1857. unbound. 1 page, 10 x 8 inches, no place, August 8, 1857. Rare and early autographed letter signed by the Swedish-born American engineer and inventor of advances in ship-building, regarding his "caloric" (steam) engine invention, in part: "...Of course we cannot test our obion system unless we have a boat that will float in open water and, if we fail, you then meant, a tight boat to put the caloric engine into..." Blind-stamped in the upper left corner. Blue wax-crayon checkmark through the date; light glue stain on the back; natural folds. Very good(-) condition.