406 Mr Rutherford, The Discharge of [Feb. 21, 



Experiment 3. Discharging power of a metal tube. 



If the aluminium tube T which was 30 cm. long and 1*1 cm. 

 diameter was connected to the electrometer and the central wire 

 removed, it was found that the gas gave up part of its charge to 

 the tube in its passage along it. In an experiment where the 

 velocity of the air along the tube was about 150 cm. per sec, £ of 

 the gas was discharged in passing along the tube. Since the 

 electrified particles tend to repel one another to the side such a 

 discharge is to be expected. If the volume density of the 

 electrification were uniform over the cross section of the tube, 

 an experiment of this kind on the discharging power would allow 

 us to calculate the velocity with which the carrier moves under 

 its own repulsion, but this condition is here not fulfilled. 



Experiment 4. 



All the electrification blown out between the electrodes C and 

 B can be collected. In one experiment the rate of leak of C was 

 observed with the blast in action. Part (1) of the charge which 

 left G was given up to the gauze B, a part (2) was discharged on 

 the tube T and the part (3) which escaped was caught in a cotton- 

 wool collector. The sums of the rates of leak to (1), (2) and (3) 

 were found to be very nearly equal to the rate of leak of G. 



Velocity of the Carrier. 



The general experiments on the effects of a current of air 

 between two electrodes when the ultra-violet light is acting may 

 be simply explained by supposing that the negatively charged 

 particles, which escape from the surface G, travel towards the 

 gauze B with a velocity proportional to the electromotive force 

 between the two plates. 



Let u = velocity of the charged particle for a potential gradient 

 of 1 volt per cm., 



d = distance between the plates, 



I = length of the plates, 



v = difference of potential in volts between the plates. 



The time t taken for the carrier to pass from one plate to the 

 other is therefore given by 



/ — - — ^ 2 



v uv ' 

 u . i 

 a 



