Examining the spectrum of the arc of manganese, he determined that the optical spectra of complex atoms consisted of groups of lines –which he called "multipletes"- between which existed certain characteristic regularities.
Examinando o espectro do arco de manganeso, determinou que o espectro óptico de átomos complexos consistía en grupos de liñas, que chamou "multipletes", entre as que existían regularidades características.