6 Sir Oliver Lodge on the Mode of Conduction in Gases 



3. Next test. The tap was opened so as to enable 

 the current to pass by the supplementary path. If now 

 A is made negative and B positive, cathode rays emanate 

 from all parts of the rod A and drive along both the vertical 

 and the horizontal tube. The resistance at high vacuum is 

 therefore very great, and there is practically no positive glow 

 visible. 



4. The connexions were now reversed, so that A was 

 positive and B negative. Cathode rays are now manifest 

 and plentiful in the bulb outside the spiral, whereas few or 

 none are perceived at the bottom of the spiral, and no strain 

 is there noticeable. In fact everything is easy, and there is 

 very little heating effect. The luminous glow is strong in 

 the vertical part of the tube between the rod A and the spiral, 

 and inside the spiral : it is also visible, though rather weak, 

 along the supplementary path. The resistance of the tube 

 thus arranged is low, it conveys a considerable current 

 easily. It is in fact evident that the main current travels 

 upward fairly freely from rod A ; the bombardment opposed 

 to it being considerablv relieved bv the fact that negative 

 projectiles from the sides of the spiral are now possible, 

 owing to the positive carriers which come along the supple- 

 mentary path in sufficient quantity. The constant supply of 

 such positive carriers is presumably assisted by the driving 

 down of neutral atoms towards the anode, whence they can 

 pass through the constricted space round it, can enter the 

 little bulb and so make their way up the supplemental path 

 through the tap, as required. 



Comment. 



If it be asked how it happens that the bombarding electrons 

 convey so little current, though their mechanical effort is so 

 energetic, the first answer that suggests itself is that it is 

 because their velocity is so high, approximating to the order 

 of the velocity of light. The slow moving positive charges 

 would seem likely to have but little kinetic energy, though 

 they can convey much current ; the quickly flying electrons 

 would be in the opposite plight. 



The mechanical energy depends upon nmu 2 , the current 

 conveying capacity upon neu. Hence sufficient carriers at 

 low speed would be effective conveyers of current, though 

 without energy enough to progress in the teeth of projectiles 

 moving at anything like the velocity of light. 



But considering the matter further, it can be argued that 

 the positive carriers must sooner or later be all neutralized by 

 meeting an electron ; wherefore in the last resort the total 



