Passage of Electricity through Gases. 183 



a. Resistance of the positive discharge. — If two tubes of 

 different lengths are blown on to a glass globe containing the 

 negative electrode, and if at the ends of the tubes two similar 

 wires are placed as positive electrodes, and if the current of 

 induction is passed first through the long tube and then 

 through the shorter, the intensity of the current appears 

 greater in the latter case, because, in consequence of the 

 greater mutual influence of the electrodes on one another, a 

 smaller body of electricity is necessary to produce the tension 

 requisite for a discharge ; the discharge begins earlier, and 

 lasts longer. If, however, in the latter case the flow of 

 electricity, is retarded by the insertion of, e. g., a capillary tube 

 with a solution of sulphate of zinc, the discharge again ceases 

 sooner, and the same intensity of current may be obtained as 

 in the longer tube. The resistance of the solution in the 

 capillary tube does not, however, as argued above, directly 

 correspond with the difference of the resistance in the two 

 glass arms. 



If in this experiment the rarefaction of the gas be carried 

 still further, the induction-coil will continue to discharge 

 itself, even when the tension has fallen below that which was 

 necessary with a higher pressure ; the quantities of electricity 

 passing between the nearer electrodes become more equal to 

 those passing between the more distant ; and the resistance by 

 which the flow of electricity to the nearer electrodes may be 

 retarded, must be less in order to reestablish a complete equa- 

 lity. The phenomenon is therefore outwardly the same as if 

 the resistance of the positive discharge decreased. In the same 

 way, if the electromotive force of the induced current be more 

 powerful, e. g. if a stronger inducing current is employed, or 

 if the interruption of it be more rapid, the quantity of 

 electricity initially flowing to the electrodes will be greater, 

 the electricities flowing back to the coil after the discharge 

 will be less, in proportion to the whole ; and the resistance 

 of the positive discharge will appear, both by measurement 

 and by the above-mentioned experiments, to be less. 



b. Resistance at both electrodes. — According to Hittorf, if 

 the current is divided between two tubes of equal diameter, 

 but having the electrodes at different distances from one 

 another, the intensity in the two branches approaches equality 

 as the rarefaction is carried further. As in this case the 

 length of the positive discharge varies, Hittorf concludes that 

 the resistance of the former is small compared with that 

 around the negative electrode. It was mentioned at an 

 earlier part of this paper that the greater the rarefaction the 

 smaller the charge on the electrodes necessary for the com- 



