This is the oldest example of an infrared photograph I’ve seen. Searching around on the net gives me conflicting information about the date infrared photography developed. One source says that Kodak introduced infrared film in 1922. Another source says that infrared light was discovered in 1903, but that seems unlikely—yet another says that Hershel discovered it in 1800—that seems plausible. I found out a bit more about the energiatype developed by Hunt—he publicized the process in 1844, claiming that it worked with a type of energy as yet undiscovered—which, as it turns out, is ultraviolet light. X-rays were discovered around 1897 I think, so it seems like the nineteenth century was obsessed with invisible rays.
The most interesting stuff I found to-day has more to do with the identity of the photographer who took this picture. He was a famous optician at John Hopkins University, Robert W. Wood. He’s most well known, it seems, for debunking N-rays. One site called him “the P.T. Barnum of physics.” He was known for his practical jokes, but I liked this anecdote the best. It seems that his basement laboratory was filled with cobwebs and cockroaches. He was doing an experiment that involved a long light-baffle that had become covered in cobwebs. He borrowed a friends Persian cat, and a can of tuna. Wood set the open can of tuna at one end of the baffle, and the cat at the other. The cat then walked through the baffle, neatly clearing away the cobwebs.
Wood was also known for another eccentricity. After a rainstorm, he would carry small pellets of sodium wrapped in his pocket. He would spit in the puddles and drop in the sodium pellet at the same time. The resulting small flame convinced everyone that he was spitting fire.