Experiments with frogs.. 

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... f N gravitation force, R distance between masses, k N - 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 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]. 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]. 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. 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 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. 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 curr ents 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. 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 Volta ’s achievements and contributions were commemorated as following:  P otential difference is called as a “voltage” and its value in the SI system is measured in volts.  V oltage instrument name is a “voltmeter”. Even an electric arc has the name a “voltaic arc” while Volta had no relation to its invention. 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 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. 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. 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. C ONCLUSIONS 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 appear s 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 an d 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 ...