1904.] On Flame Spectra. 85 



found in the flame spectrum are those which are the strongest lines in 

 the arc spectrum. In certain cases, some of the more intense arc lines 

 are absent, whereas less intense arc lines are to be found in the flame 

 spectrum. On the other hand, none of the characteristic lines of the 

 spark spectrum are ever seen in the flame spectrum. The resemblance, 

 however, is very marked between the flame spectrum and that of the 

 spark which has been made oscillatory by the introduction of a self- 

 induction into the discharging circuit of a condenser. In the latter 

 case, as is well known from the work of Dr. Hemsalech, the spark 

 spectrum is 'considerably simplified.* Moreover, although the flame 

 spectrum will contain only the lines which belong to the spectrum of 

 the oscillatory spark, yet all the lines of the latter will not be found in 

 the flame spectrum, the missing lines being those which are peculiar to 

 the ordinary spark spectrum, and which only exist in the immediate 

 neighbourhood of the electrodes, becoming shorter and shorter, and 

 finally disappearing as the self-induction is increased. 



The preceding paragraph refers to metals other than those belonging 

 to the iron group. On the contrary, there is a most striking similarity 

 between the flame spectra of iron, of nickel, and of cobalt, and the 

 oscillatory spark spectra of the same metals in the region included 

 between about 4300 and 2700 Angstrom units. The similarity of 

 the two spectra is so great that, except for very small differences of 

 intensity, the oscillatory spark spectrum, which is photographed as a 

 comparison spectrum in the centre of the flame spectrum, appears to be 

 a prolongation of the latter. It should be noticed that if in the visible 

 portion of the spectrum certain lines appear to be missing, it is 

 doubtless because the continuous spectrum prevents these feeble lines 

 from being seen. This explains why M. Gouy was not able to observe 

 the nickel lines which are found on the photographs taken with various 

 salts of nickel, viz., the sulphate, chloride, and ammoniacal chloride. 

 In the ultra-violet the spectrum of the flame appears to fade away a 

 little more rapidly than that of the oscillatory spark, but it is probable 

 that this difference would be reduced by prolonging the time of 

 exposure ; since it is, of course, the radiations of the shortest wave- 

 length which are most absorbed by different media. 



It is very probable that the reason for this similarity between the 

 spectrum of the flame and the spectrum of the oscillatory spark is 

 entirely a question of temperature. On the one hand, the increase in 

 the number of lines of the flame spectrum obtained by the use of the 

 sprayer may be attributed to the fact that the hottest regions of the 

 flame take part in the production of the phenomena, and, on the other 

 hand, the diminution in the number of lines in the spark spectrum 

 when the spark becomes oscillatory is due to a diminution of its 

 temperature. 



* ' Sur les Spectres d'Etincelles.' Paris, Hermann. 



