MODELS OF POSITIVE ION 319 



the radiation therefrom necessarily exist only 

 during the period of radiation.^ 



It is generally admitted, although disputed by 

 some eminent authorities, that a gas cannot be 

 rendered luminous by the mere process of heat- 

 ing until chemical action, in some form or another, 

 takes place ; for instance, the presence of a salt 

 in such cases, in which it may act chemically, is 

 indispensable to the production of a spectrum. 

 The free periods would, therefore, depend upon the 

 presence of a foreign substance. The same atom 

 will always give out the same spectrum, but the 

 free periods will exist only when the corpuscle 

 and the atom are within each other's reach. Thus 

 the actual number of degrees of freedom in an 

 atom will depend upon the arrangement of cor- 

 puscles around it, so that the Boltzmann-Maxwell 

 law is not interfered with as long as the gas is 

 not radiating, the number of degrees of freedom 

 in an atom, as indicated by its spectrum, in no 

 way corresponding with its number of degrees of 

 freedom when not radiating. The actual number 

 of internal degrees of freedom in an atom will 

 depend upon the number of corpuscles that it 

 carries, and these need not be more than one or 

 two or three as indicated by the ratio of the 

 specific heats. 



The great complex of lines in the spectrum of 

 an element will depend upon the closeness of the 



1 This appears to be a most important point in the kinetic 

 theory. 



