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GIANTS OF HUMAN CIVILIZATION 6

Dr sci. SIMO JELAČA

WILLIAM AND CAROLINE HERSCHEL (1738-1821 and 1750-1848), British astronomers

Both were born in Germany, British by nationality, William and Caroline Herschel were remembered for discoveries in the field of astronomy, namely William discovered the planet Uranus after the discovery of the telescope, and Caroline discovered eight comets after William's death.

DOSITEJ OBRADOVIĆ (1739-1811), creator of Serbian identity

Dositej Obradović was born in Čakovo in Banat, lost his parents at an early age and fled to the Hopovo monastery in Fruškogorsk, where he became a monk. He was also interested in church literature and Serbian history, especially Dušan's code. He went into the world relatively early, already in 1761, and stayed there for 40 years. In Halle, Germany, he adopted the slogan "Education to Freedom". He worked as a teacher, doctor, proofreader, lecturer and became a polyglot, he learned: Greek, Latin, German, English, French, Russian, Albanian, Romanian and Italian.

Dositej Obradović is remembered in Serbia as the founder of the first school in Serbia and as the first Serbian modern writer. He is the founder of the Belgrade Lyceum and the first minister of education in Serbia. He also helped establish the Great School in Belgrade in 1808 and opened the Belgrade Theological Seminary. He personally took care of the education of Karađorđe's successor, Aleksa's son. Before his death, he also worked on the opening of the first printing house in Belgrade. Dositej Obradović paved the way for the activity of Vuk Stefanović-Karadžić and was the first in Serbia to start writing in the vernacular, a simple vernacular dialect. Hence, Dositej and Vuk are considered the founders of modern Serbian culture.

He traveled a lot, staying in Corfu, Mount Athos, Peloponnese, Izmir and Karigard, Venice, Zadar, Vienna, Karlovci, Bratislava, Trieste, Leipzig and Halle, Paris, London and many other places. The most important written works of Dositej are: Life and connection; Letter to Charalampius; Common sense Soviets and others. Jovan Skerlić said of Dositej that in his lifetime he saw and knew more than any living Serb.

JOSEPH MONTGOLFIER (1740-1810), French balloonist

Brothers Joseph and Etienne Montgolfier were the first inventors of a hot air balloon, which took off with a man in 1783. The first balloon was made on the basis of hot air, although experiments were also carried out with hydrogen. Their compatriot Jacques-Alexandre-César Charles made a flight in a hydrogen-based balloon a little later.

KARL WILHELM SCHEELE (1742-1786), Swedish chemist

Carla Silla is credited with the discovery of oxygen, two years before Joseph Priestley, in 1772, but it was not immediately published. After that, he discovered chlorine in 1774, and in 1775 he was accepted as a member of the Stockholm Academy of Sciences. Sile is also credited with discovering the effect of light on silver salts, which later became the basis for the development of photography. It was written about Silet that he was literally ready to die for science.

ANTOINE LAVOISIER (1743-1794), French chemist

Lavoisier was the most respected chemist of his time, yet he ended up on the guillotine. Lavoisier is still considered the founder of modern chemistry. His conclusions led to a restructuring in chemistry, similar to Newton's effect in physics. Lavoisier's first studies involved measuring the gain or loss during heating and combustion of substances. These experiments led to Lavoisier's law of conservation of matter. Then he experimentally proved that solid substances gain mass during combustion, and the result is the reaction of binding gases from the air (mainly oxygen). He also determined the presence of nitrogen in the air, as a neutral gas. He summarized his findings in Elementary Treatments in Chemistry. This confirmed that oxygen is a vital component in the processes of respiration and combustion. He also summarized the previous findings of French chemists and confirmed that water is a combination of hydrogen and oxygen. With this finding, he came into conflict with Cavendish and James Watt, who had made the same discovery before Lavoisier. While working as a research chemist, Lavoisier also worked for a tax collection company, so he came into conflict with the French revolutionaries, who sentenced him to death by guillotine. Unfortunately, this is how one of the most famous French scientists ended up.

ALESSANDRO VOLTA (1745-1827), Italian physicist

Volta is the inventor of static electricity storage batteries. He studied the findings of Luigi Galvani, but rejected his claims that toothed drums retained electricity. Volta, on the other hand, determined that different metals are an important factor for the production of electricity. Incidentally, Galvani and Volta were personal friends and Galvani sent his findings to Volta for review, expecting a positive response. However, there was a disagreement. While making battery cells, Volta placed his tongue between metal electrodes to determine the flow of current. With this, he discovered that in liquid batteries with silver and zinc electrodes, when the circuit is closed, current flows. For these achievements, Napoleon declared Volta a count and then a senator of Lombardy and awarded him the Legion of Honor.

EDWARD JENNER (1749-1823), English physician

Edward Jenner is the doctor who created the world's first vaccine. He studied angina, and he made his greatest discovery by experimenting with smallpox. In his time, every fifth resident died of smallpox, and there was no natural cure. It was noticed that the survivors could not get the same disease a second time, so the first experiments went in the direction of infecting open wounds with smallpox. However, this procedure proved to be risky. In 1796, Dr. Edward Jenner heard an anecdote that nursing mothers who had chicken pox could not get small pox. Chickenpox was known to be a mild form of smallpox and did not cause death. On May 14, 1796, Mrs. Sara Nelmes, a nurse who was suffering from chicken pox, came to Dr. Jenner's office. The doctor removed her milk and convinced the eight-year-old boy's father to infect him. As expected, the boy contracted a mild form of chicken pox and recovered quickly. Soon after, Dr. Jenner infected the same boy with a latent dose of smallpox. There was no illness. The doctor repeated his experiment after a few months on the same boy, but the smallpox did not appear. Although he did not yet know the correct course of action, Dr. Jenner concluded that vaccination was the correct method of combating smallpox. Then in 1798 he published the work "An Inquiry into the Causes and Effects of Variolae Vaccinae", which led to its mass acceptance, and since 1900 it has become the only way to fight smallpox in the world.

ALEXANDER MACKENZIE (1764-1820), Scottish-Canadian explorer

Alexander Mackenzie is the first person to cross the North American continent, from northern Canada to Mexico. He immigrated to Canada from Scotland and took a job with the Hudson's Bay Company, a fur trading firm, before setting out on a voyage to explore a waterway to the Pacific. He visited the Great Lakes in 1789, where he discovered a westward flowing river. He began to follow its course, but was disappointed when he discovered that it flowed in a northerly direction, in the Arctic. That river was later named Mackenzie River after him. His discoveries later helped open the Pacific North to European immigration.

JOHN DALTON (1766-1844), English chemist

Dalton's atomic theory transformed the foundations of chemistry and physics. At the beginning of the nineteenth century, the Englishman Dalton investigated the solubility of gasses in water. He believed that gasses were in the form of atoms, according to an idea that had been valid since Democritus (460-370 BC). Dalton, however, provided an explanation for the entry of elemental gasses into compounds during chemical reactions. He published his theory in 1803, and published the book "New System of Chemical Philosophy" in 1808. His explanation is: "Atoms of the same elements are identical, they are not created or destroyed, everything is made of atoms, chemical changes." are simply the displacement of atoms and compounds are composed of atoms of the corresponding elements". In the same book he summarized the previously known elements with their atomic weights, compared to hydrogen, whose weight he adopted as a unit. Thus carbon had an atomic weight of 12, oxygen 16, etc. Dalton, however, wrongly concluded that the elements always reacted in a one-to-one ratio, according to which the water molecule was HO, not H2O air consists of mixed gasses, not compounds, and he was the first to confirm the equal expansion of all gasses at an equal rise in temperature.He was also the first to determine the dew point.

ANDRE-MARIE AMPERE (1775-1836), French physicist and mathematician

Hans Christian Oersted (1777-1851) was the first to notice that a magnetic needle was removed when a current was applied. Michael Faraday (1791-1867) was the first to apply Oersted's discovery, but it all remained unexplained until Ampere's interpretation. He founded the branch of electromagnetism in science. Ampère was a brilliant mathematician and taught mathematics in his native Lyon, France. Since 1802, he has been a professor of physics and chemistry, and Napoleon appointed him inspector at the university. Dealing with electromagnetism, he defined it mathematically and called it electrodynamics. Ampere noticed that one current affects another. He also found that two magnets affect each other. Hence, he began to see these two phenomena as similar events. He then passed currents through two parallel conductors and found that if the currents are in the same direction, the conductors attract, and if the currents are in opposite directions, the conductors repel. This discovery resulted in Ampere's law of 1827, which opposes Newton's law of universal gravitation. It has been proven that between two electric conductors there is a magnetic force proportional to the current product, and inversely proportional to the root of their distances. Ampère innovated the solenoid, and in his honor the unit of current strength "Ampere" was given in the SI measurement system.

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AMEDEO AVOGADRO (1776-1856), Italian physicist

The Italian Avogadro was the first to establish the theory of the volume of gasses in 1811, but after that it remained neglected for half a century. Avogadro combined two incompatible hypotheses of Joseph Louis Gay-Lissac and John Dalton. Gay-Lissac assumed that gasses always bind to each other in whole number ratios (2:1 or 2:3), and never in fractional ratios, at the same temperatures and pressures. Dalton did not accept this interpretation, arguing that gasses only react in one-to-one atomic ratios. At that time, the concept of molecule was not yet clear, and oxygen and hydrogen exist in nature only in molecular forms (H2 and O2). Avogadro noted that the term molecule explained the Gay-Lyssac statement, according to which four hydrogen atoms bind two oxygen atoms, giving two molecules of water (2 H2 + O2 = 2 H2 O).

According to Avogadro's law, at the same pressure and temperature, equal volumes of all gasses have the same number of molecules.

It was not until 1860, when Stanislao Cannizzaro discovered Avogadro's unpublished results of his work, and published them at a meeting of chemists, that the law was accepted. This eliminated misunderstandings about the concept of atoms and molecules and their relative atomic or molecular weights. Avogadro's number, as a constant that shows the number of particles as moles of each substance is 6.0221367(36) x 10″≥ adopted after that.

HANS CHRISTIAN OERSTED (1777-1851), Danish physicist

Hans Christian Oersted was the first to discover the concept of electromagnetism. He graduated in physics and pharmacy in Copenhagen, and later became the director of the Polytechnic Institute. He gave popular public lectures, and in 1820 he accidentally discovered that a compass needle deviates when a battery is ignited nearby. He then established that an electric current creates a magnetic field around an electric conductor. This discovery soon became the guiding idea of ​​scientists Ampere and Faraday.

JOSEPH GAY-LUSAC (1778-1850), French chemist and physicist

Gay-Lissac was heard in science after the publication of Charles and Boyle's law (Alexandre Jacques--Cesar Charles & Robert Boile). According to this law, a certain amount of any gas expands by an equal amount when the temperature rises, at constant pressure. Also, when lowering the temperature, the volume of all gasses decreases in the same ratio, until the temperature reaches absolute zero (-273.16°C), at which temperature their volume becomes equal to zero. Therefore, the Kelvin temperature scale adopted this value for absolute zero, which is theoretically the lowest temperature that can be reached. This law was published at the same time as John Dalton's discoveries, so Dalton intended to discredit Gay-Lissac because it conflicted with his atomic theory, but in the meantime Avogadro published his theory of atoms and molecules in 1811, which united both previous conclusions.

Gay-Lissac and his compatriot, the Frenchman Thenar, discovered the elements boron and iodine, and in 1815 they also discovered cyanide, disproving Lavoisier's claim that all acids must contain oxygen. In his later research, Gay-Lissac focused on the reactivity of nitrogen and sulfur, as well as the fermentation process.

                                                                                                To be continued...

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