Crookes Railway tube

You may have heard of a Crookes Radiometer, but this is the rarer Crookes Railway or Tramline tube and works in a totally different way. When invented in the 1800s by William Crookes it was thought to show that cathode rays had a particular nature with mass and momentum. While that may be true to some extent, they don’t have enough momentum to move the paddle wheel along the tube as show here. Note; this tube has fluorescent paint at the mica wheel blade tips and this is glowing under the electron bombardment. It was later understood the movement is caused by the much heavier charged ions in the tube due to the vacuum being imperfect. This is a genuine old tube and has quite a high vacuum, so is shown here operating with 30kV between the two electrode cups. At this potential the tube does emit some x-rays so is rarely demonstrated and probably not really suitable for public or school demonstrations. I have also added a video of the operation HERE .