EFFECT OF PRESSURE UPON ARC SPECTRA.-(JOLL). 



atmosphere. Except for a very few readings which are marked with a ruinitx sign, 

 the displacements are towards the side of greater wave-length. The measurements 

 in brackets were not considered sufficiently reliable to include in the displacement 

 diagram. 



TABLE IV. Displacements in Thousandths of an Angstrom Unit. 



(3) Displacement Diagram. The relation between the displacement of the gold 

 lines and the pressure of the surrounding gas is shown graphically in Diagram 1, in 

 which the abscissfe represent excess of pressure above I atmosphere and the ordinates 

 the displacements measured in thousandths of an Angstrom unit. 



Each line on the diagram represents the behaviour of the particular spectral line 

 indicated by the letter attached to it. 



The readings were made at those pressures which have been indicated on the base 



line. 



(4) The Relation between the Displacement and Wave-length. 'the investigation 

 of the copper arc under pressure indicated that for the non-series lines (those not 

 falling into the series described by KAYSER and RUNGE) there exists a relation 

 between the displacements and the wave-lengths of the spectral lines, the former 

 being proportional to some power of the latter, which in those experiments was " at 

 least as great as the third power and possibly as high as the sixth." 1 



* DUFFIELD, 'Phil. Trans.,' A, vol. 209, p. 205, 1908. 



