Franklin explains the action of the Leyden phial or jar. Suggests lightning-rods. Sends a kite into the clouds during a thunderstorm; through the kite-string obtains a spark of lightning which throws into divergence the loose fibres of the string, just as an ordinary electrical discharge would do.

Notices the inductive effect in one coil when the circuit in a concentric coil is completed or broken. Notices similar effects when a wire bearing a current approaches another wire or recedes from it. Rotates a galvanometer needle by an electric pulse. Induces currents in coils when the magnetism is varied in their iron or steel cores. Observes the lines of magnetic force as iron filings are magnetized. A magnetic bar moved in and out of a coil of wire excites electricity therein,—mechanical motion is converted into electricity. Generates a current by spinning a copper plate in a horizontal plane.

Improves the electro-magnet of Sturgeon by insulating its wire with silk thread, and by disposing the wire in several coils instead of one. Experiments with a large electro-magnet excited by nine distinct coils. Uses a battery so powerful that electro-magnets are produced one hundred times more energetic than those of Sturgeon. Arranges a telegraphic circuit more than a mile long and at that distance sounds a bell by means of an electro-magnet.

Forerunners at New York and Dover. Gutta-percha the indispensable insulator. Wire is used to sheathe the cables. Cyrus W. Field's project for an Atlantic cable. The first cable fails. 1858 so does the second cable 1865. A triumph of courage, 1866. The highway smoothed for successors. Lessons of the cable.

Indebted to his father's study of the vocal organs as they form sounds. Examines the Helmholtz method for the analysis and synthesis of vocal sounds. Suggests the electrical actuation of tuning-forks and the electrical transmission of their tones. Distinguishes intermittent, pulsatory and undulatory currents. Devises as his first articulating telephone a harp of steel rods thrown into vibration by electro-magnetism. Exhibits optically the vibrations of sound, using a preparation of a human ear: is struck by the efficiency of a slight aural membrane. Attaches a bit of clock spring to a piece of goldbeater's skin, speaks to it, an audible message is received at a distant and similar device. This contrivance improved is shown at the Centennial Exhibition, Philadelphia, 1876. At first the same kind of instrument transmitted and delivered, a message; soon two distinct instruments were invented for transmitting and for receiving. Extremely small magnets suffice. A single blade of grass forms a telephonic circuit.

RÖntgen indebted to the researches of Faraday, Clerk-Maxwell, Hertz, Lodge and Lenard. The human optic nerve is affected by a very small range in the waves that exist in the ether. Beyond the visible spectrum of common light are vibrations which have long been known as heat or as photographically active. Crookes in a vacuous bulb produced soft light from high tension electricity. Lenard found that rays from a Crookes' tube passed through substances opaque to common light. RÖntgen extended these experiments and used the rays photographically, taking pictures of the bones of the hand through living flesh, and so on.

What may follow upon electric induction. Telegraphy to a moving train. The Preece induction method; its limits. Marconi's system. His precursors, Hertz, Onesti, Branly and Lodge. The coherer and the vertical wire form the essence of the apparatus. Wireless telegraphy at sea.

Electricity does all that fire ever did, does it better, and performs uncounted services impossible to flame. Its mastery means as great a forward stride as the subjugation of fire. A minor invention or discovery simply adds to human resources: a supreme conquest as of flame or electricity, is a multiplier and lifts art and science to a new plane. Growth is slow, flowering is rapid: progress at times is so quick of pace as virtually to become a leap. The mastery of electricity based on that of fire. Electricity vastly wider of range than heat: it is energy in its most available and desirable phase. The telegraph and the telephone contrasted with the signal fire. Electricity as the servant of mechanic and engineer. Household uses of the current. Electricity as an agent of research now examines Nature in fresh aspects. The investigator and the commercial exploiter render aid to one another. Social benefits of electricity, in telegraphy, in quick travel. The current should serve every city house.

Observes that in boring a cannon much heat is generated: the longer the boring lasts, the more heat is produced. He argues that since heat without limit may be thus produced by motion, heat must be motion.

Shall it be a system of stationary engines or locomotives? The two best practical engineers of the day are in favour of stationary engines. A test of locomotives is, however, proffered, and George Stephenson and his son, Robert, discuss how they may best build an engine to win the first prize. They adopt a steam blast to stimulate the draft of the furnace, and raise steam quickly in a boiler having twenty-five small fire-tubes of copper. The “Rocket” with a maximum speed of twenty-nine miles an hour distances its rivals. With its load of water its weight was but four and a quarter tons.