"And we must be content to rest upon the surface without straining to pierce into causes which are hidden from us, and which have hitherto mocked the attempts of impatient philosophers. We should resolve to wait till a longer fathom line is granted us, and then we shall be able to sound depths which we cannot do in our present state of frail imperfection."
— Boswell, James (1740-1795)
(p. 158 in London Magazine)
See also James Boswell, The Hypochondriack, ed. Margery Bailey, 2 vols. (Stanford UP, 1928).