Grimaldi observed curious diffraction fringes produced by a narrow slit. Surprised by the observation, he concluded that light had to consist of a very fine fluid of some sort in a state of constant vibration.
Huygens proposed his wave propagation theory which would get the ball rolling for future research. All the while, Sir Isaac Newton had also gotten his feet wet with diffraction
His studies culminated in the publishing of his book, Optiks
The first discovery of electromagnetic radiation other than visible light.William Herschel discovered infrared radiation.
Electromagnetic radiation had been first linked to electromagnetism.
James Maxwell developed four partial differential equations for the electromagnetic field. Two of these equations predicted the possibility of, and Behavior of, waves in the field. Analyzing the speed of these theoretical waves, Maxwell realized that they must travel at a speed that was about the known speed of light.
Physicist Heinrich Hertz built an apparatus to generate and detect what are now called radio waves. Hertz found the waves and was able to infer (by measuring their wavelength and multiplying it by their frequency) that they traveled at the speed of light. Hertz also demonstrated that the new radiation could be both reflected and refracted by various dielectric media, in the same manner as light. For example, Hertz was able to focus the waves using a lens made of tree resin. In a later experiment, Hertz similarly produced and measured the properties of microwaves. These new types of waves paved the way for inventions such as the wireless telegraph and the radio.
Wilhelm Röntgen noticed a new type of radiation emitted during an experiment with an evacuated tube subjected to a high voltage. He called these radiations x-rays and found that they were able to travel through parts of the human body but were reflected or stopped by denser matter such as bones. Before long, many uses were found for them in the field of medicine.
Paul Villard was studying the radioactive emissions of radium when he identified a new type of radiation that he first thought consisted of particles similar to known alpha and beta particles, but with the power of being far more penetrating than either.
He realized that they were fundamentally different from charged alpha and beta particles and Edward Andrade measured their wavelengths, and found that gamma rays were similar to X-rays, but with shorter wavelengths and higher frequencies.
British physicist William Henry Bragg demonstrated that gamma rays are electromagnetic radiation, not particles.
Ernest Rutherford, had named them gamma rays.