Pairs of wires, attached to each end of the electromagnet, alternately dipped into cups of mercury, acting as terminals of an electrochemical cell. As the wires alternately moved into and out of the cups, thus making and breaking a circuit, the polarity of the electromagnet was repeatedly reversed , which produced a continuous rocking motion.
Henry was able to achieve "uniform motion, at the rate of seventy-five vibrations in a minute. In reference to the magnet's back-and-forth motion, Henry referred to this device as his " sheeps tail.
The challenge in devising an electromagnetic telegraph was not to produce continuous motion, but rather mechanical action at a great distance from a battery.
Prior to Henry's research, electrical signals could not be sent through long wires. English scientist Peter Barlow, had, in fact, speculated that the inability to transmit a signal over more than two hundred feet meant that an electromagnetic telegraph was not possible. In varying parameters while developing his powerful electromagnets, Henry had discovered that while a single pair of plates was best to send a current through several shorter wires, a trough battery of multiple plates high intensity could send a current through a very long wire.
The use of a high-intensity battery with a multiple-winding coil was essential to the development of the electromagnetic telegraph, since the losses in a long line would be relatively small. Morse learned this indirectly from Henry in , with dramatic consequences. Evidence of Henry's foundational research on the electromagnetic telegraph dates to , when he first began demonstrating to his students in Albany that a battery current could be transmitted through a thousand-foot wire.
At the far end of the wire, an energized electromagnet attracted one end of a bar magnet suspended on a pivot, which caused the other end to strike a bell. One of Henry's Albany Academy students reported seeing Henry succeed with a circuit one-and-a-half miles long. Henry continued to develop more powerful electromagnets and demonstrated to his students a way in which mechanical effects could be produced at a much longer range than previously realized.
Henry used a small "intensity" magnet in a local circuit to control a large "quantity" magnet holding up hundreds of pounds of weights.
When he energized the small magnet through a long circuit, it attracted upwards a piece of wire, which broke the local circuit and caused the weights to fall with a crash.
He did not publish a description of this primitive relay, which Morse learned of through an intermediary and which was critical in Morse's development of the telegraph, but mentioned it to Charles Wheatstone in England in and claimed to have demonstrated it to his Princeton students several years earlier.
Although Henry had no interest in pursuing commercial applications, he would later point to these demonstrations as the first to show that an electromagnetic telegraph was possible. While Samuel Morse was developing his telegraph, he sought advice and public support from Joseph Henry. In a letter that would later be cited to establish the telegraph's origin, Henry wrote to Morse in that although such an invention had been suggested "by various persons from the time of Franklin to the present," it was not "until within the last few years or since the discoveries in electro-magnetism" that it had been practicable.
Henry went on to say that "little credit can be claimed" for the telegraph's invention "since it is one which would naturally arise in the mind of almost any person familiar with the phenomena of electricity," but he supported Morse's design over the needle telegraphs being proposed by European scientists.
Three years later, the publication of a book on the telegraph by one of Morse's chief assistants, Alfred Vail, failed to credit Henry's contributions and marked the beginning of a dispute between Henry and Morse 6 that lasted many years. Henry's work with his powerful and versatile electromagnets, his motors, and telegraph circuits led him to complete important research in electromagnetism.
In the years since Oersted had reported producing a magnetic effect from a battery current, scientists had tried to produce the complementary effect: the production of electricity from magnetism. Working in England, Michael Faraday was the first to report success in November Although Henry had begun work in this area in August , at about the same time as Faraday, he encountered obstacles and delays throughout the academic year and did not begin working in earnest until June Faraday is thus credited with first achieving the effect, later termed mutual induction.
Henry's biographer, Albert Moyer, makes a compelling case, however, that Faraday was both inspired to undertake his research after reading of possible implications of Henry's work with his electromagnets and was helped considerably by learning of Henry's powerful electromagnets and his use of multiple coils. The truth is that on this particular Friday it was Charles Wheatstone who was scheduled to give a talk on his chronoscope.
Since he finished ahead of time, he filled in the remaining minutes by revealing his thoughts on the nature of light. Faraday even dared to question the existence of the luminiferous aether —a scientific heresy at that time—, which was supposed to be the medium for light propagation as so elegantly Fresnel had described in his wave theory of light.
He proposed that the light could be not the result of aether vibrations, but vibrations of the physical lines of force. Faraday tried to leave out the aether, but he kept the vibrations. In an almost apologetic tone, Faraday finishes his paper stating:. The electromagnetic waves about whose existence Faraday speculated in with his thoughts on ray vibrations , and which were mathematically predicted by Maxwell in , were finally produced in a laboratory by Hertz in The rest is history.
It is clear that Maxwell opened the door to twentieth century physics, but it is no less clear that Faraday gave Maxwell some of the keys he used. Click Enter. Login Profile. Es En. Economy Humanities Science Technology. Digital World. Multimedia OpenMind books Authors. Leading Figures. Featured author. Kristin Shrader-Frechette. Latest book.
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Oersted made the discovery for which he is famous in At the time, although most scientists thought electricity and magnetism were not related, there were some reasons to think there might be a connection.
For instance, it had long been known that a compass, when struck by lightning, could reverse polarity. Oersted had previously noted a similarity between thermal radiation and light, though he did not determine that both are electromagnetic waves. He seems to have believed that electricity and magnetism were forces radiated by all substances, and these forces might somehow interfere with each other. During a lecture demonstration, on April 21, , while setting up his apparatus, Oersted noticed that when he turned on an electric current by connecting the wire to both ends of the battery, a compass needle held nearby deflected away from magnetic north, where it normally pointed.
But it was clear to Oersted that something significant was happening. Some people have suggested that this was a totally accidental discovery, but accounts differ on whether the demonstration was designed to look for a connection between electricity and magnetism, or was intended to demonstrate something else entirely.
Whether completely accidental or at least somewhat expected, Oersted was intrigued by his observation. On July 21, , Oersted published his results in a pamphlet, which was circulated privately to physicists and scientific societies. His results were mainly qualitative, but the effect was clear—an electric current generates a magnetic force. His battery, a voltaic pile using 20 copper rectangles, probably produced an emf of about volts.
He tried various types of wires, and still found the compass needle deflected. When he reversed the current, he found the needle deflected in the opposite direction.
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