If instantaneous monitoring is not feasible, then a 15-minute time weighted average is used. The emission of absorbed energy as light as the result of a chemical reaction. This occurs in thousands of compounds both organic and inorganic. Chemical glow sticks and fireflies are examples of this. This measurement means that for every centimeter of base length, the length will change X centimeters for every change of one degree centigrade.
Convection results from the differences in the densities of a material at different temperatures.
As a liquid or gas raises in temperature, it becomes less dense and thus lighter thereby rising above its cooler and denser counterparts, which in turn sink.