Made in London in the early twentieth century, this brass prism spectroscope made by John Browning, was used to separate light into its various wavelengths, which appear as different colors. Because each wavelength of light has a different index of refraction, these different wavelengths disperse from the prism inside the spectroscope at varying angles. Scientists, however, did not always believe that a single color of light could be broken down into its component colors. In the seventeenth century, they thought that color was a mixture of lightness and darkness, and when white light passed through a substance, it became contaminated by that material, resulting in a colorful dispersion of light.

However, in 1666, Isaac Newton, who had just graduated from Cambridge University’s Trinity College, returned to his family’s farm as The Great Plague struck London and began further investigating the relationships between light and color. He began his investigations by cutting a small hole in a window shade, letting a small beam of light through. When he placed a glass prism in the light’s path, the beam scattered into a rainbow, or spectrum, of colors, each of which refracted from the glass prism at a different angle. He then placed a second identical prism in the light’s path, which recondensed the spectrum of colors into a single beam of white light, and after repeating the experiment with multiple colors of light, he found that the second prism always condensed the light rays back into the original color. This proved that white light was not indivisible, as many believed, but composed of a spectrum of seven colors. Although his theory was initially criticized by members of the Royal Society of Science, including contemporary Robert Hooke, Newton eventually published his findings in his 1704 book Opticks. In the coming century, scientists would build off Newton’s findings to establish the wavelike behavior of light and eventually the full range of the electromagnetic spectrum. Newton's discoveries represented a significant advancement in the field of optics, paving the way for everything from the color wheel to the development of lasers.