From history of Electrical Engineering II: 18-th Century Electrostatic Experiments and a First Current Source Creation Alexander G. Mikerov IEEE Senior Member Control Department St.Petersburg State Electrotechnical University “LETI” 5 Prof. Popov str., St.Petersburg, 197376, Russia
[email protected] Abstract — The paper covers the electrical science development from the middle of the 18-th century to the beginning of the 19-th century. It overviews main inventions made by P. Mushenbroek (Leiden jar), B. Franklin (lightning rod), Ch. Coulomb (Coulomb’s balance), А. Volta (Volta’s cell, condenser, electrometer) and his followers. It clarified the nature of electricity, created a new electrical discipline – electrostatic and also the sound background for the following important discovery of 19-th century – electromagnetism. Index Terms — Electrostatics, Leiden jar, lightning rod, Coulomb’s balance Volta’s cell, History of electrical engineering. Fig. 1. Pieter van Musschenbroek (1692 – 1761).
I. INTRODUCTION In the previous paper [1] covering the huge period of the mankind history from Old Ages till 17-th century it was shown that original observations of an amber and magnet phenomena were supplemented by first researches of W. Gilbert, O. Guericke, Ch. Du Fay, other scientists and invention of the first electrical machine generated electrical charges. These open doors to a broad exploration of a static electricity as the first fundamental component of the electrical nature [2]. In this paper the next important component of this science is overviewed including contributions of such physics geniuses as P. Musschenbroek, B. Franklin, Ch. Coulomb, L. Galvani, A. Volta and their followers. Main static electricity laws were discovered and electrical currents were found out. That created a solid steppingstone for the next huge discovery known as an electromagnetism. II. FUNDAMENTAL ELECTROSTATIC FINDINGS In 1745 Dutch professor Pieter van Musschenbroek (Fig. 1) increased the O. Guericke’s machine power by aggregating it with a capacitor in the form of a water jar. The finding was made in Leiden University and such device was called as the “Leiden jar” shown in Fig. 2. Electric charges generated by hands rubbing the rotating Guericke’s sphere 1 flow through iron chains 2 and gun barrel 3 on silk filaments 4 charging the glass jar 5 with water. Touching the jar bottom and the barrel Musschenbroek was shocked by a powerful electrical discharge in several hundreds volts following by pictorial
electrical sparks. Such astonishing experiment spreads very quickly over enlightened Europe and became a stylish fun in fashionable parlours (Fig. 3) [3].
Fig. 2. Leiden jar.
For French king Louis’s XIV amusement a chain of 180 guardsmen touched different Leiden jar terminals and promptly jumped up with convulsion faces. Nicolay Gogol’s famous comedy “The InspectorGeneral“ concludes by phrases: “All are struck as by a thunderbolt. A cry of amazement bursts from the ladies simultaneously. The whole group suddenly shifts positions and remains standing as if petrified” [4]. Surprising phenomena was employed by travelling circus shows with vast electric performance. By chance one of such show in Philadelphia was visited by wealthy American publisher Benjamin Franklin (Fig.4).
Fig. 5. Experiment with the kite. Fig. 3. Bon ton fun.
This spectacle impressed him so much than he changed his lifestyle and became the first famous American electrical researcher. Franklin ordered different advanced electrical equipment from Europe and arranged experiments which made his name popular among leading European and American scientists.
Fig. 4. Benjamin Franklin (1706 – 1790)..
First of all he rejected the old opinion that there are two different electricity sorts “glass” and “resin” and proved that that it is only one form of very small particles, flowing through a conductor as any “electrical fluid”. “Glass” electricity means an over plus of such particles and their deficit is “resin” electricity. He voluntarily assigned the sign “+” to the over plus of electrical particles and the sign “–“ to their deficit. Electrical particles tend to flow from positive to negative terminals. Now we know that such explanation is very similar to the electron nature of electrical charges forming an electric current. However electrons are negative charged hence should flow from “-“to “+”terminals. But to honor Franklin's contribution and to avoid a confusion all following and modern textbooks in electrical engineering declare by convention that the current is flowing from the positive to negative terminals. Besides the scientific community accepts other terminology first proposed by this scientist such as: “battery”, “capacitor”, ‘conductor”, “charge”’ “discharge”, “winding” and so on. However Franklin’s major contribution was the lightning electrical nature discovery. His famous kite experiment in 1751 is shown in Fig. 5 schematically and in an older etching. The homemade kite was flown in the sky with a thunderstorm cloud and its rope was tied to a Leiden jar in hands. Rain wet the rope; it became conductive and charged the Leiden jar from the cloud.
Franklin observed electrical sparks and other effects featured for such instrument. It is obvious that he was lucky to be alive because usually the lightning potential may be several hundred millions volts. Other brave lightning experimentalists were not so lucky and for example in 1753 Russian Academician George Richmann was killed by a fireball. During the same thunderstorm experiment another Russian Academician Mikhail Lomonosov remained accidentally alive by assertion of [3] only due to his wife persistent appeals to suspend dangerous tests. The greatest Franklin’s merit was the proposal to defend high buildings from a lightning by erecting a lightning rod over them. However not all in those days supported this idea and it met some fierce objections. In famous A. Ostrovsky’s drama “The Storm” [5] mechanic Kuligin explain a thunderstorm as an electricity manifestation. Whereat the merchant Dikoy stamped: - “Lectricity he says! Ah, a brigand you are and no mistake! a storm is sent as a chastisement to make us feel our sins, and you want with rods and tackle of one sort and another, God forgive you, to ward it off! What, are you a Tartar or what? …” Amongst doubting in lightning rods was the French government too until in 1782 a catastrophic thunderstorm in Philadelphia ruined the French Consulate and killed an officer. It was the only damaging building because all other ones were equipped by B. Franklin’s lightning rods [3]. Then France capitulated too and the new invention permeated through the world very fast as the first practical electricity science application in a day to day life. Franklin is also much respected as an American successful diplomat and a coauthor of the Declaration of Independence and the USA Constitution. In Fig. 6 he is shown reading a text from this Constitution.
Fig. 6. Franklin’s statue at the University of Pennsylvania.
There are a lot of other Franklin’s monuments in USA and one of them has the table in Latin: “He seized the lightning from Heaven and the scepter from the Tyrants”[3]. His huge contribution in the science and American life is highly recognised as follows: 1. Charge unit in the CGS system is called as 1 franklin. 2. Franklin’s electrical kite is in logos of former American Institute of Electrical Engineers (AIEE) and its successor Institute of Electrical and Electronics Engineers (IEEE) as it is shown in Fig. 7.
Similar proposals were to evaluate a charge value by feel. In one of the first telegraph receiver an operator finger shorted two terminals and detected short and long pulses in the line. Such device was called as “physiological telegraph”. In 1774 Charles Coulomb invented very precise instrument for small mechanical force measurement shown in Fig. 10.
Fig. 10. Coulomb’s balance. Fig. 7. AIEE (left) and IEEE (right) logos.
3. He is the person #1 in the List of the most famous men and women in American history [6]. 4. Franklin’s portrait decorates the USA largest denomination $100 (Fig. 8).
It includes: a scale 1, an elastic string or filament 2, a beam with a charged ball 3 and a fixed charged ball 4. The elastic string or filament twists strictly proportional to the force acting between two charged balls. They repel in case of homonymous charges and attract in case of heteronymous ones. Coulomb’s balance sensitivity was developed up to 3·10-6 mgram/degree – the value didn’t achieve by any other method till now. The mail result of his experiments was the famous Coulomb’s law of interacting charges q1 and q2: fC =kCq1q2/R2,
Fig. 8. Franklin’s portrait at the USA banknote.
The next great electrical scientist was French military engineer Charles Coulomb (Fig. 9). He converted electricity to the precise science by introducing a charge measure. Before him all electrical evaluations were made visually and roughly. For example M. Lomonosov proposed to measure a charge value by an electrical sparks colour scale as following: weak blue, obviously blue, rather red, cherry-blossom and so on.
Fig. 9. Charles Coulomb (1736 – 1806).
where: fC – Coulomb’s interacting force, R – distance between charges, kC - Coulomb’s constant. Coulomb was good educated man and he turned attention to a similarity with the Newton's law of gravitation for two masses m1 and m2: fN =kNm1m2/R2, where: fN – gravitation force, R – distance between masses, kN - Newton's constant. The similarity is really surprising however till now no evident explanation for this phenomenon is found. Coulomb was memorialized in the name of a charge unit 1 coulomb in SI system. He was elected to the Paris Academy of Science in spite to his military position. Hence at the end of 18-th century the static electricity science related to motionless charges was formed and scientists focused on the electrodynamics as a new science about moving charges formed an electric current [2]. Now this name electrodynamics is associated more with the Maxwell’s electromagnetic theory. III. ELECTRODYNAMICS SCIENCE ORIGIN The first contribution to this new science was made by a man far from physics – Italian professor in anatomy from Bologna University Luigi Galvani (Fig. 11). In 1791 he published his experiments with frogs which showed that a frog cut paw twitched by connected its ends by
Fig. 11. Luigi Galvani (1737 – 1798).
Fig. 13. Alessandro Volta (1745 - 1827).
a bimetal wire (Fig. 12). Professor Galvani explained it by assuming that the frog body generates new sort of electricity called by him as an “animal electricity”. This publication initiated a huge public resonance, many inquisitives rushed to catch and prosect poor frogs and that annoyed public community very much. Galvani was labeled as a “charlatan” and the person tried to resurrect dead by “corpses galvanizing” [3].
Similar experiment is demonstrated now in the Moscow Polytechnic Museum with a simple circuit alike shown in Fig. 14 [7]. By shortening of two plates from heterogeneous metals (for example, aluminum and brass) by two hands one can see a galvanometer arrow deviation.
Fig. 14. Experiment with a man..
Such experiments pushed Volta to the idea of an electrical cell proposed him in 1800 (Fig. 15). This cell had zinc 1 and silver or copper 3 discs separated by
i Fig. 12. Experiments with frogs..
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However the history has shown that Galvany really discovered a new amazing electrical phenomenon and so his name may be found in a lot of modern terms and devices invented without his any participation such as: galvanic electricity, galvanic currents, galvanic cell, element or battery, galvanic coupling, galvanometer, galvanization and so on. Concerning Galvani’s explanation of the opened effect nobody could deny facts shown in his experiments but somebody disagreed the Galvani’s reasoning. Amongst these doubtful was another Italian professor in physics from Pavia University Alessandro Volta (Fig. 13). He was well familiar with Galvani’s experiments and proposed that the electricity was generated not by the frog body but by the bimetal conductor separated by an alkali fluid in the frog paw. To prove it Volta put one silver coin under his tongue, another over it, connected coils by a wire and perceived a slight burning similar to one acquired by our tongue shorted a battery terminals [3].
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Fig. 15. Voltaic cell.
a paper soaked with alkali 2. Several cells connected in serial formed an electrical battery acting as an electrochemical current source. Two such batteries from Pavia University Museum are shown in Fig. 16.
Fig. 16. Voltaic batteries.
Volta’s battery is similar to a Leiden jar but it generates charges permanently causing a conductor connected the battery terminals heating up to a red color (Fig. 15). Volta expected that any substance called by him as an electric “current” is flowing from the battery positive terminal to its negative ones. Other terms introduced by him were an “electro moving force (EMF)” impelling charges to flow, a ‘potential difference” or “potential” appearing between any conductor ends while a current is flowing through it and an “electric circuit” as a conjunction of all elements forming the current pass way. At first such currents were called in public as “voltaic currents” and “galvanic currents” but later only the last name survived. Electrical battery inventing by Volta is called as a “voltaic battery” or an "electric column" or pile and sometimes as a “galvanic battery”. However the electrical battery was not a single Volta’s very useful innovation. He invented a first air condenser or capacitor in a form of two metal discs separated by an air gap. To explore a relation between the condenser capacity and a potential difference across its terminals Volta proposed also new potential instrument named as an “electroscope” or “electrometer”. The experimental assembly is shown in Fig. 17. It has a metal rod 1 (upper terminal) connected with the condenser 2 and the electrometer looks like moving straws or gold petals 3 into a glass jar 4 with its bottom 5 as a down terminal. By applying a potential difference between upper and down terminals one can see straws divergence proportional to the potential value.
IV. VOLTA’S FOLLOWERS It turned out very easy and cheap to make a voltaic battery and many scientists created huge columns. One of such battery was constructed by Russian professors in physics from the Saint Petersburg Military Medical Academy Vasiliy Petrov in 1802. His battery (Fig. 18) had
Fig. 18. Petrov’s battery.
4200 zinc and copper discs with total length 12 meters. With such battery B Petrov was the first observer of an electric arc 2 between electrodes 1 and 3 as it is shown in Fig. 19. Petrov used the arc for metals melting and separating from an ore. Unfortunately his writings were not known to European scientists because Petrov didn’t master foreign languages, had no contacts with European colleagues and published all his findings in little-known Russian medical magazines.
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2
3
Fig. 19. Electric arc..
Fig. 17. Volta’s condenser and electrometer.
At first the condenser 2 was charged from a battery. Then the battery was disconnected and its charge q keeps constant. By lifting the condenser upper disc and hence decreasing its capacity C one can see an angle between straws and hence the condenser potential V increasing in accordance with the equation
For this reason the electric arc discovery was usually associated with famous English scientist Humphry Davy demonstrated it only in 1808 [8] Professor Petrov’s authentic portrait is not preserved and his only commemoration is a memorable plague at the wall of the Saint Petersburg Military Medical Academy. Other findings were made by applying voltaic battery to a liquid catholysis. In 1800 English chemists William Nicholson and Anthony Carlisle in an experiment shown in Fig. 20 decomposed water into oxygen and hydrogen.
q = CV = const, Volta’s achievements and contributions were commemorated as following: Potential difference is called as a “voltage” and its value in the SI system is measured in volts. Voltage instrument name is a “voltmeter”. Even an electric arc has the name a “voltaic arc” while Volta had no relation to its invention.
Fig. 20. Water decomposition.
Humphry Davy in similar experiments with alkali in 1897 extracted new unknown chemical elements natrium and potassium. Therefore as a result of the 18-th century a solid background for next very important discoveries such as electromagnetism was created. V. CONCLUSIONS 18-th century brought us a lot of very useful electrical knowledge and inventions: 1. At first P. Muschenbroek created the very powerful potential generator called the Leiden jar. 2. B. Franklin employed this device to understand the electricity as one sort of “electrical fluid” which over plus appears as a “glass” or positive electricity and a deficit as a “resin” or negative electricity. 3. The greatest B. Franklin discovery was a lightning electrical nature proving and a lightning rod invention as the first real electrical science application. 4. Transformation of electrical phenomena descriptions into a precise science discipline happened due to C. Coulomb’s experiments and his law of interacting charges. 5. The new breakthrough was made by L. Galvani opened “animal electricity” in his experiments with frogs. 6. These experiments true explanation by A. Volta brought him the idea about an electrical cell – the first electrochemical current generator. 7. Other very useful Volta’s inventions were a condenser and an electrometer – the first voltmeter. 8. His followers V. Petrov, H. Davy and other demonstrated an electric arc, a water decomposition and new chemical elements discovery - natrium and potassium.
VI. REFERENCES [1] A.G. Mikerov, From the history of Electrical Engineering: Electricity and Magnetism in Old, Middle Ages and Renaissance, Proceedings of the Russia North West Section, v. 3, 2012. [2] B.I. Spasskiy, History of physics, vol.1. Moscow, Russia: Moscow University Publishing House, 1963 (in Russian). [3] V.P. Kartsev, Great equations adventures. Moscow, Russia: Znaniye Publishing House, 1978 (in Russian) [4] The Project Gutenberg EBook of The Inspector-General, by Nicolay Gogol. [Online]. Available: http://www.gutenberg.org/ebooks/3735 [5] The Project Gutenberg EBook of The Storm, by Aleksandr Nicolaevich Ostrovsky. [Online]. Available: http://www.gutenberg.org/cache/epub/7991/pg7991.txt [6] The most famous men and women in American history. EMSWORTH. [Online]. Available: http://emsworth.wordpress.com/2008/06/09/a-better-list-offamous-americans-men-and-women/ [7] Health indicator – schematic diagrams and descriptions (in Russian). [Online]. Available: http://shemki.ru/readarticle.php?article_id=74 [8] Luckiesh, Matthew Artificial light, its influence upon civilization. New York: Century, 1920.
