BY COLOURED MEDIA. 485 



their subdivision according to the condition above ex- 

 plained ; and suppose, further, that the other ends (E) 

 of all the reunited pipes opened out, in like manner, into 

 another chamber, at some considerable distance from the 

 first, and separated from it by masonry or some material, 

 filling in all the intervals between the pipes, so as to be 

 completely impervious to sound. Things being so dis- 

 posed, let the whole scale be sounded, or a concert of 

 music performed in the first chamber, then will every 

 note, except that one to which the pipes are thus ren- 

 dered impervious, be transmitted. The scale, therefore, 

 so transmitted, will be deficient by that note, which has 

 been, to use the language of photologists, absorbed in its 

 passage. If several such chambers were disposed in 

 succession, communicating by compound pipes, ren- 

 dered impervious (or ///ztuned, as we may term it) to so 

 many different notes, all these would be wanting in the 

 scale on its arrival in the last chamber ; thus imitating a 

 spectrum in which several rays have been absorbed in 

 their passage through a coloured medium. 



(i i.) In my Article on Light, above referred to, Art. 505, 

 I have suggested, as a possible origin of the fixed lines 

 in the solar spectrum, and (pan ratione) of the deficient 

 or less bright spaces in the spectra of various flames, that 

 the same indisposition in the molecules of an absorb- 

 ent body to permit the passage of a particular coloured 

 ray through them, may constitute an obstacle, in limine, to 

 the production of that ray from them. The following easy 

 experiment will explain my meaning. Take two tuning 

 forks of the same pitch, and heating the ends of them, 



