Diagram, arc spectra of thallium, indium and gallium by Henry Wilde Line spectrum of thallium compared with the spectra of indium and gallium. Subject: Spectroscopy / Chemistry A print of this diagram was published in volume 53 of the Proceedings of the Royal Society alongside the paper 'On the spectrum of thallium, and its relation to the homologous spectra of indium and gallium'. 1893