354 M. E. Goldstein 07i Electric Discharges 



from the positive towards the negative pole^ the properties aro 

 those of the so-called positive light. If, on the other hand, 

 a rapid diminntion of cross section takes place in the direction 

 of the current, the discharge at that point will have all the pro- 

 perties of the negative light. The more rapid this diminntion 

 is, the more like a negative light will the discharge ap})ear. 

 By varying in different ways the cross section, we can form 

 the intermediate stages between the positive and negative light. 



3. Between the dark space and the negative pole we always 

 see the negative light. 



In a series of experiments it appeared as if the passage of 

 electricity from the electrode to the gas took place through a 

 series of fine pores. Without putting forward any hypothesis, 

 I merely draw attention to this fact in order to show that my 

 statement^ as to the variation in cross section being the pri- 

 mary cause of the distinction between the two discharges, is 

 not in disagreement with the appearance of the negative light 

 at the negative pole. 



The distinction which has been drawn between the two 

 parts of the discharge which lie on either side of the dark space 

 took its origin in the difference between their optical and 

 magnetic properties. 



4. A large number of observers agree in the statement that 

 the spectrum of a gas at the negative pole is different from 

 that of the positive discharge. Such differences seem to have 

 been made out with certainty in the case of nitrogen and hy- 

 drogen. 



Experimenting with these gases, I succeeded in changing the 

 spectrum of the positive discharge into- that of the negative 

 light, either by great exhaustion or by an increase in the in- 

 tensity of discharge. 



5. The observations of Eeitlinger and Kuhn, '^ On Spectra 

 of Negative Electrodes and of Geissler Tubes which have been 

 used for a long time" (Pogg. Ann. vol. cxli.) are entirely ex- 

 plained by the fact that the gas, owing to the long-continued 

 discharge, was absorbed by the electrodes. Owing to the great 

 exhaustion thus obtained, the spectrum of the negative pole 

 was seen throughout the tube. 



I have often found tubes which gradually absorb the gas 

 contained in them ; and I have now some in my possession, in 

 which I can at pleasure produce the phenomena either of 

 great exhaustion or of high pressure. By heating up the elec- 

 trodes from outside, the gas is driven out of the electrode and 

 the pressure increased. The passage of the currents, however, 

 soon causes the reabsorption of the gas, and consequently the 

 phenomena of great exhaustion appear again. 



