Law, Andrew. The Rudiments of Music: or A Short and Easy Treatise on the Rules of Psalmody. To which are annexed, A number of Psalm and Hymn Tunes; Fourth Edition, With the addition of a number of Pieces never before published. Cheshire, Connecticut: William Law, 1792. Fourth Edition. Leather spine, oblong plain paper-covered boards, 8 1/2 x 5 inches, boards stained, some worming to the back outer hinge. 5, , 76 plates of music, round notes in four parts. Pages show light toning but are unmarked and complete - the text is very good. Bold "Entered according to the Laws of the United States" on verso of tp. Very good. Hardcover. 
ESTC W22029; Evans 2466. ESTC locates 6 copies, all in the USA, and their listing describes the plates as being bound out of order, but our copy is without that defect. Worldcat adds 5 additional copies. Law's psalters at this period were printed by his older brother, William.
This was the last year that Law included American tunes in his collections. In 1793 he began to publicly oppose American tunes in favor of those of Europe, and his tunebooks changed to reflect that new opinion. This fourth edition was published less than a year after the appearance of the third, and differs in three ways from it: 1. The title includes the line, tunes "never before published"; 2. the introduction was expanded; and, 3. texts were added to tunes which had appeared without them in earlier editions. The new music is 10 additional tunes, 5 of which were by the Connecticut composer Rev. Alexander Gillet (1749-1826), and "their harmonic idiom leaves no doubt that they were composed by an American." - Crawford, Andrew Law, American Psalmodist, pp. 72-73.
Andrew Law (1749-1821), b. Milford, Ct; one of the first Americans to write about music and the pioneer of a shape-note system of musical notation. "Andrew Law was the most ambitious American psalmodist of the eighteenth century...He traveled the length of America, establishing singing schools in eleven states; he devised an original musical notation; he was the first American musician to become actively interested in copyright legislation; and, though not primarily a composer, he was his generation's most prolific compiler of tunebooks, publishing, in all, more than thirty separate items." - ibid., preface pp. xv.-xvi.