Color reflected color depends upon the viewing angle. Numerous scientists have carried out research in butterfly wings and beetle shells, including Isaac Newton and Robert Hooke. Since 1942, electron micrography has been used, advancing the development of products that exploit structural color, such as "photonic" cosmetics. Color Color (American English), or colour (Commonwealth English), is the characteristic of human visual perception described through color "categories", with names such as red, orange, yellow, green, blue, or purple. This perception of color derives from the stimulation of cone cells in the human eye by electromagnetic radiation in the visible spectrum. Color categories and
Moving walkway the book, the fast lane stops while the second lane keeps running at ). In the Wells and Asimov works there are more steps in the speed scale and the speeds are less extreme. In Arthur C. Clarke's novel, "Against the Fall of Night" (later rewritten as "The City and the Stars") the Megacity of Diaspar is interwoven with "moving ways" which, unlike Heinlein's conveyor belts, are solid floors that can mysteriously move as a fluid. In the novel, Clarke writes, In his non-fiction book "Profiles of the Future", Arthur C. Clarke mentions moving sidewalks but made of some sort