The lectures explain the electrical nature and physical causes of lightning and thunder, describe characteristic flashes and thunder-peal behavior, and compare atmospheric discharges with laboratory sparks and brush discharges. They review experiments that illuminate flash duration, brightness, and various forms such as forked, sheet, and globe lightning, and address phenomena like St. Elmo’s fire. Practical chapters analyze destructive effects on structures and life, outline principles and conditions for effective lightning conductors, and give rules for personal and property safety while warning of bad grounding and rival conductors. An appendix summarizes a contemporary scientific controversy over conductor theory, considering self-induction, experimental demonstrations, and arguments offered by several authorities.