Discoverers of Different Regions of Electromagnetic Spectrum


Electromagnetic radiation has a wide range of frequencies or wavelengths. Different regions of this wide range from the shortest wavelengths to the longest ones (equivalently from the highest frequencies to the lowest ones) are respectively named gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves and radio waves. In other words, gamma rays have the highest frequencies and photon energies with the shortest wavelengths among different kinds of electromagnetic radiation while radio waves have the lowest frequencies and photon energies with the longest wavelengths and the other remaining ones lie between these two. Each of these kinds of electromagnetic radiation has different characteristics whether how they are produced, how they interact with matter or what practical applications they have. As a result, each has its own history of discovery in 19th century.


Not considering obvious visible light, the first kind of electromagnetic radiation to be discovered was infrared in 1800 attributed to William Herschel. Herschel measured temperatures of different parts of the spectrum produced by passage of sun light from a glass prism and discovered unexpected increase in the temperature of the region beyond the red part of the spectrum. The cause of heating beyond the red part of the spectrum attributed to “calorific rays” later termed infrared.


The second kind of electromagnetic radiation to be discovered was ultraviolet in 1801 by Johann Wilhelm Ritter. Based on the Herschel’s experiment and discovery, Ritter expected to find new rays beyond the violet part of the spectrum of sun light. Indeed, in an experiment similar to Herschel’s, using sunlight and a glass prism, Ritter observed the quick darkening of silver chloride preparations beyond the violet light. He attributed this to invisible chemical rays beyond the violet part of the spectrum later called ultraviolet.


Later, development of fundamental equations for the electromagnetic field by genius James Clerk Maxwell in 1862-4 provided the way to production and characterization of new kinds of waves by Heinrich Hertz (first in 1887) later termed radio waves and microwaves.


Discovery, nomenclature and characterization of X-rays are attributed to Wilhelm Röntgen who noticed fluorescence on a nearby plate of coated glass in an experiment with high voltages applied to an evacuated tube in 1895.


The last portion of the electromagnetic spectrum to be discovered was associated with radioactivity. Paul Villard in 1900 discovered a new type of radiation (after discovery of alpha and beta rays) with no charge and an especial penetrating power from radium, and after he described it, Rutherford realized it must be yet a third type of radiation and named it gamma rays in 1903. In 1914 Rutherford and Edward Andrade measured their wavelengths and found their wavelengths to be shorter than those of X-rays beside some of their similarities with X-rays.




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