Overview:
This document details the crucial period in the development of electromagnetic instrumentation, leading up to the invention of the multiplier (a precursor to the galvanometer). Despite the widespread use of voltaic cells since Volta’s invention of the pile in 1800, it took two decades for scientists to realize the magnetic effects of electrical circuits. This crucial discovery was made by H.C. Oersted in 1820, and it set the stage for the rapid development of electromagnetic instrumentation.
Within five months of Oersted’s publication, three individuals – Schweigger, Poggendorf, and Cumming – independently discovered the “multiplier” principle. This principle involved using a coil of wire to amplify the magnetic effects of an electrical current, and it led to the creation of the first primitive galvanometers. The document explores the contributions of each of these individuals, analyzing their different approaches to the development of the multiplier, the design of their instruments, and their understanding of the underlying principles.
Key Findings:
- The invention of the voltaic pile (battery) in 1800 significantly advanced scientific research in various fields, including chemistry, physics, and physiology.
- While scientists were aware of a potential connection between electricity and magnetism, it took 20 years for Oersted to discover the magnetic effects of an electrical circuit.
- Three individuals (Schweigger, Poggendorf, and Cumming) independently discovered the “multiplier” principle, which amplified the magnetic effects of a circuit, paving the way for the development of the galvanometer.
- While Schweigger’s initial discovery is credited with absolute priority, Poggendorf and Cumming contributed significantly to the understanding and refinement of the multiplier concept.
Learning:
- Electrostatic Instruments before 1800:
- Electrostatic instruments relied on phenomena like attraction, repulsion, sparks, and even the sensation of electric shock to detect and measure electrical quantities.
- The goldleaf electroscope, attributed to Abraham Bennet in 1787, was a significant advancement in electrostatic instrumentation.
- The twitching of a dissected frog’s legs, observed by Galvani in 1786, served as a sensitive detector of electrical effects, although its interpretation was initially flawed.
- Instrumenting Voltaic Electricity (1800-1820):
- Volta’s invention of the voltaic pile (battery) provided a continuous source of electricity, enabling new experiments in various fields.
- While electrochemical reactions were observed, their quantitative understanding wasn’t established until Faraday’s work in the 1830s.
- The heating effect of electricity was widely observed, but it was mainly used qualitatively, for instance, in Wollaston’s platinum wire method for comparing cell strengths.
- Oersted’s Discovery (1820):
- Oersted discovered the magnetic effects of a voltaic circuit, revealing a fundamental relationship between electricity and magnetism.
- He used a compass needle to detect the magnetic field generated by an electrical current.
- Oersted’s discovery marked a turning point in electrical instrumentation, leading to the development of instruments based on electromagnetic principles.
- The Beginnings of Electromagnetic Instrumentation:
- The simple juxtaposition of a compass needle near a voltaic circuit formed the basis of the first electromagnetic instrument, later named the “galvanometer” by Ampère.
- The “multiplier” principle, independently discovered by Schweigger, Poggendorf, and Cumming, amplified the magnetic effects of a circuit by winding wire in coils around the compass needle.
- The multiplier enabled scientists to detect and measure electrical currents with greater sensitivity.
- Schweigger’s Multiplier:
- Schweigger was the first to publicly describe the “multiplier” concept and its construction.
- He focused on detecting rather than measuring electrical effects and experimented with various coil configurations.
- Poggendorf’s Magnetic Condenser:
- Poggendorf developed a more sophisticated multiplier, later called the “magnetic condenser.”
- He emphasized the importance of the number of turns in the coil and its influence on the sensitivity of the instrument.
- He also investigated the effect of wire size, cell voltage, and resistance on the instrument’s performance.
- Cumming’s Galvanometer and Galvanoscope:
- Cumming designed a straight-wire “galvanometer” that allowed for quantitative measurement of electrical currents.
- He also developed a multiple-loop “galvanoscope” for detecting electrical currents.
- Cumming introduced the concept of neutralizing the earth’s magnetic field to enhance the sensitivity of the multiplier in low-resistance circuits.
Facts:
- Volta’s pile (battery) was the first continuous source of electricity. Volta invented the pile in 1800, which consisted of stacked discs of copper, zinc, and moistened pasteboard. This device was capable of generating a continuous electric current.
- The first electrolysis of water was achieved in 1800 by Nicholson and Carlisle. They noticed gas bubbles forming on a wire in contact with water, identifying the decomposition of water into hydrogen and oxygen.
- Wollaston’s invention of “Wollaston wire” in the early 1800s enabled the precise comparison of voltaic cell strengths. This very thin platinum wire allowed for a visual comparison of the heating effect of different cells based on the length of wire they could melt.
- Oersted discovered the magnetic effects of a voltaic circuit in 1820. This discovery established a direct link between electricity and magnetism.
- Oersted’s initial publication of his discovery was a four-page pamphlet privately printed and distributed to various scientific societies and individuals. This unconventional method highlights the significance Oersted attributed to his findings.
- The term “galvanometer” was first used by Ampère in 1820 to describe the simple juxtaposition of a compass needle near a voltaic circuit. This simple setup was the first device to detect the magnetic effects of an electrical current.
- Schweigger was the first to publicly describe the “multiplier” concept in 1820. He realized that wrapping a wire coil around a compass needle could amplify the magnetic effect, making electrical currents easier to detect.
- Poggendorf’s “magnetic condenser” was a more advanced multiplier, featuring multiple turns of fine wire around the compass needle. This design significantly enhanced the sensitivity of the instrument, allowing for more accurate measurements of electrical currents.
- Poggendorf’s experiments with his “magnetic condenser” revealed that the deflection of the compass needle was not directly proportional to the magnetic force. This led him to conclude that the amplifier’s power had a maximum value depending on factors like wire size and plate area.
- Cumming used a straight-wire “galvanometer” to measure the strength of electrical currents. His instrument employed a calibrated board that could be moved vertically to achieve a standard deflection of the compass needle.
- Cumming’s “galvanoscope” used multiple loops of wire around the compass needle to detect even weaker electrical currents. This instrument was more sensitive than the straight-wire “galvanometer.”
- Cumming was the first to use the astatic principle to enhance the sensitivity of the multiplier in low-resistance circuits. This method involved neutralizing the earth’s magnetic field at the compass needle’s location.
- Cumming discovered galvanic effects in circuits using electrodes made of copper and zinc with several acids previously thought to be non-galvanic. This highlights the versatility of his multiplier instrument.
- Cumming’s experiments on the length of connecting wires suggested the inverse relationship between deflection and wire length. This observation points towards an early understanding of Ohm’s law, which wasn’t published until 1826.
- The early multiplier instruments were primarily focused on detecting electrical currents. Their quantitative measurement capabilities were still limited due to the lack of a clear understanding of the relationship between current and magnetic field.
- Poggendorf introduced the term “semi-conductor” to describe materials that exhibited partial conductivity. He observed needle deflections in circuits containing materials like graphite, manganese dioxide, and sulfur compounds, previously considered insulators.
- The multiplier principle led to the development of the galvanometer, which became the primary electrical measuring instrument. This instrument allowed for precise measurement of electrical currents and became indispensable in various fields, including physics, chemistry, and engineering.
- Early versions of the multiplier, especially Schweigger’s, were less sophisticated than later designs. Schweigger’s experiments lacked the rigor and depth of those conducted by Poggendorf and Cumming.
- The development of the multiplier was a collaborative effort. While Schweigger’s discovery is credited with priority, the combined efforts of all three individuals significantly advanced the understanding and application of electromagnetic principles in instrumentation.
- The development of the multiplier and galvanometer marked a pivotal shift in electrical instrumentation. It ushered in a new era of precise measurement and contributed to the advancement of various fields, leading to further discoveries and technological advancements.
Statistics:
- Volta’s pile could be built with up to 60 pairs of copper and zinc discs. This indicates the scale of Volta’s experiments and the potential for generating significant electrical current.
- Volta’s pile could produce sparks and shocks. This demonstrates the power of his invention and its ability to generate noticeable electrical effects.
- Volta’s pile could stimulate the senses of sight, taste, and hearing when electrodes were applied to the appropriate body parts. This demonstrates the diverse range of effects that could be achieved with Volta’s invention.
- Wollaston managed to produce platinum wire as fine as a few millionths of an inch in diameter. This highlights the incredible precision of Wollaston’s techniques and the remarkable thinness of the wire produced.
- Oersted’s voltaic apparatus was strong enough to heat a metallic wire red hot. This indicates the strength of the electrical currents used in Oersted’s experiments.
- Poggendorf’s “magnetic condenser” typically consisted of 40 to 50 turns of silk-covered copper wire. This emphasizes the importance of multiple turns in enhancing the magnetic effect and the sensitivity of the instrument.
- Poggendorf’s “magnetic condenser” had an elliptical opening with an inside clearance of about 2 lines for the compass needle. This provides a specific dimension for the instrument’s construction and the space available for the compass needle to move.
- Poggendorf used three separate circuits, each containing an 8-turn condenser, to investigate the effect of multiple turns on the deflection of the compass needle. This demonstrates the meticulous nature of his experiments and his commitment to understanding the multiplier principle.
- Poggendorf’s experiments with 13 identical coils, each with 100 turns, showed that the deflection of the compass needle increased with the number of turns but eventually reached a maximum. This highlights the saturation effect of the multiplier and the importance of optimizing the number of turns.
- Poggendorf’s experiments with coils made of wire with 1/8-line diameter produced deflections of 65 degrees even with a relatively low number of turns. This suggests that thicker wire could significantly enhance the magnetic effect and increase the sensitivity of the multiplier.
- Cumming’s “galvanometer” used a board carrying two mercury cups that could be moved vertically to achieve a standard deflection of the compass needle. This provides a specific design feature of his instrument and illustrates how he calibrated it for quantitative measurements.
- Cumming discovered that the tangent of the deviation of the compass needle varied inversely as the distance of the connecting wire from the needle. This highlights the quantitative relationship between current and magnetic field, which was later formalized in Biot-Savart’s law.
- Cumming’s “galvanoscope” was so sensitive that it could detect galvanic effects with potassium-mercury amalgam as the negative electrode and zinc as the positive electrode. This demonstrates the exceptional sensitivity of his instrument and its ability to detect previously unknown galvanic phenomena.
- Cumming’s experiments on the length of the connecting wire showed that the deflection of the multiplier needle was nearly reciprocal to the wire length. This observation points towards an early understanding of the concept of resistance in electrical circuits.
- Oersted’s instrument, described as “differing in only minor particulars from that of M. Schweigger,” was significantly simpler and less sophisticated than Poggendorf’s “magnetic condenser.” This highlights the vast difference in the level of sophistication between Schweigger’s initial discovery and later developments.
- The “Galvano-Magnetic Condenser” described in the Edinburgh Philosophical Journal of 1821, based on a verbal description, incorrectly illustrated Poggendorf’s instrument. This emphasizes the importance of accuracy in reporting scientific discoveries and the potential for misinterpretation in the absence of detailed descriptions and illustrations.
- Cumming’s early papers were considered “landmarks in electromagnetism and thermoelectricity.” This highlights the significant contributions of Cumming, despite his unassuming nature and uncertain health, to the development of these fields.
Terms:
- Electrostatic Instruments: Devices that utilize the electrostatic forces of attraction and repulsion to detect and measure electrical quantities.
- Electrostatic Machine: A device that generates static electricity by friction.
- Leyden Jar: An early form of capacitor used to store static electricity.
- Voltaic Pile: The first battery, invented by Alessandro Volta in 1800, consisting of stacked discs of copper, zinc, and moistened pasteboard.
- Crown of Cups: A voltaic cell arrangement, also invented by Volta, consisting of separate copper and zinc plates in salt water solutions connected in series.
- Electrolysis: The decomposition of a chemical compound by the passage of an electric current.
- Galvanism: The flow of electric current through a circuit containing an electrolyte, particularly in biological systems.
- Multiplier: A device, the precursor to the galvanometer, that amplifies the magnetic effects of an electrical current by winding wire in coils around a compass needle.
- Galvanometer: An instrument used to detect and measure electrical currents based on the principle of electromagnetic induction.
- Astatic Principle: A technique used to enhance the sensitivity of magnetic instruments by neutralizing the earth’s magnetic field at the compass needle’s location.
Examples:
- Galvani’s observation of frog leg twitching: Galvani discovered that the legs of a dissected frog would twitch when exposed to discharges from an electrostatic machine. This observation, though misinterpreted initially, provided crucial evidence of the electrical nature of animal tissues.
- Nicholson and Carlisle’s electrolysis of water: These researchers accidentally observed the decomposition of water into hydrogen and oxygen when they used a voltaic pile to pass an electric current through water. This discovery contributed significantly to the understanding of electrochemical reactions.
- Wollaston’s production of “Wollaston wire”: Wollaston’s technique for producing exceptionally thin platinum wire provided a tool for comparing the strength of voltaic cells by visually observing the length of wire they could melt.
- Oersted’s discovery of the magnetic effects of a voltaic circuit: Oersted’s observation that a compass needle deflected when placed near a wire carrying an electrical current provided the foundation for electromagnetic instrumentation.
- Schweigger’s “doubling apparatus”: This simple device involved winding two wires around a compass needle, one above and one below, to amplify the magnetic effect. This was Schweigger’s initial exploration of the multiplier principle.
- Poggendorf’s “magnetic condenser”: Poggendorf’s design involved multiple turns of fine wire wrapped around the compass needle, significantly enhancing the sensitivity of the instrument and enabling more accurate measurements.
- Cumming’s “galvanometer”: Cumming’s instrument used a straight-wire loop and a calibrated board that could be moved vertically to measure the strength of electrical currents.
- Cumming’s “galvanoscope”: Cumming’s device employed multiple loops of wire around the compass needle to detect very weak electrical currents, demonstrating its superior sensitivity.
- Cumming’s use of the astatic principle: Cumming neutralized the earth’s magnetic field at the compass needle’s location to further enhance the sensitivity of his instrument, especially in low-resistance circuits.
- Poggendorf’s experiments with “semi-conductors”: Poggendorf observed needle deflections in circuits containing materials like graphite, manganese dioxide, and sulfur compounds, challenging the traditional notion of insulators and introducing the concept of “semi-conductors.”
Conclusion:
The early development of electromagnetic instruments, particularly the multiplier, was a fascinating period characterized by independent discoveries, collaborative efforts, and a gradual shift in understanding from qualitative observation to quantitative measurement. The invention of the voltaic pile provided the impetus for a wave of experimental discoveries, leading to the critical realization of the magnetic effects of electrical circuits by Oersted. The multiplier, independently discovered by Schweigger, Poggendorf, and Cumming, transformed electrical instrumentation, paving the way for the development of the galvanometer and ultimately revolutionizing the study and application of electricity and magnetism. Although Schweigger’s initial discovery holds a place of honor, it was the combined efforts of all three individuals that truly propelled the development of this vital instrument and contributed significantly to the advancement of science and technology.