Through the 18th century, scientists had been fascinated by the
properties of electricity. Electricity seemed, at the time, to be a very
fine fluid that could extend through ordinary matter without taking up
any room.
Electricity did more than radiate through matter, however. It also
produced important changes in matter. In the first years of the 19th
century, it was found that a current of electricity could cause
different atoms or different groups of atoms to move in opposite
directions through a liquid in which they were dissolved.
The English scientist Michael Faraday (1791-1867) noted in 1832 that a
given quantity of electricity seemed to liberate the same number of
atoms of a variety of different elements. In some cases, though, it
liberated just half the expected number of atoms; or even, in a few
cases, just a third.
Scientists began to speculate that electricity, like matter, might
consist of tiny units. When electricity broke up a molecule, perhaps a
unit of electricity attached itself to each atom. In that case, the same
quantity of electricity, containing the same number of units, would
liberate the same number of atoms.
In the case of some elements, each atom could attach 2 units of
electricity to itself, or perhaps even 3. When that happened a given
quantity of electricity would liberate only one-half, or only one-third,
the usual number of atoms. (Thus, 18 units of electricity would liberate
18 atoms if distributed 1 to an atom; only 9 atoms if distributed 2 to
an atom; and only 6 atoms if distributed 3 to an atom.)
It was understood at the time that electricity existed in two varieties,
which were called positive and negative. It appeared that if an atom
attached a positive unit of electricity to itself it would be pulled in
one direction through the solution by the voltage. If it attached a
negative unit of electricity to itself it would be pulled in the other
direction.
[Illustration: _Michael Faraday_]
The units of electricity were a great deal more difficult to study than
the atomic units of matter, and throughout the 19th century they
remained elusive. In 1891, though, the Irish physicist George Johnstone
Stoney (1826-1911) suggested that the supposed unit of electricity be
given a name at least. He called the unit an “electron”.