On Certain Types of Electric Discharge. 



217 



of whose sides are parallel to the tube, was used to produce 

 such a field, fig. 1. 



Fig-. 1. 



Rectangular 

 lo pump. *, 



> ,? / 



From ce//s 



^ From 

 induction coil 



Toce/'s^snsirtrf 



7. According to the theory previously worked out, this 

 usual electrodynamic action between currents will be 

 observable only when the discharge is in the form of a band, 

 the number of corpuscles in this case being equal to that of 

 positive ions. 



The present experiment, therefore, is in confirmation of 

 this theory. 



8. When the pressure is further reduced (*03 mm.) T x 

 shows fine striatory discharge. 



This tube thus does not at all show the band stage — which 

 alone is affected by a magnetic field — with the induction- 

 coil used in the above experiment. 



9. At this pressure, the discharge in T 2 is striatory but 

 the stride are thicker ; while in T 3 the positive column is 

 entirely absent, the cathode glow extending over the whole 

 length of the tube. 



10. It will be seen that the characteristic changes in these 

 discharge-tubes and the characteristic differences between the 

 three tubes arising from a difference in length correspond 

 to the peculiarities exhibited by the curves connecting pres- 

 sure and potential difference in them. 



Curve II, fig. 2, gives the relation between pressure and 

 potential difference in T 2 . 



11. In T 2 , at high pressure down to nearly 55 cm., the 

 showery stage is indicated by the curved line. From this 

 pressure to nearly 25 cm., the discharge is in the form of a 

 band. This is indicated by a straight portion in the curve. 

 The discharge behaves during this stage as an ordinary flexible 

 wire carrying current. As the pressure is further reduced, 

 the curve bends away from the line of pressure, the difference 

 of potential increasing enormously with decreased pressure, 

 when the pressure is lowered below 2 mm. 



In the case of T 3 , the first stage is absent, as well as the 

 first portion of the curve. (Curve I. fig. 2.) 



