In the 19th century there were only few scientists still not believing in atoms' subsistence. There was already much evidence for the hypothesis of an atom. As it was said before the word "atom" derives from the Greek word "atomos" meaning "indivisible". But were the atoms imagined by Dalton and Mendeleev really indivisible, and without internal structure? Scientists of the 19th century thought they were. But already in 1896 it emerged that they were wrong.

In 1838, Michael Faraday passed current through the glass tube filled with rarefied air. Conducting the experiment he noticed a strange light arc with its beginning at the anode (the positive electrode) and its end almost at the cathode (the negative electrode). The only place where there was no luminescence was just in front of the cathode. The place is called "cathode dark space", "Faraday dark space", or "Crookes dark space". That was the beginning of the long and "turbulent" time of researches on that luminescence. And the luminescence is called "cathode rays".

For long scientists couldn't agree what the nature of that phenomenon was. Some were of the opinion that luminescence in the tube was caused by particles, and some other thought that cathode rays were of wave nature. The dispute between the first ones believing in the corpuscular model of cathode rays and the second ones in the wave model lasted up until 1896.

The one who put the stop to the dispute was an English scientist named Joseph John Thomson. In his experiment to produce cathode rays he used a tube filled with rarefied gas but he made a bit of modification with the equipment.
As it was said before cathode rays are emitted from the cathode and directed to the anode. What Thomson made with the equipment was a little gap in the anode. Through the gap a small beam of cathode rays got out of the area of the cathode and anode influence. Next, the beam passed through a long vacuum tube and fell on a fluoroscopic screen leaving there a fluorescent sign. In the vacuum tube Thomson put also two metal plates connected to a battery. That way he could create voltage between the plates, where the beam had its path. The field was directed perpendicularly to the cathode rays beam. It emerged that under the influence of voltage the beam was deflected (the spot on the screen appeared in a different place than without the voltage turned on). It was the final evidence that cathode rays consisted of charged particles- the other way the beam couldn't be deflected by the electric field. The direction of the deflection has shown of what charge the particles creating the beam are. It emerged to be the negative charge.

Thomson conducted also a second experiment defining the proportion q/m. He turned the beam of cathode rays on a special collector. He assumed that the particles were transferring their charge and energy when hitting the collector and sticking to it. He measured the gathered charge using a very sensitive electrometer. The kinetic energy (the energy of movement) of the particles at the collector changed into thermal energy heating it. So the energy could have been measured with a very sensitive device called thermoelement and by measuring temperature. Knowing the temperature, the transferred charge, and the velocity calculated before Thomson could define the proportion of the charge to the mass of the particles of cathode rays.

In 1897 Joseph John Thomson published the results of his work. Soon the new particle was called the "electron". In his work published in1898 Thomson affirmed that electrons were parts of all atoms and that cathode rays were electrons separated from atoms. The idea of an indivisible atom failed. Indivisible became divisible. The first elementary particle was discovered. But there was one issue left - the mass and the charge of the electron were still unknown.