In honor of John Herschel’s birthday, I would like to share this brief excerpt from the beginning of chapter 9, “Sciences of Shadow and Light.”
Thirty-three years after the fact, Margaret Herschel still recalled with photographic clarity the visit a friend of her husband’s had paid to Slough. On February 1, 1839, William Henry Fox Talbot took the new railway from London to visit John, bringing with him specimens of an ingenious method he had devised to capture images on paper. Margaret recalled that Talbot had shown the two of them “his beautiful little pictures of ferns and Laces taken by his new process.” He had produced them by placing leaves and pieces of lace on top of specially treated paper inside a wooden box covered with a glass lens, and setting the whole apparatus outside on the lawn of his estate, Lacock Abbey. The action of the sun on the light-sensitive silver chloride coating on the paper turned the areas around the objects a warm, dark brown, while the parts covered up by the leaves and lace were left a bright white–not unlike the effect of the potter Josiah Wedgwood’s jasperware, with its creamy white designs against darker backgrounds.
The problem, Talbot complained to the Herschels, was that over time the continued exposure to light would cause the images of the leaves and laces to turn a dark brown, just like the background, and the picture would be lost. He had no way to “fix” the images. Margaret remembered that her husband had said, “Let me have this one for a few minutes.” After a short time he returned, and handed the picture to Talbot, saying, “I believe you will find that to be fixed”—and thus, Margaret proudly boasted, the problem of rendering photographs permanent was solved by her husband.
Herschel had, on this telling of the story, realized with a flash that experiments he had conducted in 1819 could provide the solution. . . .