Editing Cathode ray (section)

===Paddlewheel===
[[file:Crookes paddlewheel tube.png|thumb|Crookes's paddlewheel tube, from his 1879 paper ''On Radiant Matter'']]
[[William Crookes|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.<ref name="Thomson" />{{rp|146-149}} 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. [[William Crookes|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 [[Crookes radiometer|radiometric effect]].<ref name="Brona" />  When the rays hit the paddle surface they heated it, and the heat caused the gas next to it to expand, pushing the paddle. This was proven in 1903 by [[J. J. Thomson]] who calculated that the momentum of the electrons hitting the paddle wheel would only be sufficient to turn the wheel one revolution per minute.<ref name="Brona" /> All this experiment really showed was that cathode rays were able to heat surfaces.