Autograph Letter Signed ‘William Crookes’, to Lord Avebury, accepting an invitation. 1 page 5 x 3 inches, in good condition, one minor blemish at left edge. 7 Kensington Park Gardens, 10 July 1903. Sir William Crookes, F.R.S. (1832-1919), physicist, inventor and chemist, discovered thalium (1861). In 1875 he invented the radiometer. Crookes’s name is preserved in his vacuum tubes. He did not invent the vacuum tube with a cathode and anode to produce an electric current, but his Crookes tubes were superior. With them he discovered the basic properties of the electric discharge, or cathode ray, from which J.J. Thomson was to discover the electron, confirming Crookes’s own views on the nature of cathode rays.