Band and Line Spectra of the same Metalhe Elements. 121 
to no other conclusion than that the composite bands are the result of vibrations 
taking place within the molecule, and not to the vapour-pressure ; neither to the 
great volume of vapour, nor to the vapour-density of the molecule. 
As the composite bands in the spectrum of silver are analogous to those of 
copper, and whereas it has been shown that silver cannot be submitted to the same 
crucial quantitative experiments, it may be very reasonably assumed that the 
similarly constituted bands in the spectrum of silver have a similar origin. ‘This 
is the most probable explanation, because there are other bands in the spectrum of 
silver which have been shown by their behaviour to have a different origin, and 
one depending apparently upon the great density of the silver vapour. 
{ Sirver—Deseription of Spectrum. 
