THEORETICAL. 327 



types of radiation, the one being represented by the 4.75 (i band of CO 

 and COo, the other being represented by the lines of N at 0.90 /a and 

 1.06 [x. The 4.75 fi band of CO and CO, behave in an entirely different 

 manner from all the rest. Its intensity increases with increasing pres- 

 sure (for constant current) of the gas, but never reaches a maximum, 

 becoming asymptotic at 5 to 6 mm. pressure. 



On the other hand, the other bands increase in intensity with in- 

 crease in pressure (for constant current), become a maximum at about 

 2 mm. pressure, and then decrease in intensity with a further increase 

 in pressure, which agrees with observations in the visible spectrum. 



All lines increase in intensity with increase in current, as found 

 in the visible spectrum. 



Condensers in parallel with the vacuum-tube caused a slight increase 

 in the intensity of the lines, due to an increase in the current through 

 the tube. This is due to the well-known fact that on account of the 

 high self-induction of the coil, the discharge of the condenser takes the 

 easier path through the vacuum-tube. The whole shows that the bands 

 of N (He), and H, near the visible spectrum, are related to the visible 

 bands, while the 4.75 /x band is of an entirely different type. 



Returning to the theory, it is interesting to recall Angstrom's (loc. 

 cit.) predictions in regard to the mechanism which produces these 

 radiations. As noticed elsewhere, he found that the total radiation 

 increases, while the luminous radiation decreases with the increase in 

 pressure of the gas, and concluded that there is a "regular" and an 

 "irregular" radiation present during the electrical discharge. This 

 would tend to change the efficiency of a vacuum-tube, as found by 

 Angstrom and by Drew. 



In the present work, the decrease in infra-red radiation (4-75 /* 

 band) and the simultaneous increase in the visible radiation, with 

 decrease in pressure, explains very clearly the rise in efficiency of 

 vacuum-tubes. It also explains why the total radiation passes through 

 a minimum as observed by Angstrom, and by Drew (loc. cit.). 



In connection with the theoretical work just mentioned the behavior 

 of these two types of radiation may be explained in the following man- 

 ner. Consider the lines in and near the visible spectrum. At high 

 pressures the electrons will not attain a high speed on account of the 

 numerous neutral molecules, and their freedom of motion will be 

 limited. At a lower pressure their freedom of motion will be greater, 

 the number of collisions will be more frequent, the ionization will in- 

 crease, and the electrical temperature,' which is proportional to the mean 

 square of the ionic speeds, will attain a maximum. At a still lower 



