Other meanings of Macedonio Melloni
Physics
Macedonio Melloni (1798–1854) was an Italian physicist whose pioneering research on infrared radiation established the foundations of thermal spectroscopy. He is best known for inventing the thermomultiplier, a highly sensitive device that allowed precise measurement of radiant heat, and for demonstrating that infrared light obeys the same laws of reflection, refraction, and polarization as visible light.1
Melloni was born in Parma, then part of the Duchy of Parma, on April 11, 1798. He studied at the University of Parma, where he developed an early interest in physics and chemistry. After graduating, he worked as a professor of physics at the University of Parma and later at the University of Florence. His early research focused on electricity and magnetism, but he soon turned to the study of radiant heat, a field that was still in its infancy.2
In 1831, Melloni fled political unrest in Parma and settled in Paris, where he collaborated with the French physicist François Arago. His exile proved fruitful: he gained access to better laboratories and began his most important experiments on the transmission of heat through various materials.3
Melloni's most celebrated achievement was the invention of the thermomultiplier, developed in 1831 with Leopoldo Nobili. This device combined a thermopile with a sensitive galvanometer, enabling detection of temperature differences as small as 1/100 of a degree Celsius. With it, Melloni could measure the intensity of infrared radiation with unprecedented precision, effectively creating the first thermal spectrometer.4
Using the thermomultiplier, Melloni systematically studied the transmission of radiant heat through dozens of substances, including rock salt, glass, and quartz. He discovered that rock salt (sodium chloride) is highly transparent to infrared radiation, while glass blocks much of it — a finding that contradicted earlier assumptions and laid the groundwork for infrared spectroscopy.5
Melloni demonstrated that infrared radiation exhibits the same optical properties as visible light: it can be reflected, refracted, polarized, and diffracted. He also showed that the heating effect of different wavelengths varies, and he introduced the concept of 'diathermancy' (transparency to heat) to describe how different materials transmit radiant energy.6
His work earned him the Rumford Medal from the Royal Society in 1839, and he was elected a foreign member of the Royal Society in 1840. In 1839, he published his magnum opus, La Thermochrôse, ou la coloration calorifique, which summarized his experiments and theories on radiant heat.7
Beyond his main achievements, Melloni made several lesser-known contributions. He was among the first to measure the heat from the moon and stars using his thermomultiplier, a feat that impressed contemporaries and hinted at the potential of infrared astronomy.8
Melloni also developed a method for detecting water vapor in the atmosphere by analyzing its infrared absorption, an early precursor to modern remote sensing. He was an early advocate for the wave theory of light, supporting the work of Augustin-Jean Fresnel against the particle theory. His later years were marred by political turmoil; he returned to Italy in 1848 and became a senator of the Kingdom of Sardinia, but his health declined, and he died in Portici in 1854.2
Melloni's work bridged the gap between optics and thermodynamics, influencing later scientists such as John Tyndall and Gustav Kirchhoff.
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