Was the ray a wave or a stream of matter?

Inside evacuated glass tubes, high voltage produced a green glow opposite the cathode. Many physicists treated cathode rays as a disturbance in ether; others suspected a stream of charged particles.

J. J. Thomson avoided arguing from appearance. He watched what traveled with the ray and how its path changed. When a magnetic field steered the glow into a collector, negative charge arrived with it. Better evacuation then allowed an electric field to bend the ray as well.

Crossed-field velocity selector Scientific model diagram + + − − − − E ↓ 2.00e4 V/m E ↓ 2.00e4 V/m B ⊗ 0.01 T · into page B ⊗ 0.01 T · into page Velocity selection Velocity selection qE + qv × B = 0 qE + qv × B = 0 v = E / B v = E / B E = 2.00e4 V/m E = 2.00e4 V/m B = 0.01 T B = 0.01 T v = 2.00e6 m/s v = 2.00e6 m/s |Fᴱ| = |Fᴮ| |Fᴱ| = |Fᴮ| 3.20e-15 N 3.20e-15 N Net force zero; straight through Net force zero; straight through v = 2.00e6 m/s v = 2.00e6 m/s Fᴱ = 3.20e-15 N Fᴱ = 3.20e-15 N Fᴮ = 3.20e-15 N Fᴮ = 3.20e-15 N
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Diagram description

Animated physics diagram: thomson_velocity_selector; showing time.

The ratio was far too large

Balancing electric and magnetic deflection let Thomson estimate the particles’ charge-to-mass ratio. It was far larger than that of any known ion. Either their charge was enormous or their mass was tiny.

The same result appeared with different gases and electrode materials. These “corpuscles,” later called electrons, were not peculiar fragments of one substance. They were components of every atom.

Atoms had carried a name meaning indivisible. A bent ray made that name obsolete.