256 Mr M c Clelland, On the Conductivity of Gases 



positive electricity can be discharged a further heating of some 

 400 degrees centigrade is required. 



It is intended to make further and more accurate experiments 

 on these points. 



Incandescent Wire in Air. Velocity of Carriers. 



(26) Experiments were made to determine the velocity of 

 the carriers under 1 electric force in the same way as when the arc 

 was used. With the incandescent wire, as with the arc, it was 

 found that the velocity of the carrier varied as the temperature of 

 the wire changed ; the higher the temperature of the wire the 

 smaller was the velocity of the carrier. In one set of experiments 

 values were found ranging from "01 cms. per second to '008 cms. 

 per second. When the arc was used values of the velocity of the 

 carriers were found lying inside these limits, but when the currents 

 through the arc is small the velocity of the carrier is greater than 

 any value found when using the incandescent wire. The diminu- 

 tion of the velocity with increase of current in the arc would seem 

 to be due to the heating of the terminals, and not to anything 

 that occurs in the arc itself. The same effect is then produced by 

 an increase of temperature of the incandescent wire. 



The velocity of the negative carrier is greater than that of the 

 positive when the incandescent wire is used, and the excess is 

 about 20 °/ , the same as for the arc. 



Incandescent Wire in C0 2 . 



(27) The effects observed with C0 2 were similar to those 

 with air. It will be remembered that when an arc was formed 

 in C0 2 , the gas from it discharged negative electricity much more 

 rapidly than positive ; it was difficult to get the negative carriers 

 away from the arc. The incandescent wire was tried in C0 2 to 

 see if a similar effect occurred, but it was found that when the 

 temperature of the wire was sufficiently high the gas from it 

 discharged positive electricity as rapidly as negative. The cause 

 assigned for the discharge of the negative carriers to the terminals 

 of the arc would not apply to the incandescent wire where there 

 is a very small electric field, all parts of the wire being nearly at 

 zero potential. We give some numbers referring to the conduc- 

 tivity observed with a wire heated in C0 2 . 



Current heating Leakage 



the wire Positive change Negative change 



44 amperes No leak No leak 



5*4 amperes No leak 30 divisions in 60" 



6"4 amperes No leak 45 divisions in 60" 



7'4 amperes 4 divisions in 60" 62 divisions in 60" 



8'4 amperes 100 divisions in 28" 100 divisions in 28" 



