132 ANNUAL OF SCIENTIFIC DISCOVERY. 



on its axis as rapidly as possible. When it had attained its greatest 

 velocity, an electric battery was discharged in front of the disc, light- 

 ing it up with a momentary flash. A camera, containing a very sensi- 

 tive plate of glass, had been placed in a suitable position, and on 

 opening this after the discharge, an image was found of a portion of 

 the words printed on the paper. They were perfectly well-defined and 

 wholly unaffected by the motion of the disc. 



" The mode of preparing the plates was as follows : 1. Take the most 

 liquid portion of the white of an egg, rejecting the rest. Mix it with 

 an equal quantity of water. Spread it very evenly upon a plate of 

 glass, and dry it at the fire. A strong heat may be used without 

 injuring the plate. The film of dried albumen ought to be uniform and 

 nearly invisible. 2. To an aqueous solution of nitrate of silver add a 

 considerable quantity of alcohol, so that an ounce of the mixture may 

 contain three grains of the nitrate. I have tried various proportions, 

 from one to six grains, but perhaps three grains answer best. More 

 experiments are here required, since the results are much influenced 

 by this part of the process. 3. Dip the plate into this solution, and 

 then let it dry spontaneously. Faint prismatic colors will then be 

 seen upon the plate. It is important to remark, that the nitrate of 

 silver appears to form a true chemical combination with the albumen, 

 rendering it much harder, and insoluble in liquids which dissolved it 

 previously. 4. Wash with distilled water to remove any superfluous 

 portions of the nitrate of silver. Then give the plate a second coating 

 of albumen similar to the first ; but, in drying it, avoid heating it too 

 much, which would cause a commencement of decomposition of the 

 silver. 5. To an aqueous solution of prot-iodide of iron add first an 

 equal volume of acetic acid, and then ten volumes of alcohol. Allow 

 the mixture to repose two or three days. At the end of that time it 

 will have changed color, and the odor of acetic acid, as well as that of 

 alcohol, will have disappeared, and the liquid will have acquired a 

 peculiar but agreeable vinous odor. It is in this state that I prefer to 

 employ it. 6. Into the iodide thus prepared and modified the plate is 

 dipped for a few seconds. All these operations may be performed by 

 moderate daylight, avoiding, however, the direct solar rays. 7. A solu- 

 tion is made of nitrate of silver, containing about 70 grains to one 

 ounce of water. To three parts of this add two of acetic acid. Then, 

 if the prepared plate is rapidly dipped once or twice into this solution, 

 it acquires a very great degree of sensibility, and it ought then to be 

 placed in the camera without much delay. 8. The plate is withdrawn 

 from the camera, and, in order to bring out the image, it is dipped into 

 a solution of protosulphate of iron, containing one part of the saturated 

 solution diluted with two or three parts of w r ater. The image appears 

 very rapidly. 9. Having washed the plate with water, it is now 

 placed in a solution of hyposulphite of soda ; which, in about a minute, 

 causes the image to brighten up exceedingly, by removing a kind of 

 veil Avhich previously covered it. 10. The plate is then washed with 

 distilled water, and the process is terminated. In order, however, to 

 guard against future accidents, it is well to give the picture another 

 coating of albumen or of varnish. 



