This book of almost 250 puzzles begins where our first book, Mad About Physics: Braintwisters, Paradoxes, and Curiosities (2001) ended with the physics of the late nineteenth and early twenti eth centuries. The Michelson-Morley experiment of 1887, the challenges posed by atomic spectra and blackbody radiation, the unexpected discoveries of X-rays in 1895, radioactivity in 1896, and the electron…