Planck's law In 1880, André-Prosper-Paul Crova published a diagram of the three-dimensional appearance of the graph of the strength of thermal radiation as a function of wavelength and temperature. He determined the spectral variable by use of prisms. He analyzed the surface through what he called "isothermal" curves, sections for a single temperature, with a spectral variable on the abscissa and a power variable on the ordinate. He put smooth curves through his experimental data points. They had one peak at a spectral value characteristic for the temperature, and fell either side of it towards the horizontal axis. Such spectral sections are
Abscissa and ordinate (Latin; "linea abscissa", "a line cut off") has been used at least since "De Practica Geometrie" published in 1220 by Fibonacci (Leonardo of Pisa), its use in its modern sense may be due to Venetian mathematician Stefano degli Angeli in his work "Miscellaneum Hyperbolicum, et Parabolicum" of 1659. In his 1892 work "Vorlesungen über Geschichte der Mathematik, Volume 2," (""Lectures on history of mathematics"") German historian of mathematics Moritz Cantor writes In a somewhat obsolete variant usage, the abscissa of a point may also refer to any number that describes the point's location along some path, e.g. the parameter of