f=l 



381 Action of Radium on the Electric Spark. 



capsule of the shape shown in fig. 4, and was placed near 

 enough to the spark to extinguish it. j?- 10 ^ 4 



The capsule was further placed between 

 the poles of a strong electromagnet, 

 so orientated that the ft rays would be 

 driven into the lead by its action. Imme- 

 diately the magnetic field was created, 

 the discharge passed again with un- 

 diminished intensity, while when the 

 current in the magnet was stopped the 

 visible discharge also stopped, showing 

 clearly that it was the easily deflectable 

 /3 part of the rays that was concerned in the extinction. 



As these rays are of the same nature as Lenard rays, the 

 action on the spark of the latter was also tried. With 

 the aluminium window of the tube distant from the spark 

 about 10 cms., an appreciable effect could he seen ; when the 

 tube was in good working order and the spark in its most 

 sensitive condition, extinction of the latter could be readily 

 brought about. If the cathode rays inside the tube were 

 deflected from the window by means of a magnet, so that no 

 Lenard rays existed outside, no action on the spark could be 

 seen. In fact the discharge from the Wimshurst could 

 be started and stopped quite readily by simply approaching 

 a magnet to the cathode of the Lenard tube. 



The ionizing action of the rays as tested by an electroscope 

 10 cms. away from the window, was more than that of the 

 radium 50 cms. away, but less than that of the Rontgen rays 

 when the tube emitting the latter was 25 cms. away. 



This experiment also shows that the failure of the Rontgen 

 rays to put out the spark cannot be ascribed to their 

 intermittence, as both Lenard and Rontgen tubes were 

 worked by the same coil. It would also tend to prove that 

 the effects are dependent on the high velocity of the /3 rays, 

 rather than directly on the number of ions they produce in 

 the gap ; for the ionization produced by the Lenard rays is 

 here greater than that produced b}^ the radium, while it 

 is well known that their velocity is much less than that of 

 the ft rays that the radium emits. 



In conclusion we must express our gratitude to Mr. J. J. 

 Yezey for the loan of some radium bromide, with which the 

 preliminary experiments were performed, and also to the 

 Governors and Principal of the Institute for providing us 

 with the radium bromide necessary to continue those ex- 

 periments. We are also indebted to Mr. F. G. Bratt for 

 considerable help in the experimental part of the investigation. 



Sir John Cass Technical Institute, Jewry St., E.C. 

 November 10, 1904. 



