﻿414 M. A. Wullner on the Spectra of 



multaneous interposition of a Ley den jar in the circuit of the 

 induction-current. A brilliant bright-green light is then ob- 

 tained in the tube, and the six groups of lines become truly- 

 splendid. At the same time the parts lying between the groups 

 of lines become brighter, yet not to such an extent as to change 

 the character of the spectrum. The tube then afterwards ex- 

 hibits the same spectrum even without a Leyden jar. 



This spectrum is also obtained with the extremest degree of 

 rarefaction if the spark of Holtz's machine with a condenser be 

 caused to pass, or if a small Leyden jar with a short striking-dis- 

 tance be discharged through it. Care must at the same time be 

 taken not to have the striking-distance too great ; otherwise the 

 calcium-spectrum, or the continuous spectrum of ignited glass 

 with the dark line D, occurs. 



With a tube once arranged I have frequently observed this 

 spectrum for fourteen days together and compared it with others ; 

 so accurately closed were Dr. Geissler's glass stopcocks. 



6. The phenomenon of a hydrogen-tube at its extreme ex- 

 haustion furnishing a third spectrum essentially different from the 

 earlier ones observed is so surprising, that the question must be 

 considered whether this spectrum belongs in fact to pure hydro- 

 gen, or is not due to other elements standing in connexion with 

 the tube. It might be believed that it was a spectrum of alumi- 

 nium, of which the electrodes consisted, or of mercury, of which, 

 perhaps, vapours had distilled over into the tubes, or of phos- 

 phorus or sulphur, as the gas was dried with phosphoric and sul- 

 phuric acids, or, finally, that some of the fat with which the 

 stopcocks were slightly coated had evaporated and had entered 

 the tubes, and thus that the lines belonged to the spectrum of 

 carbon. 



As regards carbon, the description which Pliicker gives of the 

 spectra of this element"* shows that none of the groups of lines 

 of the kind described occur in them ; and in an investigation of 

 the spectrum in a tube filled with carbonic acid, we found it of 

 the same character as Pliicker describes. 



In reference to the sulphuric-acid spectrum, Pliicker f states 

 that it is one of the most beautiful spectra and at the same time 

 most rich in colour, it consists of bright luminous bands on a 

 black ground; and he then counts three red, one orange, one yel- 

 low, four green, nine blue and violet bands. He mentions at the 

 same time that, using anhydrous sulphuric acid, this spectrum 

 can only be obtained with the large induction coil. All this 

 proves that the spectrum described cannot be due to sulphuric 



* Philosophical Transactions for 1865. 

 t Pogg. Ann. vol. cxiii. 



