"Young... examined the colors that are produced by scratches on a smooth surface, in particular testing the light from "Mr. Coventry's exquisite micrometers," which consist of lines scratched on glass at measured intervals. These microscopic tests brought the same results as the other experiments. The colors were produced at certain definite and measurable angles, and the theory of interference of undulations explained them perfectly, while, as Young affirmed... no other theory hitherto advanced could expIain them at all. Taking all the evidence together Young declared that he considered the argument he had set forth in favor of the undulatory theory of light to be sufficient and decisive."