It is rather surprising to find how much besides the theory of lenses Friar Bacon had succeeded in finding out in the department of optics. He taught, for instance, the principle of the aberration of light, and, still more marvelous to consider, taught that light did not travel instantaneously, but had a definite rate of motion, though this was extremely rapid. It is rather difficult to understand how he reached this conclusion, since light travels so fast that, as far as regards any observation that can be made upon earth, the diffusion is practically instantaneous. It was not for over three centuries later that Römer, the German astronomer, demonstrated the motion of light and its rate by his observations upon the moons of Jupiter at different phases of the earth's orbit, which showed that the light of these moons took a definite and quite appreciable time to reach the earth after their eclipse by the planet was over. {324} Albertus Magnus's other great pupil besides Roger Bacon was St. Thomas Aquinas. If any suspicion were still left that Thomas did not appreciate just what the significance of his teachings in physics was, when he announced that neither matter nor force could ever be reduced to nothingness, it would surely be removed by the consideration that he had been for many years in intimate relations with Albert, and that he had probably also been close to Roger Bacon. In association with such men as these, he was not likely to stumble upon truths unawares, even though they might concern physical science. St. Thomas himself has left three treatises on chemical subjects, and it is said that the first occurrence of the word amalgam can be traced to one of these treatises. Everybody was as much interested then, as we are at the present time, in the transformation of metals and mercury with its silvery sheen; its facility to enter into metallic combinations of all kinds, and its elusive ways, naturally made it the center of scientific interest quite as radium is at the present moment.