In the beginning of the following year, 1666, when Newton was twenty-four, he purchased a prism, in order to make some experiments on Descartes' theory of colors. He made a hole in his window shutter, darkened the room, and admitted a ray of the sunlight. On the opposite wall he saw the solar or prismatic spectrum, an elongated image of the sun, about five times as long as it was broad, and consisting of _seven_ different colors; red, orange, yellow, green, blue, indigo, and violet. White light was thus discovered to be of a compound nature; a mixture of all the colors. He said, "Whiteness is the usual color of light; for light is a confused aggregate of rays endued with all sorts of colors, as they are promiscuously darted from the various parts of luminous bodies." If any one color predominates, the light will incline to that color, as the yellow flame of a candle. Heretofore, there had been all sorts of conjectures about the nature and origin of colors. Descartes believed them to be a modification of light, depending on the direct or rotary motion of its particles. But Newton showed by many experiments that color is a property of light, or innate in light itself. We speak of a thing as red because it reflects red, and absorbs all the other colors. The green leaf stops or absorbs the red, blue, and violet rays of the white light, and reflects and transmits only those which compose its green. He also found that the red rays are refracted or turned out of their course least of all the colors, and violet most, thereby discovering the different refrangibility of the rays of light; "a discovery which has had the most extensive applications to every branch of science, and, what is very rare in the history of inventions, one to which no other person has made the slightest claim." His beautiful experiments with rings resulted in his Scale of Colors, of great value in optical research. In 1668, when Newton was twenty-six, he constructed a small reflecting telescope, and soon a larger one, which he sent to the Royal Society; and was made a member of that body, in 1671. Two years previously he had been appointed to the Lucasian professorship of mathematics at Cambridge.