Experiments on the Refrangibility of the Invisible Rays of the Sun

William Herschel's Experiments on the Refrangibility of the Invisible Rays of the Sun is the original primary paper, published in the Philosophical Transactions of the Royal Society of London, in which Herschel reported detecting heating rays beyond the red end of the visible spectrum, the discovery that would later be named infrared radiation. As the actual founding document of the discovery, written by the astronomer who made it and published through the Royal Society's own long standing peer review process, it carries the strongest possible authority for what Herschel himself observed and how he described it. Its limit is that it is an eighteenth century primary source using the scientific vocabulary and instruments of its own time, so a claim about the modern physical understanding of infrared radiation, as opposed to the history of its discovery, needs a modern physics source rather than this paper itself.