Measuring the smallest unit of charge

It is strange how one thing leads to another. Today, the electron is an accepted fact of life. Even though nobody can vouch that he has seen an electron, scientists have not only found out all its behavioural properties, they have rallied around beams of electrons in CRTs and TV sets and harnessed their behaviour to the benefit of mankind in gadget after gadget.

Millikan However, before succumbing to the tyranny of human technology, the electron teased the scientific intellect for more than 200 years and lured scientists to come out of the Daltonian dogma of indivisibility of an atom.

The electrons – the free electrons, freed from the bondage of the nucleus, first made their presence felt in studies of passage of electricity through air. As far back as 1705, it had been noticed that sparks from an electrical machine would jump further in rarefied air than in air at normal pressures. As early as 1748, it was observed that an aurora borealis-like arch flew in a 32 inches long glass tube of rarefied air.

These were spectacular sights. But nobody knew what caused the spectacle. It was like a genie in the bottle.

In 1838, Michael Faraday sent a current from an electrostatic machine through a glass tube containing air at low pressure and observed a purple glow extending from the positive electrode (anode) at one end almost to the cathode at the other end. The cathode was covered with a glow and there was dark space between the glow and the purple column. The dark space has since been called Faraday Dark Space. Some speculated on the existence of electroplasm – the stuff that ghosts are supposed to be made of.

The studies of electrical discharge through gases continued in Germany with improved vacuum technology. It was concluded that the luminescent glow on the tube was caused by “rays” originating at the cathode. Nobody understood what these “rays” were, but they were deflected by a magnet and were able to cast the shadow of an obstacle placed in their path. So they travelled in straight lines, just like light. Goldstein called these mysterious rays ‘cathode rays’.

Robert A Millikan

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