"How long does it retain its light, father?"

"That is uncertain. For some hours in a darkened room, the light gradually growing fainter, but if a bright day follows, the figures stand out on the following night as brightly as before; while if the day is dull they show up but faintly at night. I see not that any use can come of such a thing, for the light is at all times too faint to be used for reading unless the page is held quite close to it. Come downstairs with me and I will show you the head of one of the old Roman statues that was dug up near Rochester, and which I bought for a few pence last year."

They went down into the laboratory. The light was burning. "There you see, Edgar, I have painted this head with the stuff, and now you can see nothing more unusual than if it had been daubed with whitewash. Now I will extinguish the lamp."

Prepared as he was, Edgar nevertheless stepped back with an exclamation of surprise and almost awe. The head stood out in the darkness with startling distinctness. It had the effect of being bathed in moonlight, although much more brilliant than even the light of the full moon. It seemed to him, indeed, almost as if a faint wavering light played around it, giving the stern face of the old Roman a sardonic and evil expression.