History of black and white photography. After completing a lecture at the Sorbonne one day in 1827, Jean Dumas, an outstanding chemist of the period, was approached by an obviously per¬turbed woman who introduced herself as "the wife of Daguerre, the painter." Her husband, she said, was "possessed." He was convinced he could make permanent black and white pictures from the fleeting black and white images produced by a. lens. "I'm afraid he is out of his mind," she said. "Do you, as a man of science, think it can ever be done, or is he mad?" "In our present state of knowledge, it cannot be done," Dumas replied, "but I cannot say it will always remain impossible, nor set the man down as mad who seeks to do it." Dumas was not merely pacifying a worried woman; he had good reason not to dismiss the idea of recording permanent black and white images with light. As a chemist, he undoubtedly knew that certain silver compounds were reactive to light -as early as the 17th Century, an Italian scientist, Angelo Sala, had reported that "when you expose powdered silver nitrate to the sun, it turns black as ink"-and that men had already recorded short-lived black and white pictures with these compounds. The unsolved and enormously difficult problem was how to "fix" the recorded pattern, halting the reaction with light so that the black and white picture would not fade away. In 1727, a hundred years before Madame Daguerre talked with Dumas, Johann Heinrich Schulze, professor of medicine at the University of Altdorf in Germany, made the first of these ephemeral black and white pictures. One day, as part of an experiment that had nothing to do with light black and white images, he stood a flask containing a silver nitrate mixture in sunlight; when he inspected it a few minutes later, he found the part of the solution that had received the direct rays of the sun had turned a dark violet, while the remainder of the mixture retained its original whitish color. When he shook the bottle, the violet disappeared. Intrigued by this phenomenon, Schulze pasted paper stencils on the flask and faced them directly toward the sun. When he later removed the stencils, there, outlined by the surrounding darkened sediment, were the whitish patterns-i.e., negative silhouettes-of the light-blocking slips of paper. But was it the sun's light or its heat that caused the unshaded chemicals to darken? To answer that question, Schulze placed another container of the mixture in a hot, dark oven. It was not affected; obviously light had caused the change. The silhouettes were soon gone, however. Within a comparatively short time, just the reflected daylight in the room darkened them to the same shade as the surrounding sediment. In the early 19th Century, Thomas Wedgwood, the youngest son of Josiah Wedgwood, the famous British pottery manufacturer, made similar experiments with similarly tantalizing results. He made some attempts to record the natural black and white images created by a lens in a camera obscura, the ancient device that artists used, to cast a black and white picture of a scene on a glass viewing screen. The results, however, were so poor that he concentrated on making silhouettes like Schulze's, placing leaves and insect wings on silver sensitized white paper or white leather and exposing them to the sun. Like Schulze, he achieved negative black and white images. Wedgwood tried many ways to make these silhouettes permanent, but nothing worked. As soon as light, however subdued, struck the black and white images, they began to darken like the rest of the coating.