The sixth series in the spectrum of atomic hydrogen

Th e fir s t member of the sixth series (6h 2IP -7i 21) in the sp ectrum of at omic hydrogen has been observed at 12.371-', in agreement with the predicted position. Other newly observed lines include the second line of the Pfund series and the third, fOLlr t h, and fif th lines of the Brack e t t series. The source was a water-cool ed discharge tube drawing 640 milliamperes a t 5,000 volts. The t ube was fit ted with a ICBI' le ns, which served also as a windo w for end-on observation . An atomic-hydrogen discharge was maintain ed by admi t tin g water vapo l' through a Hopfi eld leak and pLlmping continuously. A conven tional dispersing and recordin g system ,ras used , con sis tin g of a P erkin-Elmer model 12 spe ctrom eter with a d-c br eaker amplifi er and Spee::!omax recorder. Rela t iv e-inte n s i t ~ mea sureme nts are included.