Although he mainly concentrated on classical mechanics and the principles of geometric optics, Isaac Newton (1642–1727) did make several important discoveries in the field of sound. His major contribution was his work on sound wave propagation. He showed that the velocity of sound through any medium depended upon the characteristics of that particular medium. Specifically, Newton demonstrated that the elasticity and the density of the medium determined how fast a sound wave would travel. Because Newton worked before the field of thermal physics was developed, his theory has errors, but they are not significant to the calculation of sound speed.