If we take a large picture for the stereoscope, we are compelled by pictorial truth to place it at a distance from the eye equal to the equivalent focal distance of the camera. Every picture in every camera has the same apparent magnitude as the object which it represents; whether it be a human figure, or the most distant landscape; and if we desire to see it in its true relief in the stereoscope, we must place it at a distance from the eye equal to the focal length of the lens, whether it be an inch or a foot high. There is, therefore, nothing gained by using large pictures. There is, on the contrary, much inconvenience in their use. They are in themselves less portable, and require a larger stereoscope; and we believe, no person whatever, who is acquainted with the perfection and beauty of the binocular slides in universal use, would either incur the expense, or take the trouble of using pictures of a larger size. In the beautiful combination of lenticular stereoscopes, which was exhibited by Mr. Claudet, Mr. Williams, and others, in the Paris Exhibition, and into which six or eight persons were looking at the same time, binocular pictures of a larger size could not have been conveniently used. But, independently of these reasons, the question of large pictures has been practically settled. No such pictures are taken by the Daguerreotypists or Talbotypists, who are now enriching art with the choicest views of the antiquities, and modern buildings, and picturesque scenery of every part of the world; and even if they could be obtained, there are no instruments fitted for their exhibition. In the magnificent collection of stereoscopic pictures, amounting to above a thousand, advertised by the London Stereoscopic Company, there are no fewer than _sixty_ taken in Rome, and representing, better than a traveller could see them there, the ancient and modern buildings of that renowned city. Were these _sixty_ views placed on the sides of a revolving polygon, with a stereoscope before each of its faces, a score of persons might, in the course of an hour, see more of Rome, and see it better, than if they had visited it in person. At all events, those who are neither able nor willing to bear the expense, and undergo the toil of personal travel, would, in such a panorama,—an analytical view of Rome,—acquire as perfect a knowledge of its localities, ancient and modern, as the ordinary traveller. In the same manner, we might study the other metropolitan cities of the world, and travel from them to its river and mountain scenery,—admiring its noble castles in our descent of the Rhine,—its grand and wild scenery on the banks of the Mississippi, or the Orinoco,—the mountain gorges, the glaciers, and the peaks of the Alps and the Ural,—and the more sublime grandeur which reigns among the solitudes of the Himalaya and the Andes.