the Anode in)Vacuum-Tubes. 195 



cannot be got near enough to the anode to measure the 

 distance in which this voltage drop occurs. Now the mean 

 free path of an electron in oxygen at 3 mm. pressure is 

 about l'lxlO -2 cm., and as the potential gradient in the 

 positive column is small, the maximum energy that an 

 electron can acquire in moving up to the anode from a point 

 distant 1*4 x 10" 2 cm. is the energy o£ the anode fall at 

 most, i. e. a 20-volt energy. As the measured energy is 

 35 volts, a 15-volt energy must be accounted for in some 

 other way. 



Now a rough value of the potential gradient in the 

 positive column can be got from a knowledge of the cathode 

 fall, the anode fall, the potential across the tube, and the 

 distance between the electrodes. In the case considered, the 

 mean gradient in the positive column 



515-370 volt 

 10 cm. 



i K volt 



= 15 . 



cm. 



If, then, we assume that all the energy acquired by the 

 negative carriers in moving up to the anode from a distance 

 of 1 cm. is given up as heat, all the 35-volt energy is 

 accounted for. 



Now in 1 cm. at this pressure, a corpuscle makes about 

 50 collisions and an ion of molecular size about 200, so that 

 in spite of a great number of collisions energy is " accumu- 

 lated" by the negative carriers in some way and transferred 

 to the anode. It is not suggested that all the energy 

 acquired by the carriers within 1 cm. of the anode is trans- 

 ferred to the anode, and none from the positive column 

 beyond this distance. Probably the whole column of gas 

 up to the negative glow contributes to the 15-volt energy 

 not accounted for by the anode fall. 



II. Possibility of an "Accumulation " of Energy. 



The following considerations show the possibility of an 

 " accumulation " of energy by an ion in spite of frequent 

 collisions. 



One possibility — that ionization occurs on collision — may 

 be regarded as very improbable, because the gradient in 

 the positive column is small, 



A further possibility is that an aggregate ion or cluster is 

 formed on collision. There is abundant evidence to show 



02 



