v. 1. Academies of complement, 1680-1805
v. 2. Secretaries, 1687-1760
v. 3. Complete letter-writers, 1740-1795
v. 4. The Art of correspondence, 1770-1810.
OBNB doesn't sell books, but you may be able to find a copy at one of these websites:
British and American letter manuals, 1680-1810. ISBN 9781851969180. Published by Pickering & Chatto in 2008. Publication and catalogue information, links to buy online and reader comments.
