John Dalton
Instead of calling the water molecule "two atoms of hydrogen and one atom of oxygen," we call hydrogen "H" and oxygen "O" and write, simply, H2O. The symbol for carbon is "C" and carbon dioxide may be written CO2. This means that one carbon atom and two oxygen atoms combine to form one molecule of carbon dioxide.
John Dalton was a great scientist and almost everything in his atomic theory turned out to be correct. Only one of his ideas we now know to be wrong. And that idea went all the way back to Democritus. They both thought that the atom was the smallest possible particle, and that it could never be divided.
It certainly seemed to be so. But astonishing things about atoms began to turn up around the end of the 1800's. No one knew it yet, but men were going to change atoms—and atoms were going to change the world!
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THE MYSTERY OF THE RAYS
In 1895, a German scientist, Wilhelm K. Roentgen (RENT-gen), was experimenting with a special kind of electrical tube. He had covered one end of the tube with black paper. Nearby was a screen that glowed when light shone on it.
Roentgen happened to glance at the screen—and could hardly believe his eyes. It was glowing—but there was no light coining from the covered tube! This seemed impossible—but there it was.
Later, when someone asked Roentgen what he thought, he made a true scientist's reply.
He said, "I did not think. I investigated!"