But then Crookes showed that a magnet would cause cathode rays
to curve in their path, and from the manner of curving, it seemed quite certain that they carried a negative electric charge.
He placed certain chemicals, known to fluoresce easily, inside a cathode ray
tube, surrounded it by dark paper, and darkened the room to observe the pale fluorescence that would result.
Hertz, the discoverer of radio waves (see 1888), had found that cathode rays
could pass through thin sheets of metal, and this seemed to favor their being a wave form.
From the amount of the deflection, Thomson could work out the ratio of the electric charge of the cathode ray
particle to its mass.
As physicists began to study the speeding electrons involved in cathode rays
, and in other phenomena, however, it turned out that electrons might be moving at respectable fractions of the speed of light-up to 90 percent in some cases.