CONTRIBUTIONS TO MOLECULAR PHYSICS 411 



those of the ethereal waves, the latter are absorbed. 

 Briefly defined, then, transparency in liquids, as well 

 as in gases, is synonymous with discord, while opacity 

 is synonymous with accord, between the periods of the 

 waves of ether and those of the molecules on which they 

 impinge. 



According to this view transparent and colorless sub- 

 stances owe their transparency to the dissonance existing 

 between the oscillating periods of their atoms and those 

 of the waves of the whole visible spectrum. From the 

 prevalence of transparency in compound bodies, the gen- 

 eral discord of the vibrating periods of their atoms with 

 the light-giving waves of the spectrum may be inferred; 

 while their synchronism with the ultra-red periods is to be 

 inferred from their opacity to the ultra-red rays. Water 

 illustrates this in a most striking manner. It is highly 

 transparent to the luminous rays, which proves that its 

 atoms do not readily oscillate in the periods which excite 

 vision. It is highly opaque to the ultra-red undulations, 

 which proves the synchronism of its vibrating periods 

 with those of the longer waves. 



If, then, to the radiation from any source water shows 

 itself eminently or perfectly opaque, we may infer that the 

 atoms whence the radiation emanates oscillate in ultra-red 

 periods. Let us apply this test to the radiation from a 

 flame of hydrogen. This flame consists mainly of incan- 

 descent aqueous vapor, the temperature of which, as cal- 

 culated by Bunsen, is 3,259° C, so that, if the penetrative 

 power of radiant heat, as generally supposed, augment 

 with the temperature of its source, we may expect the 

 radiation from this flame to be copiously transmitted by 

 water. While, however, a layer of the bisulphide of car- 



