158 Profs. Liveing and Dewar. Spectra of the [Feb. 5, 



Spectrum of the Arc in Nitric Oxide. 



In this gas a very long arc could be obtained. The violet and 

 ultra- violet bands were well seen, the seven bine bands were seen but 

 weaker. The bine and green hydrocarbon bands were also seen well 

 when the arc was short, not so well when the arc was long. The 

 length of the arc did not seem to affect the brightness of the violet 

 bands. Many metallic lines of iron, calcinm, and magnesium were 

 seen. 



Spectrum of the Arc in Ammonia. 



In ammonia only a short arc could be obtained. All the bands were 

 faint, but the seven blue, the violet and ultra-violet bands were 

 always visible. 



These experiments with different gases eliminate to a large extent 

 the influence of electric conductivity on the character of the spectrum ; 

 but we intend to examine more thoroughly the effect of this variable 

 by observation of the arc in some of these gases under different condi- 

 tions of pressure. 



Spectra of Flames of Carton Compounds. 



Besides the experiments with the arc above described, we have made 

 some observations of the spectra of names of sundry compounds of 

 carbon. 



In the flame of cyanogen, prepared from well dried mercury 

 cyanide, passed over phosphoric anhydride inserted in the same tube, 

 and burnt from a platinum jet fused into the end of the tube, we found, 

 as Plucker and Hittorf had found, that the hydrocarbon bands were 

 almost entirely absent, only the brightest green band was seen, and 

 that faintly. The seven blue and the violet bands on the other hand 

 were, as described by other observers, well developed, the three indigo 

 bands less brightly. A series of bands at the red end, also described 

 by Dibbits and by Plucker and Hittorf, was also visible. These 

 bands are sharply defined on the more refrangible side and fade away 

 on the other side, and extend beyond the orange hydrocarbon bands on 

 the red side. They have not been seen by us in the spectra of the arc, 

 but they may very well have been present in some of those spectra and 

 yet not seen because of the continuous spectrum of the arc, which, not 

 being very much dispersed at the red end, was bright enough to 

 overpower any such bands. This continuous spectrum seems much 

 stronger when well purified carbon electrodes are used than when they 

 contain metallic impurities to the extent commonly present in them. 

 We may remark that in general we see only six bands, or rather six 

 maxima of light, in the violet series, as stated by Dibbits, not seven, as 

 stated by Morren and by Plucker and Hittorf ; and in the ultra-violet 

 we always see five maxima of light, instead of four as given by 



