PHOTOGRAPHIC CORRESPONDENCE.
Photographic Experiences.—We have received from our valued correspondent Dr. Mansell, of Guernsey, a suggestion to which we are happy to give publicity, and to the promotion of which we shall be very glad to lend the columns of "N. & Q." Our photographic readers are probably aware that the Talbotype process is increasing in favour; we have recorded Dr. Diamond's strong testimony to its advantages. Mr. Llewellyn has just described his process (which is strikingly similar) in the Photographic Journal; and in a recent number of La Lumière the Vicomte Vigier confirms the views of our countrymen. Dr. Mansell, who has given our readers the benefit of his experience, well remarks that in all his acquaintance with physical science, he knows nothing more remarkable than that Mr. Fox Talbot should not only have discovered this beautiful process, but likewise have given it to the world (in 1841) in so perfect a form, that the innumerable experiments of a dozen years have done nothing essential to improve it, and the best manipulators of the day can add nothing to it. It is, however, with a view to testing some of the points in which photographers differ, so as to establish which are best, that Dr. Mansell suggests, that a table giving,
1. The time of exposure in the camera, in a bright May sun,
2. The locality,
3. The iodizement,
4. The maker of the paper,
5. The diameter of the diaphragm,
6. Its distance from the lens, and
7. The diameter, focal length, and maker of the lens,