Spectrum of Trebly Ionised Lead

THE spectrum of trebly ionised lead, which has been studied by several authors ending with S. Smith¹, requires modification in several respects. I have shown that 7p²P-7d²D is really 7p²P-8s²S and confirmed this by obtaining further combinations with the 8s²S term. This provides a series of ²S terms the values of which can be accurately calculated by Hicks's formula. 6s²S comes out equal to 340180, giving an ionisation potential of 41.9 volts.