Lectures On Architecture. Consisting of Rules Founded upon Harmonick and Arithmetical Proportions in Building, Design'd As an Agreeable Entertainment for Gentlemen: And More particularly useful to all who make Architecture, or the Polite Arts, their Study. - Read to a Society establish'd for the Improvement of Arts and Sciences, and Explain'd, by Examples on Copper Plates; with the Proportions apply'd to Practice. - By Robert Morris. - The Second Edition. -

Part the Second contains twelve, not '13 Copper-plates', as announced on the title-page. They are unnumbered, but lettered as follows: C, C, D, E, E, F, F, [unlettered], G, G, E, I.

The number of unnumbered pages at the beginning of Part I varies from copy to copy (described by cataloguers as 14, 16 or 18).

The work was first published in 1734. It is a series of fourteen lectures read by the author 1730-1735 to a Society for the Improvement of Knowledge in Arts and Sciences, which he founded in 1730.

The lectures are in two parts - the first eight here in their second edition (they had originally been published in 1734), the final six in their first edition (with their own title page, dated 1736, and described as Part the Second). Part II is printed uniformly with the text of the first eight lectures, and paged continuously with them. The second edition of Part I is a resetting of the text of the first edition, with errata corrected, the dedication to Sir Michael Newton omitted and the advertisement changed - and the pagination made not perfectly continuous with Part II, as it now runs to 132 rather than 134 pages. Its five plates are reprints from the first edition.

The Preface of Part I states that the lectures will be on the origins of society, the advantages of learning, the history of architecture, the nature and use of the orders, siting and proportions. Fundamental to all would be the 'principle of the harmonick proportions' which the author had learned from Lambert ten Kate's treatise translated into English as The beau ideal (1732). After distinguishing the characters of the orders - the grave Doric, the 'riant uses' of the Ionic and the Corinthian suited to palaces but also to 'silent streams, the gay, the wanton scene' - Morris writes at length on harmony and proportion, drawing on observations in Shaftesbury's Characteristicks (1711) and on the musical analogies made much earlier by Alberti and Palladio (though his system of proportions is different from theirs). He suggests that there are seven fundamental architectural proportions (1:1:1 - 1:1:1½ - 1:1:2 - 1:2:3 - 2:3:4 - 3:4:5 - 3:4:6), which reflect 'the whole oeconomy of the universe'. The four plates of Part I show geometric solids, an interior composed according to four different proportions, and plans and elevations for a house on the proportion 3:4:5.

Part II consists of demonstrations. The plates show plans and elevations of seven houses - six designed according to Morris's proportions and one 'compos'd of different proportions'. The accompanying text addresses questions of proportion, ornament and location. Proportion and convenience are best achieved in a country villa - and 'such retreats would give unspeakable raptures to a soul capable to pursue a tract of thought in infinity of space, or contemplating upon the immense wonders of the universe'.