162 Prof. G. Wiedemann on the Laws of the 



charge increases ivith the pressure, at first rapidly, then more 

 slowly and nearly in proportion to the increase of pressure. 

 These quantities of electricity are, under circumstances otherwise 

 similar, greater and greater for the following gases in order, 

 hydrogen, oxygen, carbonic acid, air, and nitrogen. 



From the difference of charge on the two electrodes neces- 

 sary for effecting a discharge, an explanation of the various 

 features of the discharge was deduced. 



On account of their greater potential, the gas-moiecules at 

 the positive electrode are repelled with a greater velocity than 

 those at the negative ; and consequently the positive discharge 

 extends to a greater distance from the positive electrode than 

 the negative from the negative. Further, since the difference 

 of tension at different points of an electrode is greater with 

 large than with small charges, the discharge from the positive 

 takes place only from the point directed towards the negative, 

 while that from the negative takes place more largely from 

 the general surface. When the discharge takes place between 

 a plate and a small sphere, we find at the meeting of the two 

 discharges phenomena similar to those produced at the meet- 

 ing of two currents of water. If the plate is negative, it ex- 

 hibits the glow or halo, while the positive discharge from the 

 sphere sinks in a cup-shape ; if the plate be positive, the red 

 positive discharge from it is raised towards the halo on the 

 sphere. 



Similarly we may find an explanation of the action of the 

 electric egg, and of the connexion between the direction and 

 velocity of the magnetic rotation of a discharge in rarefied air 

 (between a point and a ring) and the direction of the discharge. 



In the later experiments one of the spherical electrodes of 

 the vacuum-tube was connected with one conductor of the 

 Holtz machine, the other conductor of which was connected 

 with the earth, while the second electrode was connected with a 

 galvanometer and thence with the earth. Whether the first 

 electrode was charged with positive or with negative electri- 

 city, the alternating discharges, and consequently the quan- 

 tity of electricity passing through the tube, remained un- 

 changed. But still the number of discharges in a unit of 

 time was greater when the electricity drawn from the machine 

 was negative. 



The above-mentioned difference of quantity of positive and 

 negative electricity necessary for effecting a discharge is not 

 determined by the passage of unequal quantities through the 

 apparatus used for the discharge. The same result will be ob- 

 tained if a spectrum-tube, i. e. a capillary tube with spherical 



