380 



De La Rue and Muller. 



[May 16, 



resistance of the tube, but that this increase depends more upon the 

 smallness of the diameter of the constricture than upon its length. 



Fig. 5. 

 TUBE 154- 



C 1 i> 



TUBE 155 



t~ r~-t- h> 



In the course of our experiments we have arrived at the following* 

 facts : — 



1. The discharge in a vacuum tube does not differ essentially from that 

 In air and other gases at ordinary atmospheric pressures ; it cannot be 

 considered as a current in the ordinary acceptation of the term, but must 

 be of the nature of a disruptive discharge, the molecules of the gas acting 

 as carriers of electrification. The gases in all probability receive two im- 

 pulses in opposite directions^ that from the negative being the more con- 

 tinuous of the tivo* Metal is frequently carried from the terminals and is 

 deposited on the inside of the tube, so as to leave a permanent record of the 

 spaces between the strata. 



2. As the exhaustion proceeds the potential necessary to cause a current 

 to pass diminishes up to a certain point, whence it again increases, and 

 the strata thicken and diminish in number, until a point is reached at 

 which, notwithstanding the high electromotive force available, no discharge 

 through the residual gas can be detected. 



3. All strata have their origin at the positive pole. Thus, in a given 

 tube, with a certain gas, there is produced at a certain pressure, in 

 the first instance, only one luminosity which forms on the positive 

 terminal, then, as the exhaustion is gradually carried further it 

 detaches itself, moving towards the negative, and being followed by 

 other luminosities, which gradually increase in number up to a certain 

 point. 



4. With the same potential the phenomena, vary irregularly with the 

 amount of current. Sometimes, as the current is increased, the number 

 of strata in certain tubes increases, and as it is diminished their 

 number decreases ; but with other tubes the number of strata fre- 

 quently increases with a diminution of current. 



5. A change of current frequently produces an entire change in the 

 colour of the strata. For example, in a hydrogen tube from a cobalt 

 blue to a pink. It also changes the spectrum of the strata ; moreover, 

 the spectra of the illuminated terminals and the strata differ. 



6. If the discharge is irregular and the strata indistinct, an alteration 



* " Phil. Trans.," Part I, vol. clxix, pp. 90 and 118. 



