[Footnote 3: "I regard the prettie, greeful bard With tearfull, yet delightfull, notes complaine."--_Heliconia._ [Footnote 4: Lays of the Minnesingers.] [Footnote 5: Weekly Visitor, July, 1835.] [Footnote 6: "Night's sable birds, which plain when others sleep."--_Thaumantia._] [Footnote 7: Evening Elegy.--_Poetical Calendar._] [Footnote 8: Harleian Miscellany, vol. viii.] * * * * * PHOTOGRAPHIC CORRESPONDENCE. _Photographic Exhibition._--We understand that the Photographic Society has made arrangements for an exhibition of photographs in the metropolis during the months of January and February next. The exhibition will not be confined to the works of native photographers, but will comprise specimens of the most eminent foreign artists, who have been specially invited to contribute. From the advances which have been made in this favourite art, even since the recent exhibition in the rooms of the Society of Arts, we may confidently anticipate that the display on the present occasion will be one of the highest interest. _How much Light is obstructed by a Lens?_--Can any of your scientific correspondents furnish me with an approximation to the quantity of light which is transmitted through an ordinary double achromatic lens, say of Ross, Voightlander, or any other celebrated maker? LUX. _Stereoscopic Articles._--I cannot agree to my opponent's assumed amendment (?) (Vol. viii., p. 419.) _space_, for the simple reason that it would be virtually abandoning the whole of the points in dispute between us; when farther discussion and more mature consideration, only tend to convince me more firmly of the correctness of the propositions I have advocated, viz.: 1st. That circumstances _may_ and _do_ arise in which a better result is obtained in producing stereographs, when the chord of the angle of generation is more or less than 2-1/2 inches. 2nd. That the positions of the camera should _not_ be parallel but radial. I certainly thought that I had, as I intended, expressed the fact that I treat the cameras _precisely as two eyes_, and moreover I still contend that they should be so treated; my object being to present to each eye _exactly such a picture and in such a direction as would be presented under certain circumstances_. The plane of delineation being a flat, instead of a curved surface, has nothing whatever to do with this point, because the curves of the retinas are not portions of one curve having a common centre, but each having its own centre in the axis of the pupil. That a plane surface for receiving the image is not so good as a spherical one would be, is not disputed; but this observation applies to photographs _universally_, and is only put up with as the lesser of two evils. A plane surface necessarily contracts the field of view to such a space as could be cut out of the periphery of a hollow sphere, the versed sine of which bears but a small ratio to its chord.