard ("21 keys like those of a piano") and dating its debut: "An account of this logical machine may be found in the Proceedings of the Royal Society for Jan. 20th, 1870, the machine having on that day been exhibited in action to the Fellows of the Society." This independently corroborates, from a third Jevons text, the date already fixed at Tier 1 in claim-jevons-1870-paper-received-16-oct-1869-read-20-jan-1870-royal-society and the machine identity in claim-jevons-logic-piano-1869-mechanical-inference-machine.
The load-bearing point is locational: this passage sits in the same physical, stereotyped-reprint book — see entity-elementary-lessons-in-logic-jevons and claim-jevons-elementary-lessons-1881-printing-toc-confirms-stable-pagination-since-1870 — as the Lesson X (pp.81–87) and Lesson XV (pp.126–131) passages Aikins quotes to the page in 1902 (see claim-jevons-elementary-lessons-lesson-x-source-of-aikins-conversion-rule-citations, claim-jevons-elementary-lessons-lesson-xv-source-of-aikins-eight-syllogism-rules). Lesson XXIII comes later in the book than both — under the thematic heading "RECENT LOGICAL VIEWS," two blocks past "SYLLOGISM." Whatever explains Aikins's silence on the machine, it is not that the machine belonged to a separate technical paper outside the book he was already citing to the page.
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“More recently however I have reduced the system to a completely mechanical form, and have thus embodied the whole of the indirect process of inference in what may be called a Logical Machine.”
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