460 Pressure of the Electric Wind in Hydrogen. 



oxygen is followed by a stream of corpuscles travelling at 

 very high speeds from the negatively charged point, they may 

 travel considerable distances before settling down into the 

 state of ordinary negative wind-producing ions. Moreover 

 they will ionize the gas at these considerable distances. 

 Hence by the principles of both (i.) and (ii.) we may expect 

 large values of z on this view. 



Experiments now in contemplation on the effect on z of 

 changes in the discharging point should throw light on this 

 question. 



In this connexion it is worth while to recall the fact that the 

 state of the point has a very marked influence on the amount 

 of combination which occurs between oxygen and hydrogen 

 when the percentage of oxygen is low. For the four phe- 

 nomena of glow, fall of wind pressure, shift of negative curve, 

 and abnormally rapid combination all take place within about 

 the same narrow limits of oxygen percentage; and it is there- 

 fore at least tempting to think that they may all ultimately 

 prove traceable to a single source. 



Summary. 



1. The gradual removal of the last one per cent, of oxygen 

 from hydrogen gives rise to a marked fall in the electric wind 

 when a negative point discharges through the gas against a 

 plate. 



2. This fall is probably due to discharge of positive elec- 

 tricity from the plate, and may even amount to a slight 

 reversal of the wind in very pure hydrogen. 



3. The fall is accompanied by a glow upon the plate 

 which may be regarded as further evidence for such back 

 discharge. 



4. Within the same limits of percentage change of oxygen 

 the straight part of the negative wind pressure curves becomes 

 shifted parallel to itself through a distance which may amount 

 to 3 centimetres. It is suggested that this shift may be con- 

 nected with the growth of the ions from the corpuscular 

 magnitude to that of the ordinary negative ion. 



5. None of the above effects occur with positive discharge 

 in hydrogen, which is practically uninfluenced by the presence 

 of oxygen up to the highest percentage (3*7) used. 



In conclusion we wish to acknowledge our indebtedness to 

 the Royal Society for a grant in aid of this research. 



