A photoelectric alarm and a "Photophone" (for transmitting music/speech via light beams). Telephone amplifiers and public address systems.
Modern textbooks are dense with calculus and complex math. Morgan uses diagrams and "try it and see" pedagogy. He explains why a capacitor blocks DC but passes AC using water-pipe analogies, not Maxwell’s equations.
Alfred Morgan (1889–1972) was an MIT-educated engineer and inventor who held several patents for radio devices. He is best known for making complex electronic concepts accessible to young readers through his four-part "Boys' Book" series. While originally written for "boys," later editions and modern perspectives recognize these books as foundational texts for any curious mind.
Before the internet, there were books. Before Arduino tutorials, there were schematics drawn in pen and ink. Alfred Powell Morgan (1889–1972) was a professor of electrical engineering at Denison University and a prolific author. He understood that theory meant nothing without practice.