In the year 1841, while practicing the art in St. Louis, Mo., I was at times, during the summer, much troubled with the electric influence of the atmosphere, especially on the approach of a thunder-storm. At such times I found the coating of my plates much more sensitive than when the atmosphere was comparatively free from the electric fluid, and the effect was so irregular that no calculation could counteract the difficulty. This satisfied me that electricity was in some measure an important agent in the chemical process, and it occurred to me that the element might be turned to advantage. I determined, therefore, to enter on a series of experiments to test my theory. Finding it impossible to obtain an electric machine, and unwilling to abandon the examination, it occurred to me, that the galvanic influence might answer the same purpose. I therefore proceeded to make a galvanic battery in the following simple manner. I obtained a piece of zinc about two inches long, one inch wide, and an eighth of an inch thick. On this I soldered a narrow strip of copper, about six inches long, the soldered end laid on one side of the zinc, and extending its whole length. The battery was completed by placing the zinc in a glass tumbler, two-thirds full of dilute sulphuric acid, strong enough to produce a free action of the metals. The upper end of the copper slip extending above the tumbler was sharpened to a point, and bent a little over the glass. The method of using, was thus:--After preparing the plate in the usual manner and placing it in the camera, in such manner as to expose the back of the plate to view, the battery was prepared by placing the zinc in the acid, and as soon as the galvanic fluid began to traverse (as could be known by the effervescence of the acid, operating on the zinc and copper) the cap of the camera was removed, and the plate exposed to the sitter; at the same instant the point of the battery was brought quickly against the back of the plate, and the cap replaced instantly. If the plate is exposed more than an instant after the contact the picture will generally be found solarized. By this process I have taken pictures of persons in the act of walking, and in taking the pictures of infants and young children I found it very useful. Very respectfully yours, THOMAS R. WHITNEY. CHAP. VII PAPER DAGUERREOTYPES.--ETCHING DAGUERREOTYPES. Mr. Hunt describes a process, discovered by himself by which the Daguerrean art may be applied to paper. His description is as follows:--