On January 12th, 1820, John Herschel, a British astronomer, mathematician, and chemist, made a groundbreaking discovery that would change the course of photography. Herschel was experimenting with various chemicals in his laboratory when he stumbled upon the photographic properties of sodium thiosulfate, commonly known as "hypo."

Herschel found that this compound could dissolve silver salts, which were used in the early photographic processes. By using sodium thiosulfate as a fixing agent, he was able to make photographs permanent and prevent them from fading or darkening over time. This discovery was a significant milestone in the history of photography, as it allowed photographers to create stable, long-lasting images.

Herschel's findings were published in his paper, "On the Hyposulphurous Acid and its Compounds," which he presented to the Royal Society of Edinburgh. His work laid the foundation for the development of modern photographic techniques and helped establish photography as a viable and reliable means of capturing images.

Interestingly, Herschel also coined the term "photography" itself, deriving it from the Greek words "photos" (light) and "graphein" (to draw or write). His contributions to the field of photography extended beyond his discovery of the fixing agent; he also experimented with various photographic processes, including the cyanotype, which produces distinctive blue-tinted prints.

John Herschel's discovery of the photographic fixing agent on January 12th, 1820, was a pivotal moment in the history of science and photography. His work not only made it possible to create permanent photographs but also paved the way for the development of this revolutionary medium that has transformed the way we capture, preserve, and share visual information.