"Meditating by one's self is like digging in the Mine; it often, perhaps, brings up maiden Earth, which never came near the Light before; but whether it contain any Metal in it, is never so well tried as in Conversation with a knowing judicious Friend, who carries about him the true Touch-stone, which is Love of Truth in a clear-thinking Head."
— Locke, John (1632-1704)
Text from Familiar Letters Between Mr. John Locke, and Several of His Friends. In Which Are Explain'd, His Notions in His Essay Concerning Human Understanding, and in Some of His Other Works, 4th ed. (London: Printed for F. Noble; T. Wright; and J. Duncan, 1742). <Link to ESTC><Link to Google Books>. ESTC note: "A reissue of the 1737 Bettesworth and Hitch edition, with the addition of the 'life', and a cancel titlepage."
See also Some Familiar Letters Between Mr. Locke, and Several of His Friends. (London: Printed for A. and J. Churchill at the Black Swan in Pater-Noster Row, 1708). <Link to ESTC><Link to Google Books>