HISTORY OF ELECTROMAGNETIC THEORY

The history of electromagnetic theory begins with ancient measures to deal with atmospheric electricity, in particular lightning.^[1]People then had little understanding of electricity, and were unable to scientifically explain the phenomena^] In the 19th century there was a unification of the history of electric theory with the history of magnetic theory. It became clear that electricity should be treated jointly with magnetism, because wherever charges are in motion electric current results and, magnetism is due to electric current. The source term for electric field is electric charge where as that for magnetic field is electric current( charges in motion). Magnetism was not fully explained until the idea of magnetic induction was developed. Electricity was not fully explained until the idea of electric charge was developed.

Ancient and classical history

The knowledge of static electricity dates back to the earliest civilizations, but for millennia it remained merely an interesting and mystifying phenomenon, without a theory to explain its behavior and often confused with magnetism. The ancients were acquainted with rather curious properties possessed by two minerals, amber (Greek: ἤλεκτρον,electron) and magnetic iron ore (Greek: Μάγνης λίθος, Magnes lithos, "the Magnesian stone, lodestone"). Amber, when rubbed, attracts light bodies; magnetic iron ore has the power of attracting iron

Based on his find of an Olmec hematite artifact in Central America, the American astronomer John Carlson has suggested that "the Olmec may have discovered and used the geomagnetic lodestone compass earlier than 1000 BC". If true, this "predates the Chinese discovery of the geomagnetic lodestone compass by more than a millennium".^] Carlson speculates that the Olmecs may have used similar artifacts as a directional device for astrological or geomantic purposes, or to orient their temples, the dwellings of the living or the interments of the dead. The earliest Chinese literature reference to magnetism lies in a 4th-century BC book called Book of the Devil Valley Master (鬼谷子): "The lodestonemakes iron come or it attracts i

Long before any knowledge of electromagnetism existed, people were aware of the effects of electricity. Lightning and other manifestations of electricity such as St. Elmo's fire were known in ancient times, but it was not understood that these phenomena had a common origin. Ancient Egyptians were aware of shocks when interacting with electric fish (such as the electric catfish) or other animals (such as electric eels). The shocks from animals were apparent to observers since pre-history by a variety of peoples that came into contact with them. Texts from 2750 BC by the ancient Egyptians referred to these fish as "thunderer of the Nile" and saw them as the "protectors" of all the other fish.^] Another possible approach to the discovery of the identity of lightning and electricity from any other source, is to be attributed to the Arabs, who before the 15th century used the same Arabic word for lightning (barq) and the electric ray

Thales of Miletus, writing at around 600 BC, noted that rubbing fur on various substances such as amber would cause them to attract specks of dust and other light objects. Thales wrote on the effect now known as static electricity. The Greeks noted that if they rubbed the amber for long enough they could even get an electric spark to jump

The electrostatic phenomena was again reported millennia later by Roman and Arabic naturalists and physicians.Several ancient writers, such as Pliny the Elder and Scribonius Largus, attested to the numbing effect of electric shocks delivered by catfish and torpedo rays. Pliny in his books writes: "The ancient Tuscans by their learning hold that there are nine gods that send forth lightning and those of eleven sorts." This was in general the early pagan idea of lightning^] The ancients held some concept that shocks could travel along conducting objects.^]Patients suffering from ailments such as gout or headache were directed to touch electric fish in the hope that the powerful jolt might cure them

A number of objects found in Iraq in 1938 dated to the early centuries AD (Sassanid Mesopotamia), called the Baghdad Battery, resembles a galvanic cell and is believed by some to have been used for electroplating. The claims are controversial because of supporting evidence and theories for the uses of the artifacts, physical evidence on the objects conducive for electrical functions,^[18]and if they were electrical in nature. As a result the nature of these objects is based on speculation, and the function of these artifacts remains in doubt

Improving the electric machine

The electric machine was subsequently improved by Francis Hauksbee, Litzendorf, and by Prof. Georg Matthias Bose, about 1750. Litzendorf, researching for Christian August Hausen, substituted a glass ball for the sulphur ball of Guericke. Bose was the first to employ the "prime conductor" in such machines, this consisting of an iron rod held in the hand of a person whose body was insulated by standing on a block of resin.Ingenhousz, during 1746, invented electric machines made of plate glass.Experiments with the electric machine were largely aided by the discovery of the property of a glass plate, when coated on both sides with tinfoil, of accumulating a charge of electricity when connected with a source of electromotive force. The electric machine was soon further improved by Andrew Gordon, a Scotsman, Professor at Erfurt, who substituted a glass cylinder in place of a glass globe; and by Giessing of Leipzig who added a "rubber" consisting of a cushion of woollen material. The collector, consisting of a series of metal points, was added to the machine by Benjamin Wilson about 1746, and in 1762, John Canton of England (also the inventor of the first pith-ball electroscope) improved the efficiency of electric machines by sprinkling an amalgam of tin over the surface of the rubber.