Edward Charles Pickering
The Pickering series (also known as the Pickering–Fowler series) consists of three lines of singly ionized helium found, usually in absorption, in the spectra of hot stars like Wolf–Rayet stars. The name comes from Edward Charles Pickering and Alfred Fowler. The lines are produced by transitions from a higher energy level of an electron to a level with principal quantum number "n" = 4. The lines have wavelengths: