The nature of heat

The nature and effects of heat have intrigued philosophers and scientists since ancient times. Different theories were developed to explain the phenomena, and of these, the wave theory and the caloric theory were the ones that remained in force until the second half of the nineteenth century when overwhelming evidence led to the conclusion that heat was not a material substance, that the molecules of a gas were not stationary but could move in space, and that radiation and light were basically the same phenomena.