POLARIZED SPECTRA OF DOUBLE CHLORIDES. 121 



(6) Variations in the average interval for the four salts are scarcely 

 greater than the errors of observation, but there are indications of a 

 very slight decrease of interval with increase of molecular weight, and 

 this applies alike to fluorescence and absorption series. 



(7) The position, in the spectrum, of a given band varies slightly but 

 systematically with the molecular weight of the salt. The order of 

 diminishing wave-lengths is K, NH 4 , Rb, Cs; the shift from K to Cs 

 being of the order of 5 A. u. This shift is in the same direction from 

 red toward violet for all the homologous series and of the same size 

 within the errors of observation. 



(8) Cooling to the temperature of liquid air produces the usual 

 narrowing of bands, apparent shifts of position, and apparent changes 

 of interval, all of which changes are explained by the relative enhance- 

 ment or diminution of components of the bands. 



