“"Elementary, my dear Watson, elementary," murmured Psmith. (Earlier usage of the precise words "Elementary, my dear Watson" has been found in the works of Sir Arthur Conan Doyle.)”

Source: The Thirteenth Tale

Source: Wishful Thinking: A Theological ABC

Source: Sherlock Holmes: The Complete Novels and Stories, Volume I

Letter to William Sotheby (13 July 1802).
Letters
Context: Metaphisics is a word that you, my dear Sir! are no great friend to / but yet you will agree, that a great Poet must be, implicitè if not explicitè, a profound Metaphysician. He may not have it in logical coherence, in his Brain & Tongue; but he must have it by Tact / for all sounds, & all forms of human nature he must have the ear of a wild Arab listening in the silent Desart, the eye of a North American Indian tracing the footsteps of an Enemy upon the Leaves that strew the Forest —; the Touch of a Blind Man feeling the face of a darling Child.

Source: 1960-70's, Prospectus et tous écrits suivants, 1967, pp. 203-204

Duhamel, Cours d'Analyse de l'Ecole Polytechnique. Paris, Bachelier. vol i 1841 vol. ii. 1840.
The Differential and Integral Calculus (1836)

Letter XI
Evelina (1778)

Preface, p. iii
The Differential and Integral Calculus (1836)