Certain Types oj Electric Discharge. 221 



2, 3, 4 (fig. 5). Thus, it is seen that for the same E.M.F. in 

 the primary, the current as well as the character of the 

 discharge depend on the pressure. 



There is one feature of this phenomenon brought out by 

 these curves, which is worthy of notice. When the discharge 

 is in the form of a band (curve 1, fig. 5) (pressure 24 mm.). 



Fig-. 5. 



<5O0 SOO 600 



Current in deflections of the n&lvanomeber 



within a certain range, the current is proportional to the 

 E.M.F. of the primary. Now, according to Ohm's law, the 

 current in a wire circuit is proportional to the E.M.F. when 

 the circuit is open. As we may reasonably take the E.M.F. 

 of the secondary, when no discharge passes, proportional to 

 the E.M.F. in the primary, we conclude that the band 

 discharge satisfies the criterion of a current in a wire- 

 circuit, in respect of Ohm's law. This is of interest in view 

 of art. 6. 



18. When the striatory discharge (in tube T 2 ) is placed 

 in the centre of a rectangular coil carrying current, the 

 number of striae increases, and in the actual experiment they 

 become inclined to their original directions,' while as the 

 current is reversed, the inclination is reversed also. 



19. A tentative theory of these experimental results 

 (art. 18) may be given as follows : — 



The Faraday dark space is, as we have seen ("Electric 

 Discharge in a Transverse Magnetic Field," Philosophical 

 Magazine, July 1916), a region practically devoid of ions. If 

 this is so, all the dark spaces in the striatory column must be 

 held to be also regions containing but few ions, and per 

 contra, the illuminated portions to mark regions where 

 there is copious ionization. 



20. A corpuscle being thrown off from the negative 

 electrodes will be in a condition to ionize the gas almost 

 directly, if the pressure of the gas in the tube is sufficiently 



