182 Prof. G. Wiedemann on the Laics of the 



from the point where the discharge has begun, even when the 

 charge on the electrodes does not attain its former density. In 

 this manner the discharge of the induction-coil may last a 

 shorter or longer time. The quantity of electricity passing 

 through the tube is greater or less in proportion to the rapi- 

 dity with which the electric density decreases at the electrodes, 

 while at the same time the discharge is gradually checked by 

 the flow of the denser air at the sides. When this electric 

 density has fallen to a certain amount the discharge ceases, 

 and the remainder of the electricities neutralize themselves 

 backwards through the coil. The construction of the coil itself, 

 the insertion of resistance between its terminals and the tube, 

 which tend to prolong the period during which the accumu- 

 lation of electricity lasts, an increase of the surface of the 

 conductors by conclensing-plates or other means, may each 

 materially influence the quantity of electricity passing through 

 the tubes. 



If a galvanometer be inserted in the circuit, or in a branch 

 of it, the deviation measures directly or indirectly the quantity 

 of electricity which has passed through the tube — i. e. the 

 quantity which flowed to its electrodes, less that which flowed 

 back into the coil. If the electrodes be connected direct, and 

 the deviation of the galvanometer observed, or if the tube be 

 replaced by a rheostat so as to make the deviation the same 

 as before, the backward flow (alternate discharges apart) does 

 not take place. In the first experiment the antecedent elec- 

 trostatic relations exercise an ^influence on the quantity of 

 electricity carried over in the discharge, while in the second 

 the flow of the electricity actually set in motion is the only 

 quantity concerned. The two experiments, therefore, take 

 place under quite different conditions ; so that the resistance 

 of the tube cannot be determined by a comparison of the 

 results*. Nor, indeed, can it be effected by connecting 

 a galvanometer with different points of the conductors, so as 

 always to produce the same deviation under various conditions 

 of current and tube |. 



We therefore have to examine in what relations the results 

 already obtained, as to the supposed resistance of the separate 

 parts of the discharge, stand with regard to the conditions of 

 the discharge in general ; and for this purpose we return more 

 particularly to the beautiful experiments of Hittorf J, from 

 which we will select the simplest. 



* Morren ; cf. Galvanismus (2). Bd. ii. S. 951. 



f A. de la Rive; cf. Galvanismus (2), Bd. ii. S. 952, 953. 



X Cf. Galvanismus (2), Bd. ii. S. 958. 



