A Manual Of Photography

20 HISTORY OF PHOTOGRAPHY. an object, so as to have pretty distinct outlines, when I employed the full sunshine, was half a second.” This is to be understood of toe paper then used by Mr. Talbot for taking objects by means of the solar microscope. In the Philosophical Magazine, Mr. Fox Talbot published the hrst account of his Photogenic experiments. This term was in- troduced by this gentleman : and his experiments cannot be bettei described than in his own words. “In order to make what may be called ordinary photogenic paper, I select, in the hrst place, paper of a good firm quality and smooth surface. I do not know that any thing answers better than superfine writing paper. I dip it into a weak solution of common salt, and wipe it Oywhieb the salt is uniformly distributed throughout its sub- stance. I then spread a solution of nitrate of silver on one surface only, and dry it at the fire. The solution should not be saturated, but six or eight times diluted with water. When dry the paper is fit for use. I have found by experiment that there is a certain proportion betveen the quantity of salt and that of the solution of silver which ansivers best, and gives the maximum effect. If the strength of the salt is augmented beyond this point, the effect diminishes, and, in certain cases, becomes exceedingly small. “ This paper, if properly made, is very useful for al1 pho- togenic purposes. For example, nothing can be more perfect tiian the images it gives of leaves and flowers, especially with a summer sun,—the light passing through the leaves, delineates every ramification of their nerves. “^ow, suppose we take a sheet thus prepared, and wash it with asaturated solution of salt, and then dry it. We shall find (especially if the paper is kept some weeks before the trial is made) that its sensibility is greatly diminished, and, in some cases, seems quite extinct. But if it is again washed with a liberal quantity of the solution of silver, it becomes again sen- sible to light, and even more so than it was at first. In this way by alternately washing the paper with salt and silver, and drying it between times, I have succeeded in increasing its sensibility to the degree that is requisite for receiving the images of the camera obscura.’. £ In conducting this operation, it will be found that the results are sometimes more and sometimes less satisfactory, in conse- quence of small and accidental variations in the proportions employed. It happens sometimes that the chloride of silver is disposed to darken of itself without any exposure to light: this shows that the attempt to give it sensibility has been carried too far. The object is to approach to this condition as near as possible without reaching it, so that the substance may be in a state