the Hot Gases from Flames. 



37 



water, the water escaping by b and the air by a. It is kept 

 so during an experiment ; then by closing a, and taking the 

 time in which the level of the water in V sinks through a 



Fig. 5. 



short distance, and knowing the cross-section of V, we get 

 the volume of air drawn through A in a given time. Knowing 

 the cross-section of A, and also the temperature inside it at 

 any point, we get the velocity of the current of gas through 

 A at that point. The temperature is determined by pulling 

 out the plug of ebonite and inserting a thermometer. 



A is connected to earth and C is charged by storage-cells, 

 and the rate of leak measured as described previously. C is 

 charged sufficiently high to ensure that the gas is completely 

 discharged in passing it. The rate of leak of C is thus 

 determined (1) when B is connected to earth, (2) when B is 

 charged to such a potential that the rate of leak from C is 

 about halved. These two determinations enable us to calcu- 

 late the velocity of the carriers. The carriers of opposite sign 

 to B in a part of the cross-section of the tube are discharged 

 to B ; the area thus discharged is given, as we have seen 

 above, by 



t= 



1 p'-r « 

 vY 2 





where the letters denote the same quantities as before. We 

 can determine p from the rate of leak of C in the two cases 



