In the paper above referred to, Mr. Wheatstone says,—“I recommend, as a convenient arrangement of the _refracting_ stereoscope for viewing Daguerreotypes of small dimensions, the instrument represented, (Fig. 4,) shortened in its length from 8 inches to 5, and lenses 5 inches focal distance, placed before and close to the prisms.”[26] Although this refracting apparatus, which is simply a _deterioration_ of the lenticular stereoscope, is recommended by Mr. Wheatstone, nobody either makes it or uses it. The semi-lenses or quarter-lenses of the lenticular stereoscope _include a virtual and absolutely perfect prism_, and, what is of far more consequence, each lens is a variable lenticular prism, so that, when the eye-tubes are placed at different distances, the lenses have different powers of displacing the pictures. They can thus unite pictures placed at different distances, which cannot be done by any combination of whole lenses and prisms. [26] _Ibid._, pp. 9, 10. In the autumn of 1854, after all the facts about the stereoscope were before the public, and Mr. Wheatstone in full possession of all the merit of having anticipated Mr. Elliot in the publication of his stereoscopic apparatus, and of his explanation of the theory of stereoscopic relief, such as it was, he thought it proper to revive the controversy by transmitting to the Abbé Moigno, for publication in Cosmos, an extract of a letter of mine dated 27th September 1838. This extract was published in the _Cosmos_ of the 15th August 1854,[27] with the following illogical commentary by the editor. “Nous avons eu tort mille fois d’accorder à notre illustre ami, Sir David Brewster, l’invention du stéréoscope par réfraction. M. Wheatstone, en effet, a mis entre nos mains une lettre datée, le croirait on, du 27 Septembre 1838, dans lequel nous avons lû ces mots écrits par l’illustre savant Ecossais: ‘I have also stated that you promised to order for me your stereoscope, both with reflectors and PRISMS. J’ai aussi dit (à Lord Rosse[28]) que vous aviez promis de commander pour moi votre stéréoscope, celui avec réflecteurs et celui avec prismes.’ Le stéréoscope par réfraction est donc, aussi bien que le stéréoscope par réflexion, le stéréoscope de M. Wheatstone, qui l’avait inventé en 1838, et le faisait construire à cette époque pour Sir David Brewster lui-même. Ce que Sir David Brewster a imaginée, et c’est une idée très ingénieuse, dont M. Wheatstone ne lui disputât jamais la gloire, c’est de former les deux prismes du stéréoscope par réfraction avec les deux moitiés d’une même lentille.” [27] Vol. v. livre viii. p. 241. [28] Mr. Andrew Ross, the celebrated optician!