Time traveler spotted! This textbook claims to be from January 1st, 1900—a full 25 years before Heisenberg, Schrödinger, and Born formalized quantum mechanics! Either John S. Townsend mastered both quantum physics AND time travel, or Amazon's metadata is experiencing its own uncertainty principle. For reference, in 1900, Planck had barely introduced the quantum concept, and Einstein's photoelectric effect paper was still 5 years away. This is like finding a book on smartphone repair written during the Spanish-American War. 64 reviewers giving it 4.5 stars though—clearly they appreciate the classics!