246 Scientific Proceedings, Royal Dublin Society. 
conditions with respect to spark and pressure ; but when the pressure 
is reduced to less than one millimetre, it is found that all the 
nitrogen bands have disappeared, and also the narrow bands, 
leaving just the two most refrangible of the lines XA 38380 and 
3837 approximately, which are a pair, with a similar pair AA 5209 
and 5200. From these changes, it appears more than probable that 
they are the spectrum of magnesium nitride, which is decomposed 
gradually until nothing but the two pairs of lines remain to 
represent the magnesium in the compound. 
