The correspondence is dated 1788, 1792, 1800, 1802, 1806, 1808-1821. Since John Rennie always used Boulton and Watt's engines, and Boulton and Watt Rennie's mill work, the bulk of this correspondence is to be found with the papers relating to specific undertakings. This volume contains miscellaneous and personal material, but it does include the letters from James Watt junior on his trip up the Rhine in the steam ship 'Caledonia' in 1817. It also contains (folio 1) a copy of the patent granted to James Watt senior in 1775.