In order for man to learn to produce and control nuclear energy himself, however (something that did not take place until this century), three lines of investigation—atoms, electricity, and energy—had to develop and meet.
We will begin with atoms.
ATOMIC WEIGHTS
As long ago as ancient Greek times, there were men who suspected that all matter consisted of tiny particles which were far too small to see. Under ordinary circumstances, they could not be divided into anything smaller, and they were called “atoms” from a Greek word meaning “indivisible”.
It was not until 1808, however, that this “atomic theory” was really put on a firm foundation. In that year the English chemist John Dalton (1766-1844) published a book in which he discussed atoms in detail. Every element, he suggested, was made up of its own type of atoms. The atoms of one element were different from the atoms of every other element. The chief difference between the various atoms lay in their mass, or weight.[1]
Dalton was the first to try to determine what these masses might be. He could not work out the actual masses in ounces or grams, for atoms were far too tiny to weigh with any of his instruments. He could, however, determine their relative weights; that is, how much more massive one kind of atom might be than another.
For instance, he found that a quantity of hydrogen gas invariably combined with eight times its own mass of oxygen gas to form water. He guessed that water consisted of combinations of 1 atom of hydrogen with 1 atom of oxygen. (A combination of atoms is called a “molecule” from a Greek word meaning “a small mass”, and so hydrogen and oxygen atoms can be said to combine to form a “water molecule”.)
John Dalton
To account for the difference in the masses of the combining gases, Dalton decided that the oxygen atom was eight times as massive as the hydrogen atom. If he set the mass of the hydrogen atom at 1 (just for convenience) then the mass of the oxygen atom ought to be set at 8. These comparative, or relative, numbers were said to be “atomic weights”, so that what Dalton was suggesting was that the atomic weight of hydrogen was 1 and the atomic weight of oxygen was 8. By noting the quantity of other elements that combined with a fixed mass of oxygen or of hydrogen, Dalton could work out the atomic weights of these elements as well.