A D V E N T U R E S in C Y B E R S O U N DInvestigations with Electricity and Magnetism : 1732 - 1856Until the 19th century, electricity and magnetism were considered more likely living forces than purely physical phenomena. Luigi Galvani (1737-1798) and Alessandro Volta (1745-1827) were both working on the biological problems of sensibility and irritability in the 1790s. Prior to 1800, all experiments with electricity were done with static electricity. Volta's invention of the Couronne des tasses (crown of glasses) and the voltaic pile were key events in the history of electrical studies and in the history of chemistry. The couronne des tasses was a battery, as was the voltaic pile plates of metal (zinc and copper) separated by brine or brine soaked cardboard with wires running from the two end poles (the end pieces of zinc and copper). A voltaic pile, or battery, produces a steady and measurable electrical current on demand. This ability to produce a steady current is the key to basic experimentation with electricity. Experiments with electricity and magnetism between 1785 and about 1830 served as the basis for James Clerk Maxwell's later mathematical calculations and predictions that would create Field Physics in the second half of the 19th century. Field Physics is the branch of physics dealing with electromagnetic radiation. Maxwell's equations "predicted" the existence of radio waves, x-rays, ultraviolet light, etc.
1732 Stephen Gray (England) demonstrated electrical conductivity by stringing wires through the trees in an orchard. Passed static electricity through the wire. 1745 The Leyden Jar is invented in Leyden (Netherlands). The first electrical condenser, a storage mechanism for an electrical charge. The first Leyden jars were a lierally a glass jar filled with water and two wires suspended in the water. Later, the water was replaced with metal foils wrapped so that there was insulation between the layers of foil, the two wires were attached to the ends of the sheets of foil. When one wire was attached to the ground, the 'Leyden Jar' accumulated static electricity. Connecting the second wire to ground, will give a single 'zap', often a spark. 1746-52 Ben Franklin flying kites in Pennsylvania to demonstrate that lightning is a form of static electricity. (Wire run to the kite could produce sparks at the ground, or charge a Leyden Jar.) Led Franklin to invent the lightning rod and to formulate the single fluid (imponderable fluid) theory of electricity. Previous theories had held there were two electrical fluids and two magnetic fluids. Franklin theorized just one imponderable electrical fluid (a fluid under conservation) in the universe. The difference in electrical charges was explained by an excess (+) or defect (-) of the single electrical fluid. This is where the positive (+) and negative (-) symbols come from in electrical science. Debates over the two fluid vs. single fluid theories were hot and heavy for many years, but gradually Franklin's single fluid theory came to predominate. 1785 Charles Augustus Coulomb (1736-1806) invented the torsion balance, thus performing the first quantitative experiments in the history of electrical science. The torsion balance is a simple device: a horizontal cross-bar is mounted on a stretched wire. A ball is then mounted on each end of the cross bar. Given a positive or negative charge, those balls will then attract or repel other objects that carry charges. The balls responding to these charges will try to twist the wire holding the cross bar. The wire resists twisting, and how much twisting occurs tells you how much force the attraction (or repulsion) exerted. Coulomb showed electrical attractions and repulsions follow an inverse square law, i.e., whatever the attraction or repulsion when two objects are brought into contact, the strength of the force will be only proportional to 1/d2 for any distances that separate them. For example, whatever the attraction or repulsion at 1 inch of separation, the attraction or repulsion will be 1/4 of that at 2 inches, 1/16 at 4 inches, 1/25 at 5 inches, etc. 1791 Luigi Galvani (1737-1798) investigating electricity as the source of life. Galvani believed living tissues contained electricity. He conducts a number of experiments including the connecting of pieces of metal (zinc, copper, iron, tin, etc.) to a piece of wire, zinc and copper worked really well, to create what's called a bimetallic arc. Galvani held one end of this bimetallic arc in his mouth. He touched the other end to the wet area in the corner of his eye and saw a brilliant flash of light. In what is considered to be his most famous experiment, Galvani attached one end of a bimetallic arc to the muscle (and the other to the right crural nerve) of a severed frog's leg, causing the frog's leg to kick violently. Galvani believed the electricity that caused the frogleg to "kick" was in the leg. He thought the bimetallic arc simply allowed it to pass. That conclusion bothered Alessandro Volta. 1800 Alessandro Volta (1745-1827) announced the results of his experiments investigation Galvani's claims about the source of electricity in the frogleg experiment. He undertook to prove that he could produce electricity without the frog. Took the same bimetallic arcs (several of them) and dipped them in glasses of brine. This was Volta's Couronne des Tasses, his first battery. His voltaic pile was another (new, improved configuration for a battery) With it he showed that the bimetallic arcs (not Galvani's froglegs) were the source of electricity. Effectively, this experiment marked the end of the biological search for electricity as the life force because Volta showed the electricity came from entirely inorganic materials. At the same time Volta's pile brought biological interest in electricity to an end, it created new interests in the phenomenon among both physicists and chemists. For physicists, the availability of a steady current offered the first opportunity for systematic experimentation with electrical phenomena. 1820 Hans Christian Oersted (1777-1851) in Denmark demonstrated a relationship between electricity and magnetism by showing that an electrical wire carrying a current will deflect a magnetic needle. 1820 François Arago (1786-1853) in France showed that a spiral of copper wire carrying a current will attract iron filings thus creating the first electromagnet. 1822-27 André Marie Ampère (1775-1836) gave algebraic expression to the basic attractions, repulsions, etc., formalizing understanding of relationships between electricity and magnetism. 1826 Georg Simon Ohm (1787-1854) announced Ohm's Law (used to describe the resistance in conducting materials). Ohm wanted to measure the motive force of electrical currents (the electroscopic force as he called it). He found that some conductors worked better than others and quantified the differences. 1820s Michael Faraday (1791-1867) surmised that an electrical current moving through a wire creates "fields of force" surrounding the wire. He believed that as these "fields of force" were established and collapsed, they could move a magnet. This led to a number of experiments with electricity as a motive (moving) force 1821 Faraday built the first electric motor, a device for transforming an electrical current into rotary motion 1831 Faraday made the first transformer, a device for inducing an electrical current in a wire not connected to an electrical source. On breaking the circuit with a "key", the flux in the fields of magnetic force in the battery side of the winding on the iron ring "induces" a current on the non-battery side. 1856 Most did not believe in Faraday's lines of force (they violate the idea of an imponderable fluid), but James Clerk Maxwell in 1856 wrote a mathematical treatise formalizing the theory: On Faraday's Lines of Force. At that point, we can say the imponderable fluid theory of electricity was dead. Maxwell's work marks the start of a new area, field physics.
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