Mostly testimonial letters from satisfied clients of A.P. Watt, praising his services. Many of the letters were published in promotional brochures. Two of these books, COLLECTION OF LETTERS ADDRESSED TO A.P. WATT BY VARIOUS WRITERS (London, 1893) & LETTERS ADDRESSED TO A.P. WATT (London, 1894), are included in the collection. There were other editions published in 1889, 1898, 1899, 1924, 1929, etc.