The first studies by Nobili and Melloni on the properties of different substances to emit, absorb, transmit and reflect radiant heat were presented to the Academy of Science in Paris on 5 September 1831.
Melloni's later experiments established the perfect analogy between the behaviour of heat radiation (infrared) and light radiation as concerns linear propagation, reflection, refraction and polarization, but also established the perfect identity of the laws governing such phenomena for the two kinds of radiation. In his La Thermochrôse ou la coloration Calorifique (of which only the first of the two planned volumes was published) Melloni stated: "I was ever convinced that there should be important differences between them, but what these differences were, I searched for in vain."
The systematic studies performed by Melloni and those performed in 1847 by the French scientists Armand Hippolyte Louis Fizeau (1819-1896) and Jean Bernard Léon Foucault (1819-1868) who, they too using a thermomultiplier, confirmed the undulatory nature of heat radiation by producing interference phenomena, and conclusively and conclusively demonstrated the identity of all radiations of the electromagnetic spectrum then known. ...continues