He gave a demonstration of his telescope to the Royal Society in 1671. Based on his theory of color, Newton concluded that refracting telescope lenses would be plagued by chromatic aberrations (the dispersion of light into colors) and built the first practical reflecting telescope, using reflective mirrors rather than lenses as the objective to solve that problem. When he placed a second prism upside-down in front of the first, the band of colors recombined into white sunlight, thereby proving his hypothesis that white light is made up of all the colors of the spectrum combined. Then he placed a glass prism in the sunbeam and observed the rainbow bands of light in the color spectrum. And as a young scientist at the University of Cambridge, he conducted what is known as his experimentum crucis, darkening his room one sunny day and making a hole in the window shutter to let a narrow beam of sunlight into the room. For instance, he once stuck a long sewing needle (bodkin) into his eye socket between the eye and bone and recorded the colored circles and other visual effects he saw.

Newton is justly most famous for his Principia and the co-invention of calculus, but he also had a longstanding interest in optics. Collectors and rare book dealers love a good tale of rediscovery, especially one which came to light-quite literally in this case-in the way this one did.' DiLaura has described his discovery as 'a once-in-a-collector’s-lifetime event,' and it really is. 'When DiLaura bought this copy more than 20 years ago from an English rare book dealer in West Sussex, neither buyer nor seller had any idea of its history. “It’s becoming increasingly rare for an author’s own copy of a book of this magnitude to fly under the radar for so many years,' said Pom Harrington, owner of Peter Harrington Rare Books, which is selling the tome.

Opticks 1704