H. C. K.
—— Rectory, Hereford.
In reply to your correspondent J., I would ask if he has any photographic apparatus? if so, the answer to his question "What extra apparatus is required to a first-rate microscope in order to obtain photographic microscopic pictures?" would be None; but if not, he would require a camera, or else a wooden conical body, with plate-holder, &c., besides the ordinary photographic outfit. Part III. of the Microscopical Journal, published by Highley & Son, Fleet Street, will give him all the information he requires.
φ. (p. 506.) may find a solution of his difficulties regarding the production of stereoscopic pictures, in the following considerations. The object of having two pictures is to present to each eye an image of what it sees in nature; but as the angle subtended by a line, of which the pupils of the eyes form the extremities, must differ for every distance, and for objects of varying sizes, it follows there is no absolute rule that can be laid down as the only correct one. For distant views there is in nature scarcely any stereoscopic effect; and in a photographic stereoscopic view the effect produced is not really a representation to the eye of the view itself, but of a model of such view; and the apparent size of the model will vary with the angle of incidence of the two pictures, being smaller and nearer as the angle increases. I believe Professor Wheatstone recommends for landscapes 1 in 25, or about half an inch to every foot.
Geo. Shadbolt.
Cement for Glass Baths.—In reply to numerous inquiries which have appeared in "N. & Q." relative to a good cement for making glass baths for photographic purposes, I send a recipe which I copied a year or two ago from some newspaper, and which seems likely to answer the purpose: I have not tried it myself, not being a photographer.
Caoutchouc 15 grains, chloroform 2 ounces, mastic ½ an ounce. The two first-named ingredients are to be mixed first, and after the gum is dissolved, the mastic is to be added, and the whole allowed to macerate for a week. When great elasticity is desirable, more caoutchouc may be added. This cement is perfectly transparent, and is to be applied with a brush cold.
H. C. K.
—— Rectory, Hereford.