Final answer:
Newton discovered that white light is composed of all the colors of the rainbow by passing it through a prism, and he concluded that this proves light is made of particles, a view that originally prevailed over the wave theory until experiments by Young and others.
Step-by-step explanation:
Newton's Prismatic Discovery
In 1672, Sir Isaac Newton demonstrated a groundbreaking experiment that changed the understanding of light. He permitted sunlight to pass through a prism, which revealed that what appears to us as white light is actually a mixture of all the colors of the rainbow. Before Newton's discovery, the prevalent belief was that the prism itself produced the colors. However, Newton's experiment showed that the prism merely separated the pre-existing colors inherent in white light. This phenomenon, known as dispersion, occurs because different colors (or wavelengths) of light are bent by different amounts as they pass through the prism, resulting in the spectrum of colors. This finding was contrary to the corpuscular theory of light that Newton himself proposed, which described light as streams of particles rather than waves. At the time, Christiaan Huygens and later scientists like Thomas Young proposed a wave theory, but it was Newton's particle theory that initially prevailed due to his stature. The acceptance of light's wave nature came after Young's double-slit experiment in 1801, which clearly showed optical interference.