Faraday's own preface immediately clarifies the nature of this volume: it is a reprint of fourteen series of papers published in the Philosophical Transactions between 1831 and 1838, assembled at the request of readers. He emphasizes that the work was written in parts, with earlier portions rarely anticipating later ones, and that he has made only typographical or grammatical alterations, adding footnotes dated December 1838 to correct errors. This editorial note sets the expectation that the text proceeds as a chronological record of discovery rather than a unified treatise.

The excerpts show Faraday's characteristic method: numbered paragraphs (e.g., 990–994) build arguments from experimental evidence, with careful definitions of terms like 'intensity' and 'quantity' of electricity. His reasoning is quantitative, linking the amount of zinc oxidized to the electricity produced, and he explicitly connects his findings to earlier work by others, as in paragraph 992.

A Chronological Record, Not a Unified Treatise

Faraday's preface is essential for a first-time reader. He states plainly that the volume was not written as a whole, but in parts, and that earlier portions rarely had any known relation to later ones. This means the reader should expect shifts in focus and terminology as Faraday's understanding evolved. He also notes that he has added footnotes (dated Dec. 1838) to correct errors, which are distinct from the original notes. These footnotes provide a retrospective view, showing where Faraday later revised his earlier claims. The preface thus functions as a roadmap: the text is a faithful reprint, not a polished monograph, and the reader should attend to the dates of each series.

Numbered Paragraphs and Experimental Precision

The excerpts reveal Faraday's systematic use of numbered paragraphs (e.g., 990–994) to build arguments step by step. Each paragraph often contains a single experimental result or logical inference, making the reasoning easy to follow. For example, paragraph 990 explains that the quantity of electricity in a current cannot be increased by adding more cells, only the intensity. This is supported by a concrete experiment in paragraph 991, where ten pairs of plates produced the same quantity of hydrogen at each platina plate as a single pair. Faraday also references earlier paragraphs (e.g., 868, 924, 949) to connect his findings, creating a dense web of cross-references. Readers should be prepared to follow these links to understand the full argument.

The Central Concept: Definite Electro-chemical Action

A recurring theme in the excerpts is the principle of definite electro-chemical action. Faraday states in paragraph 990 that 'the quantity of electricity passed and the quantity of electrolyte decomposed, must be the equivalents of each other.' This is a quantitative law, and he supports it with experimental evidence: a single pair of zinc and platina plates throws as much electricity into a current by oxidizing 32.5 grains of zinc as would be circulated by a thousand times that quantity in a battery. The excerpts do not reveal the full derivation of this law, but they show Faraday's method of measuring and comparing quantities. The reader should watch for how this principle is applied to explain the behavior of batteries and electrolysis throughout the series.

Intensity vs. Quantity: A Key Distinction

Faraday carefully distinguishes between the 'intensity' and 'quantity' of electricity. In paragraph 990, he explains that adding more cells in a battery increases intensity without increasing quantity beyond that proportionate to the zinc oxidized in a single cell. This distinction is crucial for understanding why a battery can decompose electrolytes that a single pair cannot (paragraph 993). The excerpts do not define intensity explicitly, but Faraday's usage suggests it relates to the ability to overcome chemical affinities. Readers should note that this terminology may differ from modern usage, and that Faraday is developing these concepts as he goes. The experimental proof in paragraph 991, using a magnetic needle, shows that the deflecting power of a single pair equals that of the whole battery, confirming the quantity is the same.

Approach this volume as a series of research papers rather than a textbook. Faraday's preface encourages the reader to see the work as a faithful record of his investigation's course and results. Pay attention to the dates of each series and the footnotes, which offer later corrections. The numbered paragraphs and cross-references reward careful reading, and the quantitative experiments provide concrete anchors for the theoretical arguments. This is a work of discovery in progress, and the reader is invited to follow Faraday's reasoning as it unfolds.