1045 



is proportional to the supplied energy. 4. As to the pressure of the 

 gas the following conclusions are drawn from the measurements. 



a. For constant current density (he intensity of the light decreases 

 with a decrease of the pressure for the investigated range of pressure. 



h. At the same time the maximum of the emitted energy is 

 shifted towards the shorter wave-lengths. 



c. At a change of the pressure of the gas the bands belonging to 

 the negative pole show a characteristic difference in behaviour with 

 the bands of the second positive nitrogen group which surround them. 



(I. The potential gradient in the positive column decreases with 

 decrease of pressure and also with increase of intensity of the current. 



e. At the side of the cathode the passage of a current gives rise 

 to a decrease in pressure, which for high values of the current 

 density is relatively great; the value of this pressure effect proves 

 to be (approximately) proportional to the intensity of the current. 

 This effect is opposite to the very small pressure increase found by 

 A. Wehnklt and J. Frank ^) under special conditions; it has been 

 observed for the first time here in a spectral tube and it offers 

 — especially when the dimensions of the apparatus would be chosen 

 with a view to this purpose — a means to learn something about 

 thé properties (mass) of the gas particles that conduct the current. 

 It has been proved, that we have to do here with a physical effect 

 and we may directly draw the conclusion that the negative ions 

 are no electrons but electric particles with a relatively large mass. 

 From a more detailed investigation we learn that to this phenomenon 

 there corresponds an increase in pressure at the anode. The pressure 

 effect is smaller in gases with lower molecular weight. It is apparently 

 possible to biing these different things into connexion with the diffe- 

 rence in mass, number, velocity of the negative and positive electrons 

 (mass-transport by the electric current). 



B. Hydrogen, neon, helium. 



The observations made on these gases are in so far in agreement 

 with those on nitrogen, that here we may draw the a;eneral con- 

 clusion, that within the limits of j)0ssible observation errors (and within 

 the domain of investigation) the intensity of the spectral lines or 

 bands of all gases investigated is proportional to the supplied energy 

 and that with decrease of pressure the maximum of energy is shifted 

 towards the ultra-violet. Moreover we learn from the observation 



1) Verb. d. .D. phys. Ges. 12, 444, 1910. See also J. Stark, Bolzmann Festschr. 

 399, 1904. 



