In 1666 Isaac Newton used a prism to disperse a beam of sunlight, splitting the white light into a colored band, or the color spectrum. It consisted of the colors of the rainbow: red, orange, yellow, green, blue, indigo, and violet. For more than a century, scientists believed that the visible spectrum comprised all of the radiation emitted by the Sun. However, in 1800 the German astronomer William Herschel discovered the presence of radiation beyond the red end of the spectrum, which he called infrared light. Herschel's experiment was quite simple and easily repeated. He too used a prism to split sunlight into its component colors, projecting a spectrum upon a screen. He then passed a thermometer through the spectrum, beginning at the blue end and moving slowly toward the red, in order to determine which color transmitted the most heat energy. Herschel noted that the temperature rose...