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GIANTS OF HUMAN CIVILIZATION 2

Dr sci. SIMO JELAČA

DEMOCRITUS (460-370 BC), Greek philosopher

Democritus, like many others from that time period, did not leave many written traces of his activities. Others wrote more about him, Aristotle among the first. Democritus was the first to use the word atom (in Greek atomon) for the invisible parts of matter. According to Democritus, the universe consisted of a vast vacuum with an unlimited number of atoms, which constituted the physical world. Democritus believed that atoms are the constituent parts of everything on earth, as well as planets and stars. He claimed that atoms are unchanging, solid and invisible. He argued that atoms in different ratios make up rocks, plants and animals. After the death of living organisms, their atoms become free to form other forms. He also argued that atoms in different things exist in different combinations. For liquid substances, he declared that they are smooth and that they enter between other atoms. He gave similar descriptions for tasty substances and different colors.

The significance of Democritus is that he was one of the first to reject religious and spiritual teachings. He even described the human soul as the rapidly moving atoms in the human body. According to him, after death, the atoms of the soul separate and form another being. Democritus attributed all human activity to the mobility of atoms in the body.

And although modern science has disproved many of Democritus' teachings, he is remembered as the first to try to explain the universe with simple physical and mathematical laws. And that led to a change of opinion and a proper orientation towards scientific studies.

Democritus is also credited in the domain of mathematics for proving that the volume of a cone is equal to one third of the volume of a cylinder of the same base and height, as well as for similar relationships with pyramids and prisms.

PLATO (427-347 BC), Greek philosopher

Plato is said to have been born near or in Athens and to have left Athens in 399 BC, after the execution of Socrates. After twelve years he returned to Athens and opened his Academy in 387 BC, which became a bastion of intellectual achievement. It lasted until 529 AD (almost a whole millennium), when Justinian closed it on his orders. Some historians consider Plato's Academy to be the first university in Europe. In it, the true principles of learning in the domains of science and philosophy were laid out, and above its entrance was written: "Let not those who ignore geometry enter." Plato's Academy became a leader in mathematics, astronomy, science and philosophy. During Plato's youth, Athens flourished as the world's most dominant cultural center.

Plato's teaching is based on the claim that nature, as seen by the human eye, is true. Like Pythagoras and Plato, he favored science and rational mathematics, which constituted universal truths. In this way, arithmetical calculations could predict future discoveries, similar to how elements that had not yet been discovered could be predicted according to Mendeleev's system.

Plato is remembered today as one of the greatest philosophers of the Western tradition. His influence was felt in all academic disciplines, in education and literature, in aesthetics, and even in political thought, and his logical approach to science remains as a testament to hard-to-understand ideas.

ARISTOTLE (384-322 BC), Greek philosopher

Aristotle's scientific ideas took on an almost divine character. At the age of 17, he entered Plato's Academy in 367 BC, and after Plato's death in 347 BC, he left the Academy and became a private tutor to the young Alexander the Great. Aristotle opened his school in Athens in 335 BC, called the Lyceum. At that time, the Western world was dominated by Aristotle's thinking in the domains of physics and cosmology, which remained until the time of Galileo and Newton. Aristotle's teaching was based on the assertion that everything that exists consists of four elements: earth, water, air and fire. And Aristotle accepted the claim that the Earth is at the center of the universe, and that the Sun, Moon and planets revolve around the Earth. He considered that stones, as the heaviest, are in the center of the earth, water, as the lightest, floats on the surface of the earth, and air, as even lighter, is above the earth and that fire tends to rise to the heights. Aristotle also introduced the concept of aether, arguing that the moon moves in the aether, and this opinion persisted for two thousand years after him.

Pythagoras established that the earth has a spherical shape, and Aristotle himself noticed that the earth's shadow on the moon during a lunar eclipse has a slightly flattened (elliptical) shape. In the field of biology, Aristotle was the first to classify animals according to their reproduction (birth of live young or brood from eggs).

EUCLIDS (330-260 BC), Greek mathematician

Euclid was Plato's student in Athens, while he spent most of his life working in Alexandria, Egypt, where he founded a mathematical academy. His famous work is the Elements, which had a huge influence on Western academic thought. Elements is said to be the most studied, translated and printed work in human history after the Bible. It has seen 1700 editions. Euclid systematically described what he studied, from the obtained conclusions he established several axioms and derived theorems. Such a logical method of research work has been preserved to this day. The Elements were written in thirteen volumes, and in them Euclid presented the findings of his predecessors, Pythagoras and others, in the form of systematic proofs, theories and original findings. In the first six volumes, he dealt in detail with plane geometry: triangles, squares, rectangles, circles, as well as the theory of proportions. The next four volumes cover various theories, including the theory of unbounded numbers. The last three volumes deal with the geometry of bodies. Some of Euclid's axioms (such as the parallelism theorem) were disproved in the nineteenth century, and Albert Einstein declared that Euclid's geometry did not apply in space.

ARISTARCHUS (310-236 BC), Greek astronomer

Aristarchus was the first to calculate the sizes of the planets and their distances in the solar planetary system. He arrived at this by using the positions of the Sun, Moon and Earth at the moments of total solar and lunar eclipses. In a very original way, he calculated the mutual distances of the heavenly bodies as a function of the diameter of the earth, and the diameter of the earth with the help of his device called the skiff and the well in Siena. Aristarchus discovered that at half the light of the Moon, the Moon makes an angle of exactly 90° to the Sun and the Earth, while the angle from the center of the Earth to the Moon and the Sun is 87° (the modern angle is believed to be 89 °51'), and the angle from center of the sun towards the earth and the moon 3°. With this, he established that the diameter of the earth is 2.8 times greater than the diameter of the moon, and the diameter of the sun is 19 times greater than the diameter of the moon or 6.8 times greater than the diameter of the earth. Further, Aristarchus calculated the volumes of celestial bodies, such as spheres, and found that the volume of the earth was 22 times the volume of the moon, and the volume of the sun 6860 times the volume of the moon, or 312 times the volume of the earth. In the work on the radius of the earth, he calculated that the distance of the moon from the earth is equal to 81 radii of the earth, and the distance of the earth from the sun to 1550 radii of the earth. Aristarchus was the first to argue that the Earth moves around the Sun, following a heliocentric path, and not the other way around, from west to east. He also claimed that the sun obviously moves. Aristarchus' teaching became an integral part of science in Alexandria, where he worked from 280 to 260 BC. Aristarchus also presented the first evidence that the seasons on earth were a result of the earth's ecliptic (which is the angle the earth's equator makes with the plane of the earth's path). Through his calculations, he came to the conclusion that the universe is infinite. Aristarchus surpassed Aristotle in his works, which disturbed the Alexandrian scholars and they accused him in front of all Greece. Because of all this, he was exiled to an unknown island in 260 BC, which is why the year of his death is not known with certainty. It is known that he became the director of the philosophical school in Athens in 264 BC. It was later confirmed that Aristarchus' system of the world was identical to Copernicus's, only that he thus preceded Copernicus by 17 1/2 centuries. Unfortunately for civilization, many of Aristarchus' teachings, as well as many others, were lost in the fire of the famous Library of Alexandria in 392 AD. Our distinguished scientist Milutin Milanković in his work "Through the Universe and the Ages" has very successfully reproduced Apollonius' theorem on the epicyclic motion of the planets of the Solar System, in which way the so-called Star real estate. Accordingly, the stars give the impression that they move in one direction, then stop and after a certain time move in the opposite direction. This confirmed Aristarchus' findings that the stars are extremely distant from our solar system.

According to the aforementioned report of Aristarchus, there is a claim that in the south of Egypt, in the place of Syene, there is a very deep well in which the Sun is reflected only once a year, exactly at noon of the longest day. year. This means that at that time, in that place, there is no shadow of the object, due to the zenith position of the sun. Aristarchus made a device, called a scapha (sundial), which represents a regularly concave hemisphere, with a central rod as a pillar and marked meridian circles. At noon on the longest day of the year in Alexandria, he measured the length of the shadow of that stick in the skiff and from the geometrical relationship between the size of the given shadow and the distance from Alexandria to Siena, which was 5000 stadia, he calculated the circumference and diameter of the earth. And Aristarchus confirmed in this way that Greek scientists observed, thought and calculated, and left the "paid" work to others. And that's what makes them great.

ARCHIMEDES (287-212 BC), Greek mathematician

Archimedes was a brilliant researcher, mathematician and inventor in his day and is remembered as perhaps the greatest mathematician of all time. The first established that the volume of the ball is equal to V=4 / 3 r3 p =⅙ d3 p, where r is the radius of the ball, i.e. equal to 4/3 of the volume of the described cylinder, and that the surface of the ball is equal to four times the area of its largest circle. Archimedes found the value of the number p approximately equal to 3.142857...He determined that the volumes of a cup, hemisphere and cylinder, with the same base and height, are in the ratio 1: 2: 3.

Archimedes also established the famous physical law, according to which any body immersed in a liquid is pushed by a force equal to the weight of the liquid it displaces. There is a recorded story that when he found it, while he was bathing, out of great excitement he ran out into the street and ran and shouted: "Eureka, Eureka" (meaning: I discovered). In addition, he studied the laws of levers, pulleys, wedges, screws and the method of determining the center of gravity of a body (center of gravity). Archimedes was killed by a Roman soldier while doing mathematical calculations for the defense of Syracuse and his last words were, "Don't touch my circles."

Archimedes' discoveries include:

Archimedes screw: a device used for pumping water from ships and for irrigation; Archimedes' gun: a device for sinking ships, used in the defense of Syracuse; Multi-cell system: a device for lifting large loads with low force; Methods of calculating surfaces and volumes of images and bodies;

Archimedes' law in hydrostatics, as well as the discovery of pycnometry (measurement of body volume and density);

Integral calculus, which was later used by Kepler, Fermat, Leibniz and Newton. Our respected scientist Milutin Milanković ranked Archimedes among the greatest geometers of the ancient century.

APOLLONIUS OF PERGA (265-170 BC), Greek astronomer

Apollonos of Pergeia is considered one of the greatest geometers of the ancient century. He was born in Perga, and as a young man he came to Alexandria where he was educated by Euclid's students. There he also wrote his work on conic sections, a magnificent monument of Alexandrian science. He also wrote many other works that unfortunately failed, including Zbornik. He worked at the Alexandria Museum, which acted as the Academy of Sciences. It was based on the teaching of Aristarchus and answered the problem of the movement of distant stars, observed from the earth, which also move around the Sun. Apollonius' interpretation was vividly illustrated and explained by Milutin Milanković in his work History of Astronomical Science (pp. 339-343), and it is preserved in the twelfth book of Ptolemy's collection. The so-called stars of immobility move along an Archimedean spiral, that is, one gets the impression that they move in one direction, then stop and then return, continuing the spiral movement (see picture on page 340 M. Milanković). According to the interpretation of Apollonius, the planets of the solar system move in elliptical paths around the sun, a theory that was later developed by Johannes Kepler (1571-1630) and is still valid today.

HIPPARCHUS (170-125 BC), Greek astronomer

Hipparchus is considered one of the most influential astronomers of the ancient world. His research covers the fields of mathematics and geography. He was the first to mark places on a map of the Earth, using longitudes and latitudes (which was consistent with Aristarchus' geocentric system of planetary motion). He recorded his geographical investigations of the trigonometric spheres of the planets he studied. He compiled a table of coordinates, according to which he calculated the distances of points on circular lines and the corresponding angles from those points to the center. He was the first in geometry to introduce the value of a circle of 360°, as well as the concepts of minutes and seconds, as parts of an angular degree, of 60 units each. Hence, he is considered the founder of geometry and trigonometry. The first also determined the Earth's equinoxes and determined the length of spring at 94.5 days, summer at 92.5 days and autumn at 88 days, and winter at 90 days (a total of 365 days), while the Chaldeans for the northern hemisphere determined the length of spring and summer at 186 d and 10 h, and in autumn and winter from 178 d and 20 h (365 d and 6 h in total).

ZHANG HENG (78 BC-138 AD), Chinese astronomer

Zeng Heng corrected the Chinese calendar in 123 AD, in accordance with the seasons, and in 132 AD he found the first seismograph to measure the strength of earthquakes. As early as 138 AD, his seismograph registered an earthquake at a distance of 500 km. He also, independently of Archimedes, calculated the value of the number (pi) ∂ = 3.162, which before him was simply calculated as ∂ = 3. He was also the first to construct a device for recording the distance traveled. In addition to all that, he was engaged in painting and wrote about twenty literary works.

To be continued

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