1. Ancient Greek philosophers like Democritus, Leucippus, and Epicurus developed early atomic theory, proposing that all matter is made of indivisible, eternal atoms moving through empty space. 2. Democritus is considered the greatest of the ancient atomists, describing atoms as having different shapes, sizes, and arrangements which determined the nature of materials. 3. Aristotle strongly opposed atomic theory, instead proposing that all matter is made of various combinations of qualities like dryness and wetness. This view came to dominate for many centuries until atomic theory was revived in modern times.

1. ANCIENT ATOMISTS<br />\"
There is nothing but atoms and space,everything else is only an opinion'- Democritus from Abdera <br />To get the most exact understanding and become acquainted with the development of thoughts in atomistics one should go back in time for over two thousand years and come to know attainments of ancient Greek philosophers. They were the first to research the world of microstructure. The researches were in considerable range ( but not always ) limited to solely logical considerations not supported by any experiments or discerning observations of nature. That caused many contradictions and often divergences between theory and practice.<br />Thales from Miletus ( 620?- 540? B. C. ) was one of the first Greek thinkers, who started to considerate world's microstructure. He described the electrical influence of amber electrified by rubbing. He recognised water as basic substance occurring in nature. He thought that water was an original and final element and all the other substances came out of it. Life descended from water which in turn was a source of all motion. It had features which let the nature develop. He maintained that force was united with matter. He was of the opinion that the basic characteristic of water was its ability to move.<br />Anaximander from Miletus (611- 547 B. C. ), Thales's disciple, perceived the world as the composition of contrasts : dry and wet, hot and cold; and one couldn't come from the other. It would be a mistake to declare that any one of them is the basic element. But he believed in the subsistence of the basic substance -apeiron- great, infinite in time and space, undiverted and neutral immensity. [ Although as the basic substance apeiron had strange features it resembles something well known nowadays- vacuum ! ] According to Anaximander the apeiron filled the whole world and created all the other substances which later disappeared in it, and included oppositions which could separate. He maintained also that matter was combined with motion making a unit.<br />Anaximenes from Miletus (570?- 526 B. C. ), next of Thales's disciples, maintained that the basic substance was not water or apeiron but air. It was to be infinite in quantity. That was confirmed by his observations of nature. All other things could be created in the process of air thickening (during cooling it down ); and in the process of rarefying it (during warming it up ). For example, fire was created during the process of air rarefying but winds, clouds, water, earth and other solid substances by the process of air condensation. The thermal conversions were connected with everlasting movement in the universe. He used mentioned above considerations to explain meteorological occurrences.<br />Heraclitus from Ephesus (540?- 480 B. C. ) considered fire the original substance. He came to the conclusion hat fire could change into all other elements and substances while coming through the universe from its top to bottom ( fire changed into air, air into water and water in to earth ).<br />Xenophanes from Colophon (575?- 480? B. C. ) considered earth- the fourth element- the original substance.<br />Parmenides from Eleusis (540?- 470? B. C. ) maintained that being, which was everything perceptible for the mind, didn't have the beginning and was unchanging. He thought that being was not connected with time and spreaded over everything. He also maintained that no substance could change into other. This image of the world was not in agreement with the observations ( f. e. , wood burns down, water evaporates- nothing is unchanging ), therefore he stated that one shouldn't believe his senses but only his reason.<br />Empedocles from Acragas ( 490?- 430? B. C. ) maintained that matter consisted of four substances. Those four were to be the elements : earth, fire, water, and air. None of them had the right to change into another, and all other things were built from those four elements combined in different proportions. For example, bones are made of two pieces of earth, two pieces of water and four pieces of fire. After their combination the new substance is created, but the elements stay unchanging. He stipulated the subsistence of two original forces :love and discord necessary for world's existence. The forces were working by attracting and repelling. Love combined common particles and hate repulsed different particles. He was against the theory of vacuum.<br />Anaxagoras from Clazomenae (500?- 428 B. C. ) stated that world's components were unchanging. Just like Empedocles he was of the opinion that particles could combine with each other and disintegrate. But he thought that each and every substance had its own kind of particle, called by him 'nucleus'. There was the infinite number of them and they could be divided endlessly. Each and every particle contained all the other particles indifferent proportions. For example, eating particles of meat one eats also the particles of muscles, bones and blood, building up his organism in this way.<br />Leukippos (probably about the 5-th century B. C. ) asserted that world consisted of indivisible particles of matter. They should have geometrical shapes and were called 'schematones'. He said that they had definite place in space. They were not detected by senses because they were not connected with them, but with reason. They sent secondary particles which got to one's soul leaving there the reflection of the external world. He postulated also the subsistence of some empty space where elementary particles could be placed. The void was needed to let the particles move. He laid the foundations of the theory explicated later by Democritus.<br />Democritus from Abdera (460?- 370? B. C. ) was the greatest Greek philosopher in researching microcosmos. Indeed, it is from his times that development of atomistics dates. He described his theory in the work entitled 'On the Little Order of the World '. He maintained that nothing could change into something absolutely different. He saw nature as the ceaseless motion of small, material, indivisible and eternal particles which he called atoms because 'atomos' means 'indivisible' in Greek. Atom could not be created nor annihilated. It was unchanging. He believed that atom was the basic brick of matter. It had a shape and the place in space. It had also some mass. Atoms couldn't be identical, but of different shapes and sizes. These differences were influencing features of materials. He stated that white things were made of smooth atoms and black of rough ones. Sweet things were made of spherical atoms and bitter of angular ones. He also believed that life consisted of very small, round, smooth atoms and soul was mode of the smallest particles of air and heat. Later on Democritus ascertained that hard things were made of many atoms without much space between them and soft things were made of loose atoms. Then he said that particles situated in empty space could move all the time with similar atoms approaching and different repulsing; sometimes colliding, bounding and gathering into groups. For him the universe was an act of perpetual gathering and diffusing of atoms kept in everlasting motion.<br />Epicurus (342- 270 B. C. ) maintained that there were indivisible atoms having their own size, weight and shape. Everything in the universe was made of them including human's body and soul. In empty space atoms could move uniformly up and down thanks to the gravitation. But they could also abberate at random and turn. Such description of the movement of particle made randomness and freedom possible.<br />A Roman; Titus Lucretius Carus ( 95?- 55 B. C. ) was a continuator of Epicurus's philosophy. He wrote a poem 'On the Constitution of the Universe' in which he enclosed his considerations on world's nature. He explained all occurrences on the basis of atomistics theories. Thanks to his work the opinions of Democritus and Epicurus penetrated the Roman Empire and consolidated there.<br />Aristotle (384- 322 B. C. ) was a great Greek philosopher especially respected in Middle Ages. He was a resolved opponent of Democritus's atomistics. He stated that world couldn't consist of small, indivisible particles because if so they should fell down like a thrown up rock did. He was of the opinion that there were four basic qualities determining the constitution of substance. Those four were to be : dryness, wetness, heat and cold. For example, fire consisted of heat and dryness; water consisted of cold and wetness. The conversion of water into steam he explained in that way : The heat of fire joins the wetness of water creating air and earth (the last one can be found at the bottom of the pot after vaporising the water ). Those qualities were abstract. The vision created by him buried Democritus's theories for many centuries.<br />Greek philosophers' attainments in the field of world's construction, although rather philosophical than natural scientific, were great. Only uncommon people could dare to make an attempt to understand and describe rationally the universe. The attainments of the philosophers began the history of atomistics' development. The conception of atom was formulated. Philosophers tried to describe it but without the possibility of checking the presumptions experimentally. It led to many different, contradient theories. One can say that every philosopher had a different opinion on microstructure. Unfortunately, in Middle Ages people chose wrong theory ( Aristotle's one ). Nevertheless Democritus's works prevailed again in contemporary times influencing scientists.<br />