"That is a piece of Willemite.
"Master Tales of Mystery, Volume 3"
Collected and Arranged by Francis J. Reynolds
Why, only those rays invisible to the human eye, but which make this piece of Willemite glow-the ultra-violet rays."
"Master Tales of Mystery, Volume 3"
Collected and Arranged by Francis J. Reynolds
The samples of the above four substances all showed fluorescence in presence of radium rays, but only the ZnS phosphoresces after exposure to light rays, although the Willemite was phosphorescent after exposure to the ultra-violet.
"The Nature of Animal Light"
E. Newton Harvey