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
Graph of a function formula_2 itself. The graph of the function formula_10 defined by is the set the subset of formula_12 From the graph, the domain formula_14 is recovered as the set of first component of each pair in the graph formula_15. Similarly, the range can be recovered as formula_16. The codomain formula_17, however, cannot be determined from the graph alone. The graph of the cubic polynomial on the real line is If this set is plotted on a Cartesian plane, the result is a curve (see figure). The graph of the trigonometric function is If this set is plotted on a three dimensional