This is my summary of the inventions I learned about in lessons thirty-six through thirty-nine. In lesson thirty-six, I learned about the invention of the electromechanical relay. Joseph Henry was fascinated by the earth’s magnetic field, and improved the electromagnet. He built on that to invent the electromechanical relay. The electrical relay uses an electromagnet to drive either a mechanical or an electrical switch. The electromagnet is activated when a current passes through the wire coiled around the magnetic cord, and the magnet pulls in an armature. The armature causes a metal contact to move, which either opens or closes the circuit.

Lesson thirty-seven was about the invention of the revolver. Samuel Colt invented the revolver, which was inspired by the action of the steering wheel on ships. Samuel Colt was expelled from school after setting it on fire with explosives, so his father sent him to the sea to learn the sailing trade. That was how Colt was inspired to apply the steering wheel action of ships to handguns. The revolver can accurately and reliably fire six shots in rapid succession, as well as pack a powerful punch.

In lesson thirty-eight, I studied the invention of Morse code. Samuel Morse, the inventor of Morse code, was the son of a Calvinist preacher named Jedidiah Morse. Samuel Morse was far away painting for a French man when he got a letter from his father saying his wife had suddenly died. This inspired Morse to improve ways to communicate over long distances so news could travel much quicker. Morse code is similar to Braille, and encodes the alphabet in a series of dots and dashes.

Last of all, in lesson thirty-nine, I learned about the invention of the circuit breaker. Charles Grafton Page was interested by electricity as a child, which led him to invent the circuit breaker around the year 1836. Circuit breakers interrupt electrical faults before they can cause too much physical damage, such as fire. Circuit breakers protect electric cables in the circuits they supply, and break the flow of electricity during an electrical fault before the fault causes damage.