166 



Prof. G. Wiedemann on the Laws of the 



towards the vertex, but it extended to the negative electrode 

 without being divided from it by any dark space. 



On putting the negative electrode to earth, the appearance 

 was but slightly altered ; only the bright part was advanced a 

 little, and the discharge was wider. On putting the positive 

 electricity of the machine to earth, another, darker spot ap- 

 peared at the positive electrode ; the dark space at the nega- 

 tive electrode was hardly perceptible. With a very small air- 

 spark and somewhat higher pressure of gas the discharge merely 

 passed between the ends of the electrodes in an arc, and was 

 scarcely altered by the interposition of a column of water. 

 The charging of the sides of the tube with free electricity is 

 seen by the following Table : — 



Electrode. 



Circuit unbroken. 



Air -spark at the 

 -j- electrode. 



Air-spark at the 

 — electrode. 



Insulated 



-f- put to earth... 



— put to earth... 



Whole tube — . 

 Diminishing +. 



Diminishing — . 



Whole tube — di- 

 minishing from 

 — electrode. 



Greatly diminish- 

 ing -. 



Weak + at the + 

 electrode, other- 

 wise almost un- 

 electric. 



Whole tube + di- 

 minishing from 

 -+- electrode. 



Weak — at the — 

 electrode,other- 

 wise almost un- 

 electric. 



Greatly diminish- 

 ing -f. 



With regard to the passage of electricity through gases, two 

 opinions have been put forward. On the one hand it was 

 supposed (and the opinion was suggested as the more probable 

 in the former memoir on the subject) that the particles of gas 

 situated at the electrodes carry with them the electricity at 

 the commencement of the discharge, and transmit the dis- 

 charge from one electrode to the other by means of a directly 

 progressive movement of the particles. Against this view 

 various physicists, and among them A. de la Rive, maintain 

 "that in gases of a certain density the discharge is indeed 

 disruptive, and therefore that gas, like every insulating body, 

 whether solid or fluid, plays the essentially passive part of a 

 hindrance to the re-connexion of the two electrodes, which, so 

 to speak, is mechanically overcome by the discharge. On the 

 other hand, gas of a certain density or rarefaction will allow 

 the electricity to flow out without mechanical resistance, and 

 will only offer an electrical resistance, while the transmission 

 of electricity takes place by so rapid a sequence of molecular 



