plates to either side of the cathode ray beam, a crude CRT. If the cathode rays were charged particles, their path should be bent by the electric field created when a voltage was applied to the plates, causing the spot of light where the rays hit to move sideways. He did not find any bending, but it was later determined that his tube was insufficiently evacuated, causing accumulations of surface charge which masked the electric field. Later Arthur Shuster repeated the experiment with a higher vacuum. He found that the rays were attracted toward a positively charged plate and repelled by a negative one, bending the beam. This was evidence they were negatively charged, and therefore not electromagnetic waves. Deflection by magnetic fields Crookes put a magnet across the neck of the tube, so that the North pole was on one side of the beam and the South pole was on the other, and the beam travelled through the magnetic field between them. The beam was bent down, perpendicular to the magnetic field. To reveal the path of the beam, Crookes invented a tube (see pictures) with a cardboard screen with a phosphor coating down the length of the tube, at a slight angle so the electrons would strike the phosphor along its length, making a glowing line on the screen. The line could be seen to bend up or down in a transverse magnetic field. This effect (now called the Lorentz force) was similar to the behavior of electric currents in an electric motor and showed that the cathode rays obeyed Faraday's law of induction like currents in wires. Both electric and magnetic deflection were evidence for the particle theory, because electric and magnetic fields have no effect on a beam of light waves. Paddlewheel Crookes put a tiny vaned turbine or paddlewheel in the path of the cathode rays, and found that it rotated when the rays hit it. The paddlewheel turned in a direction away from the cathode side of the tube, suggesting that the force of the cathode rays striking the paddles was causing the rotation. Crookes concluded at the time that this showed that cathode rays had momentum, so the rays were likely matter particles. However, later it was concluded that the paddle wheel turned not due to the momentum of the particles (or electrons) hitting the paddle wheel but due to the radiometric effect.