450 Mr. J. Henry on the Deflexion by Magnetic 



Experiments in Blowing the Discharge in a Rarefied Gas. 



Experiments were made to see if the discharge in hydrogen, 

 at pressures less than atmospheric, could not be blown aside, 

 as it was in other gases by the convection-currents in them 

 due to the heat of the discharge. 



For this purpose the tube shown in fig. 19 was employed. 



Fig. 19. 



X X 



T 



The discharge passed across the tube between the aluminium 

 electrodes a and b ; the diameter of the tube was 2*5 centim., 

 and the ends of the tube were drawn out, so that rubber 

 pressure-tubing could be slipped on them ; in this way the 

 end c of the tube was connected through a stop-cock k (not 

 shown in fig.) to a large vessel- A of 204:5 cub. centim. capacity, 

 and the end d to a large vessel B, and to the air-pump and 

 manometer. 



To begin an experiment the tube and vessels connected 

 with it were filled with the gas to be experimented with, then 

 the stop-cock k was closed and the gas pumped out of the tube 

 and vessel B. 



A current of gas could now be blown across the electrodes 

 by opening the stop-cock k, the strength of the blast depend- 

 ing on the difference of pressures between the gas in A and 

 that in B. 



In this way the discharge in air or carbonic acid gas could 

 be blown aside very readily when the pressure of the gas in 

 the tube was not high enough to make the discharge pass as 

 a bright sharp spark. By partially exhausting A, and then 

 further exhausting B, the mean pressure of the gas in the 

 discharge-tube while the blast through it lasted could be varied 

 at pleasure. 



When the gas used was hydrogen, the blast across the elec- 

 trodes when the stop-cock k was opened bent the discharge 

 very slightly for any pressure of the gas in the discharge- 

 tube. A strong blast had less effect than a rather gentle one : 

 cf. the blowing out of an arc mentioned above. 



By filling the vessel A and the tube with gas, vessel B 

 being cut off, and then steadily pumping, the stop-cock k 



