2,637 Years of Physics from Thales of Miletos to the Modern Era. Sheldon Cohen

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      Scientists continued to do work on the attractive force discovered by the Greeks (static electricity)…

      Charles Francois Dufay (1698-1739)

      was the gardener to the king of France. His restless mind moved his talents to other directions as well, and in his spare time he produced two types of electric charges when he rubbed different substances together. Working with glass, he discovered that some charged pieces would either attract or repel other charged pieces of glass. He called these two types of effects resinous and vitreous. He theorized that matter contained two fluids in a definite balance that was disturbed during the act of rubbing; each body acquiring either an excess or a deficiency of the fluids. Subsequently the terminology of resinous and vitreous for this unknown mysterious force became negative and positive. The use of the word fluid would remain for about one hundred-fifty years, or until the exact nature of this mysterious force was discovered.

      In the mid-1700s,

      Pieter van Musschenbroek (1692-1761)

      a Dutch physicist from the University of Leyden, developed a means of storing static electricity. He half-filled a glass container with water and sealed the top with a cork. He then pierced the cork with a nail that extended into the water. The exposed nail subjected to friction caused static electricity to be stored within the glass container. Discontinuing the friction, and touching the exposed nail, resulted in a shock. This was the earliest form of what would be known as the…

      Leyden jar.

      which eventually consisted of a jar coated inside and out with tin foil. The outer tin foil connected to the earth; the inner tin foil connected to a brass rod projecting through the mouth of the jar. Charging one of the tin foils with an electrostatic machine would produce a severe shock if both tin foils were touched at the same time.

       It was possible to force a large amount of electric charge into the Leyden jar. In fact, if the jar carried a sufficiently large amount, even approaching a nearby object could discharge it and a spark would force its way through the air to the other object. When it did this, there were those who saw a resemblance to lightening. From this primitive beginning, natural philosophers developed numerous devices that created electric current.

      Benjamin Franklin (1706-1790)

      the great American politician, statesman, inventor, and natural philosopher, used a metal conductor to discharge the inner and outer layers of tin foil in a Leyden jar creating the clearly visible and audible spark. He was one of those who speculated about the similarity of the visible and audible spark to lightening. Could lightening be an electric discharge similar to the spark produced within the Leyden jar?

       To prove this hypothesis he flew a kite with a metal tip in a thunderstorm. He used wet hemp line, a conductor of electricity, to fly the kite and attached a metal key to the end of the line. From the key he attached a non-conducting silk line that he held in his hand. When he held his other hand near the key he drew sparks from it, thus proving that lightening was an electrical phenomenon with the same properties as the electric spark produced with the Leyden jar. Franklin was fortunate: the next two men who tried duplicating Franklin’s experiments died of electric shock.

       The lightening experiments brought great fame to Franklin. Much of his success as a diplomat in France was due to his reputation as a natural philosopher. For the French knew that they were receiving one of the world’s leading scientific figures, and not just an American patriot.

       Franklin showed that the electrical experiments performed in a laboratory are related to the natural events of our world---lightening. Therefore, future natural philosophic studies of nature could not be divorced from electricity.

       Franklin postulated that electricity was a single fluid that existed in all matter and explained the effects of electricity by a shortage or excess of this fluid. The word fluid, used by natural philosophers, was the primitive description of a force of nature that future experimenters would gradually shed light upon…

      Luigi Galvani (1737-1798),

      an Italian anatomist and physician discovered that when the lower legs of a dissected frog were in proximity to an electrical source, such as a Leyden jar, the frog’s muscles twitched into what he described as a “convulsive state.” Galvani had uncovered an interesting phenomenon. Whereas a spark could touch a muscle and cause it to contract, Galvani demonstrated that the muscle would contract merely by being in the proximity of an electric source. Up to this point, an electric current was only demonstrated in an instantaneous fashion. Once an electric spark transferred its current, there was no more; no further current flowed. He also demonstrated that by drawing a spark from an electrical machine at a distance from a muscle, and simultaneously touching metal to the frog’s sciatic nerve, the leg muscles twitched as if cramped. Further, he showed that touching a muscle with two different metals caused the muscle to twitch and the twitching would continue multiple times. Clearly, these muscles were being affected by electricity, but in this case the electricity would manifest itself not as one instantaneous jolt and then no more, but rather in a continuous fashion. How could this be? Galvani concluded that it was the muscle itself that generated the electric current responsible for this continuous twitching, and therefore animals utilized electricity as part of their physiological processes. He named this “animal electricity,” and thought that this was a different force than the natural electricity of lightening or the static electricity produced within the Leyden jar. The phenomenon of electricity was expanding in many directions.

       These experiments demonstrated the electrical nature of nerve muscle function and opened the door to the study of neurophysiology.

      Electrical forces in animal tissue? Did electrical energy permeate living as well as inanimate objects? Was electricity a universal force explaining life itself? These questions would “spark” much thinking and open new doors.

      Alessandro Volta (1745-1827)

      from Como, Italy was a student of languages and had a broad liberal arts education. Electricity became his hobby and he developed the battery in 1793. Rather than accept Galvani’s notion of the muscle source for the continuous electricity, he suspected that the two dissimilar strips of metal were really the electrical generating medium. Following this hunch, he discovered that electricity was produced when two different metal strips were placed within a salt solution that had no connection with animal tissue. This simple act would produce electricity that continued as long as the chemical reaction continued. The electricity was then drawn off continuously through a wire. For the first time electricity was produced by chemical means. This was a far more powerful force that could be obtained by electrostatic machines and resulted in enhanced research efforts.

       In honor of Volta’s brilliant work, the volt now describes the unit of electrostatic potential.

      It was shortly after Volta’s discovery that

      William Nicholson (1753-1815) working together with

      Anthony Carlisle (1768-1840),

      both from England, passed an electric current through water and discovered that they could break down the water into their component parts: hydrogen and oxygen. For the first time an electric current brought about a chemical reaction. They named the process hydrolysis---taking apart by electricity. Electrical insight was СКАЧАТЬ