134 On the Production of the iv-JRays by a Battery (Jurreni. 



until a difference of potential competent to produce a spark 

 in air of an inch excited the #-rays with great brilliancy; at 

 the same time a difference of potential giving a spark of 

 eight inches could not produce these rays in the other con- 

 necting tube ; the same degree of vacuum, so to speak, 

 existed in both tubes. The phenomenon of the occlusion of 

 gases seems to be the controlling one in the production of the 

 rays, and not the degree of exhaustion. With the steady 

 battery-current one can watch this phenomenon to great ad- 

 vantage. When the tube is heated to a certain critical tem- 

 perature a blue cloud proceeds from the anode, and is met 

 by the cathode-beam from the cathode. If the strength of 

 the current is then gradually increased by diminishing the 

 resistance in the circuit, this blue cloud fills the entire tube : 

 the anticathode grows white hot and the #-rays cease to 

 appear. When the current is diminished the anticathode 

 sinks to a cherry-red, the blue cloud contracts and sinks into 

 the anode, and the #-rays come out with great brilliancy. 

 The disappearance of the blue cloud betokens a rise of re- 

 sistance in the tube ; for the glow on the anticathode grows 

 less and less, and presently, if the current is not increased, 

 the tube is completely extinguished and a reheating is 

 necessary. 



A steady battery-current with an adjustable liquid re- 

 sistance is indispensable, I believe, if we wish to study the 

 best conditions for producing the rays. A storage-battery of 

 forty thousand volts enables me to try a wide range of voltage 

 and current strength ; moreover, the radiant point of the rays 

 is less likely to produce ghosts. The tubes appear to glow 

 in a perfectly steady way, and the degree of excitation of the 

 rays seems to be under perfect control. The phenomenon of 

 occlusion in an #-ray tube having such an important bearing 

 on the subject of the passage of gases through a rarefied 

 space, I was interested to trace the phenomenon from a pres- 

 sure of one or two millimetres up to the a'-ray stage. I 

 used for this purpose an end-on tube of a peculiar construc- 

 tion. One end of the tube was blown out into a thin bulb 

 through which the #-rays could be observed. It was possible 

 to heat this tube strongly so as to produce a high state of 

 exhaustion; and this form of tube was very useful in study- 

 ing the electrical discharges by a spectroscope. When the 

 tube was exhausted to the stratified discharge stage, and was 

 connected to the terminals of the battery, the intensity and 

 form of the stratifications could be changed by increasing or 

 diminishing the strength of the battery-current. When this 

 current was increased, a blue discharge in the form of a stra- 



