THE PATH OF EVOLUTION 



the fusion of the glass. Means are provided whereby 

 the air or other gas contained therein can be ex- 

 hausted to any desired extent ; if absolutely exhausted, 

 no electric current will pass. When the above-named 

 wires are connected with the terminals of a Ruhm- 

 korf 's or induction coil, whereby the rapid alternating 

 currents of magneto-electricity are produced, electric 

 sparks will pass through the partially exhausted tube 

 so frequently as to appear like a constant stream. 

 The wire by which the current enters the Anode 

 bears on its inner end a small concave Platinum disk. 

 The opposite wire the Kathode bears either a 

 similar disk or, if producing the Rontgen rays (the 

 X-rays), a small, flat plate, inclined at about an angle of 

 forty-five degrees toward one side of the tube. When 

 the aerial contents of the tube are so far exhausted 

 that only about one-millionth thereof remains, and 

 the alternating secondary electric current is passed, 

 the rosy light that first appears between the elec- 

 trodes gradually retreats towards the Anode and finally 

 disappears, whilst from the Kathode, the negative 

 pole, a pale, bluish light spreads in increasing volume, 

 and finally, though but faintly visible, fills the whole 

 tube. These Kathode rays pass in straight lines per- 

 pendicularly from the surface of the Kathode plate 

 without regard to the relative position of the two 

 poles. They can be deflected by a magnet bent out 



188 



