108 Mr. Piazzi Smyth on Carbon and Carbo- Hydrogen, 



The startling- deduction that the spectrum belongs to carbon 

 is claimed to Lave been proved by Dr. Attfield, Dr. Marshall 

 Watts, and other most able men, from their having found one 

 and the same spectrum in all compounds of carbon — i. e. not 

 only in carbo-hydrogens, but in carbo-oxygens and carbo- 

 nitrogens of several kinds, first in blowpipe flames, and then 

 in gases illumined by the electric spark, both at ordinary at- 

 mospheric pressure and in vacuum-tubes. 



Of these several methods I have only been able to test the 

 last through many varieties of carbon, and other, compounds. 

 But that method I have not only had superior vision of by 

 means of my recently constructed end-on tubes (made for me 

 by M. Salleron, 24 Rue Pavee au Marais, Paris), but have 

 examined its manifestations under more powerful dispersion 

 than most of my predecessors. And with what result ? With 

 the astonishment of finding that after all, while something 

 certainly visible is undoubtedly common to all the tubes, there 

 is another thing visible, in some of them even to greater 

 brightness, and is so seen in carbo-hydrogen tubes only. 



First, let us be quite clear on what that previous something 

 was, which was common to all the tubes. 



It is a spectrum somewhat like the coal-gas and air blow- 

 pipe-flame spectrum, having, besides other features, five co- 

 loured bands — red, citron, green, blue, and violet — mid each 

 band capable of breaking up into thin compound lines under 

 high dispersion. But no band of one of these spectra begins 

 exactly in the same place as any band in the other ; nor are 

 its minuter constructional lines in the least degree similar. 

 Dr. Watts, moreover, does recognize this vacuum-tube spec- 

 trum as being different from the coal-gas blowpipe-flame's 

 spectrum, and calls it therefore " the second spectrum of car- 

 bon." A carbon-spectrum, too, I will not deny it may be; for 

 the temperature of the disruptive induction-spark under which 

 it is produced, may be quite enough to dissociate even that 

 element from its compounds and keep its vapour incandescent. 

 But let us examine the said possible carbon-spectrum from 

 tube to tube, and note the variations. 



Now here our first entry must be, that this alleged tube 

 carbon-spectrum appears in every vacuum-tube I possess, whe- 

 ther purporting to contain a compound of carbon or not ; but 

 it varies in brightness. Hence it appears moderately only in 

 tubes of 



Air, Ozone, 



Nitrogen, Hydrogen, and 



Oxygen, Nitrous Oxide ; 



