1750 - 1774
Timelines
One of the dominant minds working during this period was Benjamin Franklin, the first American to make significant contributions to science. Also an accomplished statesman, philosopher and writer, Franklin developed a keen fascination with electricity in the 1740s, after he was given a glass tube and cloth with which to experiment. With this and an electrostatic generator he had built, the tireless tinkerer embarked on a series of experiments that led him to believe there was just one type of electricity after all, rather than the two types du Fay had theorized some years before.
Franklin reasoned that the repelling and attracting properties observed in different materials under different circumstances were due to the relative amounts of this fluid in the materials, rather than different types of fluids. He also concluded this fluid was found in everything, though it could be transferred from one thing to another.
Franklin’s research also led to his observation that electricity can’t be created, any more than it can be destroyed. Rather, loss of electricity in one body results in the gain of electricity in another. This became known as the principle of conservation of electric charge. Materials that gain a charge, according to Franklin’s theory, were positive, while those from which a charge was given were negative. It is to Franklin that we trace one of the oldest – and oddest – conventions regarding electricity: It moves from positive (the body with greater charge) to negative (the lesser-charged body).
Franklin’s most famous contribution to the field, of course, was his kite experiment. His suspicion that lightning and electricity were one and the same was proven when lightning struck his kite prior to a thunderstorm, traveled down a wet rope and caused an attached key to spark. This insight led to his invention of the lightning rod, the first practical invention to come out of the still-young field of electricity and one responsible for saving countless lives.
Franklin’s work fascinated scientists and others across America and Europe, including an English pastor named Joseph Priestley. In fact, Priestley met Franklin during one of the American’s sojourns in London and was inspired to do some experimenting of his own. Remarkably for a man with no formal scientific training, Priestley made a profound observation.
It began with an experiment during which a ball, suspended inside an electrified jar, seemed entirely unaffected by the force. The behavior brought to Priestley’s mind Sir Isaac Newton's Law of Universal Gravitation, which stated that the force of gravitational attraction between the Earth and other objects is inversely proportional to the distance separating the Earth’s center from the object’s center. This also meant that inside these objects no gravitational force was felt.
Priestley connected the dots, theorizing an inverse-square law for electrical force, an impressive intellectual leap that would soon be proven correct.
Toward the end of this period came a ground-breaking invention: Scotsman James Watt's condensing engine, a machine that would help spark, before the century had closed, the first Industrial Revolution.
1750 - 1774
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1750
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John Michell, an English geologist, publishes A Treatise on Artificial Magnets, which describes how to make strong steel magnets and gives an account of his discovery of the inverse-square law for the attractive and repulsive forces of magnets.
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1750
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Perh Vilhelm Margentin writes a letter to the Swedish Academy of Sciences in which he comments on the effect of the aurora borealis on a magnetized needle.
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1751
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Benjamin Franklin's letters to a colleague are published as Experiments and Observations on Electricity. The work includes Franklin’s views on positive and negative charges, the use of pointed conductors, improvements to the Leyden jar and a detailed plan for his famous kite experiment.
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1752
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The connection between lightning and electricity is proven when Benjamin Franklin’s plan to collect the charge from a storm cloud into a Leyden jar with a key attached to a kite is successfully completed.
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1759
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Franz Aepinus, a German natural philosopher, publishes his Tentamen Theoriae Electricitatis et Magnetismi (“An Attempt at a Theory of Electricity and Magnetism”), the first book to consider electricity and magnetism in terms of mathematics.
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1762
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Johann Sulzer, a Swiss physicist living in Berlin, conceives and carries out an experiment that involves placing two dissimilar metals in his mouth so that they touch one another, producing a strange sensation in the tongue. This was essentially the first tongue test of a battery, and was repeated by many other scientists, including Alessandro Volta.
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1764
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Swedish physicist Johannes Wilcke invents a simple apparatus for producing substantial amounts of electric charge, which would later come to be known as the electrophorus.
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1767
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Joseph Priestley, an English pastor and science enthusiast, deduces that the law of force between electric charges must be the same as Newton’s inverse-square law for gravitational force. His History and Present State of Electricity is released, in which all data available in the field at the time is reviewed.
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1768
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Johannes Wilcke compiles and publishes the first magnetic inclination chart that includes measurements from around the globe.
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1769
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Scottish inventor James Watt contrives the steam condensing engine, a design he improves over the next two decades. The machine is utilized late in the following century for large-scale electricity generation.
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Next Section 1775-1799
Classroom Outreach
