IR thermometry: then and now

摘要

In 1800 William Herschel, the great astronomer and telescope maker, tried an experiment. Like Newton in 1666, he passed a beam of white light through a glass prism and found, spread out before him, the familiar spectrum of colours, from violet to red. Unlike Newton, he placed a thermometer at various points along the spectrum and, as he suspected, found that the temperatures differed. The lowest were at the violet end of the spectrum and they rose toward the red and then, beyond the end of the spectrum, they kept rising. Not only had Herschel proved what he had set out to prove (that light and radiant heat are identical, itself a momentous finding) but he had discovered infrared radiation extending beyond the end of the visible spectrum. As the great man noted, radiant heat consists of "invisible light".