1869-1875

Crookes tube

• A Crookes tube was a Geissler tube
• but with a better vacuum,
• and instead of demonstrating glowing discharges,
• a Crookes tube demonstrated cathode rays.
• The rays emanated, strangely,
• at a right angle to the cathode
• and travelled in a straight path toward the anode,
• unless, as Crookes showed,
• a magnetic field caused them to bend
• as though they carried a negative charge.

Electromagnetics

• Playing with a Crookes tube,
• Wilhelm Röntgen discovered rays
• that passed through opaque materials
• and called them X-rays.
• *
• Wondering what corpuscles could be shooting
• from cathode to anode of a Crookes tube,
• J. J. Thomson calculated their charge-to-mass ratio,
• showed their mass was about a thousandth of a hydrogen atom.
• George Francis FitzGerald argued
• that George Johnstone Stoney’s term
• for the standard unit of electricity, the electron,
• should name Thomson’s corpuscles.

Cathode ray vision

• Cathode rays, negatively charged,
• and can be deflected by a magnetic field
• or made to rapidly sweep side to side,
• top to bottom, to illuminate a test pattern
• on a phosphorous screen,
• or to bleep from eleven to three.