Seeing History in the Spectrum of Light

As I strayed into the study of an eminent physicist, I observed hanging against the wall, framed like a choice engraving, several dingy, ribbon-like strips of, I knew not what... My curiosity was at once aroused. What were they? ... They might be shreds of mummy-wraps or bits of friable bark-cloth from the Pacific, ... [or] remnants from a grandmother's wedding dress... They were none of these... He explained that they were carefully-prepared photographs of portions of the Solar Spectrum. I s...