30 LIGHT-PAINTING. 



paitly transparent and partly opake, such as the wings of insects, leaves 

 &c., by transmitting the light through them upon paper, upon which a 

 weak solution of the nitrate of silver had been brushed. The paper 

 opposite the opake parts remained white, whilst that opposite the trans- 

 parent parts was blackened. But the difficulty was, that unless these 

 copies vv^ere kept in the dark the whole paper was blackened and the 

 copy lost. 



Ko further piactical use was made of the knowledge of these effects 

 of light, until about eight or nine years since, when Daguerre, a French- 

 man, announced the interesting discovery of a process by which perma- 

 nent copies of material objects could be taken on the surface of a plate 

 of silver. Tbe secret of a process so wonderful, and likely to prove 

 so useful in its applications, was at once purchased by the French Gov- 

 ernment for a large sum and with true liberality, made known as the 

 property of the world. The art as made known by him, and which 

 has been made to bear the very awkward name of '•'Daguerreotype," 

 was brought to a wonderful degree of perfection. The plate, which 

 might be one of copper thinly coated witli silver, was well cleaned and 

 polished, first with tripoli powiler and alcohol, and then with rouge ; it 

 was next exposed for a few moments to the vapor of iodine contained 

 in a close wooden box having an opening in the top of the size of the 

 plate ; when it had acquired a golden yellow color, which was owing 

 to the formation of a very thin film of the iodide of silver, it was trans- 

 ferred, carefully protected from the light, to a Camera Obscura, whose 

 focus was previously arranged so as to throw the image of the object 

 to be copied precisely at the place which the plate should occupy; and 

 after remaining there for about five minute."!, less or more according to 

 the strength of illumination, it was transferred to a box containing mer- 

 cury^ to whose vapors it was exposed for a short time until the picture 

 appeared.. The action of the light alone is not sufficient, as in the case 

 of the nitrate of silver above mentioned, to make the picture to appear 

 upon the coaling of the iodide. The light, it seems, is not able entirely 

 to decompose the iodide, for no iodine is set free in the Camera ; but 

 merely to produce in it a certain change, v^hich, by the subsequent aid 

 of the mercury, is completed. The mercury, by its attraction, with- 

 draws the iodine, and unites with the silver of that portion of the io- 

 dide of silver acted upon by the light, forming with the latter a white 

 amalgam of silver. Hence those parts of the plate most exposed to 

 the light are whitened with this amalgam, those less exposed are less 

 whitened, and those not exposed at all have merely the iodine with- 

 drawn and the dark polished surface of .silver restored. These pictures 



