244 THE POPULAR SCIENCE MONTHLY 



1. Neutral " aggregates " of charged particles possessing, in general, 

 translatory and rotatory energy. When undisturbed from without 

 these aggregates would have little if any external electric field. When 

 the equilibrium of such a system is disturbed by collisions or by electro- 

 magnetic waves, it may possess temporary fields that will serve as the 

 source of heat and light radiation. This radiation may be due to a 

 rapid oscillatory motion that may be radial, transverse or tangential 

 and would probably be characterized by a definite period. On account 

 of the magnitude of the forces necessary for stable equilibrium, the 

 period of the radiation would probably be small. The spectroscopic 

 models of Thomson, Nagaoka and others are of this type. 



2. " Aggregates " may possess charged parts ; these may be so far 

 apart from each other that local fields of considerable intensity may exist. 

 If such an aggregate were to rotate, an alternating electric field would 

 result and radiations would be emitted. This radiation, depending on 

 a central acceleration, would vary in period with each impact, so that 

 the various periods emitted would vary about a mean, which would 

 depend on the average rotational energy before impact and the nature 

 of the impact. 



3. Freely charged particles torn from neutral " aggregates " will 

 radiate energy when their velocity is changed. The quantity of this 

 radiation will vary with the velocity and the acceleration. The break- 

 ing up of the neutral " aggregates " may be called ionization if the 

 resulting parts are charged. Ionization processes may take place within 

 molecules and this is believed to be the condition existing in many 

 kinds of organic compounds when they absorb light or heat. 



The relation between ionization and luminosity is not yet clear. 

 Some physicists believe that the two are related to each other and that 

 luminosity becomes perceptible when the intensity of ionization is suffi- 

 •ciently great. It has been stated that a gas may become luminous 

 ■when one molecule in every (10)'^ is ionized. This would mean that the 

 (expenditure of about (10)"^ ergs is necessary to excite luminosity. 



loisrizATioisr and Light Emission axd Absorption 



There appears to be considerable evidence supporting the view that 

 some band spectra such as those of bromine and iodine may be due to 

 the dissociation of molecular S3^stems or to a recombination of the disso- 

 ciated parts. Ladenburg has found that luminous hydrogen gives an 

 anomalous dispersion in the neighborhood of H<,, while this kind of dis- 

 persion is absent in ordinary hydrogen. The phenomena of dispersion 

 indicate that different series of lines in a spectinim may be emitted by 

 very different kinds of vibrating centers, while a particular center may 

 emit only a single line of a series, depending on the manner of its 

 excitation. Faintness in the intensity of lines may be due to the fact 

 that there are very few light centers emitting the given line, or that the 



