“Not all,” broke in Kennedy remorselessly.  “Yes, madame, send for Dr. Scott.  Why is he not here?”

Prescott, with one hand on my arm and the other on Dr. Burnham’s, was moving toward the door.

“One moment, Prescott,” interrupted Kennedy, detaining him with a look.  “There was something I was about to say when Dr. Burnham’s urgent message prevented it.  I did not take the trouble even to find out how you obtained that little globule of molten gold from the crucible of alleged copper.  There are so many tricks by which the gold could have been ‘salted’ and brought forth at the right moment that it was hardly worth while.  Besides, I had satisfied myself that my first suspicions were correct.  See that?”

He held out the little piece of mineral I had already seen in his hand in the alchemist’s laboratory.

“That is a piece of willemite.  It has the property of glowing or fluorescing under a certain kind of rays which are themselves invisible to the human eye.  Prescott, your story of the transmutation of elements is very clever, but not more clever than your real story.  Let us piece it together.  I had already heard from Dr. Burnham how Mr. Haswell was induced by his desire for gain to visit you and how you had most mysteriously predicted his blindness.  Now, there is no such thing as telepathy, at least in this case.  How then was I to explain it?  What could cause such a catastrophe naturally?  Why, only those rays invisible to the human eye, but which make this piece of willemite glow—­the ultra-violet rays.”

Kennedy was speaking rapidly and was careful not to pause long enough to give Prescott an opportunity to interrupt him.

“These ultra-violet rays,” he continued, “are always present in an electric arc light though not to a great degree unless the carbons have metal cores.  They extend for two octaves above the violet of the spectrum and are too short to affect the eye as light, although they affect photographic plates.  They are the friend of man when he uses them in moderation as Finsen did in the famous blue light treatment.  But they tolerate no familiarity.  To let them—­particularly the shorter of the rays—­enter the eye is to invite trouble.  There is no warning sense of discomfort, but from six to eighteen hours after exposure to them the victim experiences violent pains in the eyes and headache.  Sight may be seriously impaired, and it may take years to recover.  Often prolonged exposure results in blindness, though a moderate exposure acts like a tonic.  The rays may be compared in this double effect to drugs, such as strychnine.  Too much of them may be destructive even to life itself.”

Prescott had now paused and was regarding Kennedy contemptuously.  Kennedy paid no attention, but continued:  “Perhaps these mysterious rays may shed some light on our minds, however.  Now, for one thing, ultra-violet light passes readily through quartz, but is cut off by ordinary glass, especially if it is coated with chromium.  Old Mr. Haswell did not wear glasses.  Therefore he was subject to the rays—­the more so as he is a blond, and I think it has been demonstrated by investigators that blonds are more affected by them than are brunettes.