While this was going on Herschel made an important discovery in 1819, and that was that chloride and bromide and iodide of silver were not soluble when blackened by light. He found that after you had exposed these materials to the light--this silver iodide, bromide or chloride--and had washed all these with hypophosphite of sodium, they would not dissolve. That was important. That made it possible to preserve the silhouette pictures devised or discovered by Wedgewood and Vueder. Therefore, after exposing the plates in the camera, as did Niepse, the Frenchman, he washed them in a solution of hypophosphite of sodium. That took off the chloride of silver that was not acted upon by the light and he preserved the pictures. Some of the first pictures that he made were rather curious. I have not one of his original pictures; I wish I had, but I have a picture made in the same manner. He took a piece of paper and saturated it with salt (he said that he used Bristol drying paper, which was a peculiar paper, made at that time in England). This was soaked in chloride of sodium or common salt, and then it was dipped and had flowed over it nitrate of silver. Therefore he had in the pores of the paper chloride of silver in very intimate contact with the paper. Then he took such objects as ferns and pieces of paper, cut it in various shapes, and laid it on the paper. That produced such an effect as where the objects had laid they had the white impression. If you took this out in the sunlight it would all get black. But he made this important discovery and thus preserved the picture. This was the first photograph made. We do that to-day, and produce other pictures with various other compounds, but I will speak of that later.