At first it was hypothesized that the line might be due to an unknown element, which was named nebulium—a similar idea had led to the discovery of helium through analysis of the Sun's spectrum in 1868.
Nejprve si vytvořil hypotézu, že na této délce vyzařuje dosud neznámý prvek, který nazval nebulium — podobná úvaha vedla k objevu hélia ve slunečním spektru v roce 1868.