Physics is very much an experimental science, but too often, students at the undergraduate level are not exposed to the reality of experimental physics ― i.e., what was done in a given experiment, why it was done, the background of physics against which the experiment was carried out and the changes in theory and knowledge that resulted. In this hook, the author helps to remedy the situation by presenting a variety of "landmark" experiments that have brought about significant alterations in our ideas about some aspect of nature. Among these scientific milestones are discoveries about the wave nature of x-rays, isotopes, the meaning of atomic number, superconductivity, fine structure in the spectrum of helium, the transistor, the neutrino, the maser and laser, higher symmetry for elementary particles and other seminal discoveries. Over 120 illustrations enhance the text, often reproductions of those published with the original experimental results. The result is a fascinating survey ideal as a supplement for intermediate or advanced undergraduate courses in experimental physics, history of science, radio and radar astronomy, crystallography, high energy physics and other disciplines.