In addition, the particular problems in the engagement of joints fascinated Leonardo, leading him on to the study of more general problems such as the transmission of power by gears and the strength of materials. He also spent long hours studying geometrical theories and reading Greek and Latin classical works. Laboriously, he translated these into his own formulas and made comments about them in his notebooks. He attended the lectures of John Argyropoulos, a Greek, who talked of the Aristotelian theories of natural history, and who had translated Aristotle’s _Physics_. The study of physics opened to Leonardo a whole new world of ideas. He experimented with cogwheels, and with the improvement of ways to lift weights. He became fascinated with the then-known laws of friction and built a bench upon which he tested various devices for the overcoming of frictional drag; he also tested the natural power of one body to set another in motion. This bench with its rollers and weights was similar in principle to the one used by the French physicist A. C. Coulomb almost three centuries later. Leonardo was indeed growing into a man of genius. Now everything from the stars to the flight of an insect occupied his thoughts. At the same time, he continued his studies of drawing and painting. Frequently he was seen in Florence following someone whose face had interested him—sometimes for the better part of the day—and then at night he would fill a page with sketches of this same person from memory. By developing his powers of observation in this way Leonardo came to rely more upon his own experiences and less upon what he was told or what he read. This brought him into frequent conflict with the astrologers, the alchemists and even the Church. The astrologers were men who told fortunes by the movements of the stars. The alchemists, with their knowledge of chemistry, pretended to be able to talk with ghosts and to tell the future. These men Leonardo held in contempt. Although he was a devoutly religious man, Leonardo objected to many attitudes of the Church which he considered outmoded and which stood in the way of scientific progress; because of these objections, he was frequently called a pagan. In this same year of 1469, Leonardo met the aging Paolo del Pozzo Toscanelli. Toscanelli was a famous physician, philosopher and mathematician who, just the previous year, had marked off on the cathedral floor the famous meridian line for determining the dates of the various Church holidays. The old man and the boy became not only the famous teacher and ardent pupil, but close friends.