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4to (260 x 204 mm). xxiv, 280, [16] pp., including half-title; text illustration, a general index and two folding engraved plates bound at the end. Bound in contemporary calf; expertly rebacked and partly recornered, spine with 5 raised bands, gilt ruling and red morocco lettering piece in 2nd compartment; boards and board edges ruled in gilt; red-dyed edges, original endpapers (wear to extremities). Light browning mostly to outer margins, minor foxing to first and final pages including titles, but generally a crisp and clean copy throughout. Provenance: Sion College library (stamp to verso of title); Maggs Bros. Ltd (slips of catalog entry loosely inserted). ---- FIRST EDITION AND EXCEPTIONALLY RARE, with only two copies in the USA (Burndy Library, Purdue Library). RHB records 3 copies only, sold at auction in 1967, 1942 and 1895. The book is a critical empirical work on electricity in which Lyon challenges the dominant electrical theories of his time and proposes alternative interpretations based on his own experiments, involving Leyden jars (the principal electrical storage devices before modern capacitors), conduction, and the behavior of electrified bodies. Lyon attempts to establish a new system of explanation that he believed was more consistent with the observed phenomena. Lyon challenged the "received theory", which refers to ideas broadly based on Franklin's one-fluid or two-fluid models, related interpretations of electrical attraction/repulsion and "electrical fire." Lyon believed these were incorrect and that his own observations pointed toward different underlying principles. By 1780, the prevailing view - largely shaped by Franklin (Experiments and Observations on Electricity, first published 1751) - held that glass is an insulator (a "non-conductor") and that electricity resides on the surfaces of glass, not within it. In the Leyden jar, the glass merely separates two conducting coatings, preventing immediate discharge. The electrical "fluid" cannot pass through glass, it only accumulates on opposite sides. This interpretation relied heavily on idealized distinctions between conductors and non-conductors. Lyon did not deny the standard experiments; rather, he focused on effects that orthodox theory treated as secondary or accidental, first a gradual discharge of Lyden jars from which he inferred that the charge must be passing through the glass itself, not merely leaking through air or along supports. Franklin explained this as imperfect insulation or leakage over surfaces; Lyon rejected this as ad hoc. Secondly, Lyon paid particular attention to experiments where electrical effects on one side of a glass plate or jar change immediately when the opposite side is modified and the response not delayed in a way that would suggest purely surface action. He argued that this immediacy implied direct transmission through the substance of the glass, rather than an action at a distance across an inert barrier. He also noted that thicker glass behaves differently from thinner glass and that different kinds of glass exhibit different electrical behaviors. For Lyon, this variability suggested that glass had material electrical properties, not merely geometric ones. An ideal insulator, in his view, should not display such dependence. Lyon argued that nature does not admit of absolute conductors or non-conductors, but that all bodies transmit electricity, differing only in degree and rate. For him, glass is not a non-conductor but a very slow conductor. This position anticipates, in a qualitative way, what would later be described as dielectric conduction and leakage currents, though without the mathematical formalism. Franklin and his followers disagreed with Lyon not because his observations were unknown, but because they prioritized operational definitions: glass does not readily transmit sparks or shocks, therefore it is a non-conductor. Further, they distinguished sharply between conduction and inducti.
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