Text 15 A The Atomic Theory - раздел Образование, Part One THE PREDICATE In 180S The English Chemist And Physicist John Dalton (1766-1844) Put Forward...
In 180S the English chemist and physicist John Dalton (1766-1844) put forward the hypothesis according to which all substanccs were stated to consist of small particles of matter, of several different kinds, corresponding to the different elements. He called these particles atoms, from the Greek word atomos, meaning "indivisible". This hypothesis gave a simple explanation or picture of previously observed but unsatisfactorily explained relations among the weights of substances taking part in chemical reactions with one another. As it was verified by further work in chemistry and physics, Dalton's atomic hypothesis became the atomic theory.
The rapid progress of scicncc during the twentieth ccntury is well illustrated by the increase in our knowledge about atoms. In a popular textbook of chemistry written in the early years of the twentieth century, atoms were defined to be the "imaginary units" of which bodies arc aggregates. The article in "Atom" in the 11 th edition of the Encyclopaedia Britannica, published in 1910, ends with the words "The atomic theory has been of priceless value to chemists, but it has more than once happened in the history of science that a hypothesis, after having been useful in the discovery and the coordination of knowledge, has been abandoned and replaced by one more in harmony with later discoveries. Some distinguished chemists thought that this fate may be awaiting the atomic theory... But modern discoveries in radioactivity are in favour of the existence of the atom, although they lead to the belief that the atom is likely to be not so eternal and unchangeable a thing as Dalton and his predecessors had imagined".
Only half a ccntuiy later, scientists had precise knowledge of the structure and properties of atoms and molecules. Atoms and molecules can no longer be considered "imaginary".
