Helmholtz was one of the greatest scientists of the 19th century. He made fundamental contributions to physiology, optics, electrodynamics, mathematics, acoustics, and meteorology, but he is best known for formulating the mathematical law of conservation of energy. His approach was strongly empirical at a time when many scientists embraced deductions from mental concepts. He described body heat and energy, nerve conduction, and the physiology of the eye. What medical instruments did he invent? Discuss