Note 13 — Chapter I

Professor Stokes wrote me in the following flattering terms:—“What you have submitted to me on the subject of apertures is so sound, clear, and succinct, that I have nothing to add to it. The method adapted as you have explained respecting the immersion system, I consider to be perfectly satisfactory.” Subsequently, and at my request, Sir George Stokes contributed a valuable paper on the subject to the “Transactions of the Royal Microscopical Society,” 1876, on “The Theoretical Limit of Aperture.”