Transmission of Electric Disturbances. 



139 



variable the strise may be of slightly different lengths, and 

 (2) will only be approximately true; the accurate equation 

 will be 



t=K + „0. 



According to this view the discharge takes place when 

 the value of the potential difference has the value given 

 by either (1) or (2) and not when the maximum electro- 

 motive intensity has a certain value. Dr. Schuster's reduction 

 of Bailie's and Paschen''s experiments shows that the maxi- 

 mum electromotive intensity when the spark passes is by no 

 means constant. 



If by the combination of the atoms at the end of a stria 

 sufficient heat is produced to dissociate the adjacent gas without 

 the aid of the electric field, the gas dissociated will, as the ex- 

 periments I described in the Philosophical Magazine for April 

 and May 1890 prove, be able to conduct the electricity, even 

 though the potential difference is very small. We should 

 then have a region in the gas where the potential charges are 

 small compared with those in other parts of the gas : the 

 dark space between the negative glow and the positive column 

 seems to be such a region, and it is situated near to the 

 negative glow, the hottest part of the field. 



When the dimensions of the electrodes are not large com- 

 pared with the sparking-distance, the connexion between the 

 sparking -distance and the difference of potential is not linear. 

 The experiments of De La Rue, Hugo Miiller, and Freiberg 

 have shown that with pointed electrodes, or small spheres, 

 the sparking-distance for the same difference of potential is 

 greater than with larger electrodes. This is what we should 

 expect from the preceding considerations, for according to 

 them when the spark passes from the negative electrode the 



distribution of potential must be represented by the straight 

 line AB, where the abscissae represent the distance from the 



