A principle is a proposition or value that is a guide for behavior or evaluation. In law, it is a rule that has to be or usually is to be followed, or can be desirably followed, or is an inevitable consequence of something, such as the laws observed in nature or the way that a system is constructed.
if you are not aware what emissivity is defined as the ratio of the energy radiated from a material's surface to that radiated from a blackbody (a perfect emitter) at the same temperature and wavelength and under the same viewing conditions. it is a dimensionless number between 0 (for a perfect reflector) and 1 (for a perfect emitter).
it is the measure of how an object radiates heat.
the higher the emissivity “ε” the higher the temperature it emits. the perfect emitter of heat is called a “black body.”
a black body has an emissivity ε measure of 1.
for the emissivity of
therefore, water would emit more heat than of the sand.