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 continuous function the graph of such a function is a surface. The concept of the graph of a function is generalized to the graph of a relation. To test whether a graph of a relation represents a function of the first variable "x", one uses the vertical line test. To test whether a graph represents a function of the second variable "y", one uses the horizontal line test. If the function has an inverse, the graph of the inverse can be found by reflecting the graph of the original function over the line . In science, engineering, technology, finance, and