English: Cathode rays in magnetic field. (Crookes tube; B ≠ 0) A Crookes tube demonstrating deflection of cathode rays by a magnetic field. The electrode at the rear of the tube is the cathode, while the anode is in the glass neck at the base of the tube. A high voltage of several kilovolts is applied between the electrodes, creating positive ions in the residual gas in the tube which strike the cathode, releasing electrons. The electrons, attracted by the anode travel to the front of the tube and hit the glass wall, causing it to fluoresce (glow) with green light. The metal cross in the tube blocks the electrons, casting a shadow on the glowing wall. The poles of the magnet create a magnetic field horizontally through the neck of the tube. The electron beam passes through this field and is bent downward, so it only hits the bottom of the front wall.