254 The Outline of Science 



some fundamental matter of which the various atoms were com- 

 posed one primordial substance from which all the varying 

 forms of matter have been evolved or built up. Prout suggested 

 this at the very beginning of the century, when atoms were redis- 

 covered by Dalton. Father Secchi, the famous Jesuit astronomer 

 said that all the atoms were probably evolved from ether; and this 

 was a very favoured speculation. Sir William Crookes talked 

 of "prothyl" as the fundamental substance. Others thought hy- 

 drogen was the stuff out of which all the other atoms were 

 composed. 



The work which finally resulted in the discovery of radium 

 began with some beautiful experiments of Professor (later Sir 

 William) Crookes in the eighties. 



It had been noticed in 1869 that a strange colouring was 

 caused when an electric charge was sent through a vacuum tube 

 the walls of the glass tube began to glow with a greenish phos- 

 phorescence. A vacuum tube is one from which nearly all the 

 air has been pumped, although we can never completely empty 

 the tube. Crookes used such ingenious methods that he reduced 

 the gas in his tubes until it was twenty million times thinner than 

 the atmosphere. He then sent an electric discharge through, and 

 got very remarkable results. The negative pole of the electric 

 current (the "cathode") gave off rays which faintly lit the mole- 

 cules of the thin gas in the tube, and caused a pretty fluorescence 

 on the glass walls of the tube. What were these Rays? Crookes 

 at first thought they corresponded to a "new or fourth state of 

 matter." Hitherto we had only been familiar with matter in the 

 three conditions of solid, liquid, and gaseous. 



Now Crookes really had the great secret under his eyes. But 

 about twenty years elapsed before the true nature of these rays 

 was finally and independently established by various experiments. 

 The experiments proved "that the rays consisted of a stream of 

 negatively charged particles travelling with enormous velocities 

 from 10,000 to 100,000 miles a second. In addition, it was found 



