“Ultraviolet rays have recently been found very valuable in the examination of questioned documents.  By the use of a lens made of quartz covered with a thin film of metallic silver, there has been developed a practical means of making photographs by the invisible rays of light above the spectrum—­these ultraviolet rays.  The quartz lens is necessary, because these rays will not pass through ordinary glass, while the silver film acts as a screen to cut off the ordinary light rays and those below the spectrum.  By this means, most white objects are photographed black and even transparent objects like glass are black.

“I obtained the copy of this will, but under the condition from the surrogate that absolutely nothing must be done to it to change a fibre of the paper or a line of a letter.  It was a difficult condition.  While there are chemicals which are frequently resorted to for testing the authenticity of disputed documents such as wills and deeds, their use frequently injures or destroys the paper under test.  So far as I could determine, the document also defied the microscope.

“But ultraviolet photography does not affect the document tested in any way, and it has lately been used practically in detecting forgeries.  I have photographed the last page of the will with its signatures, and here it is.  What the eye itself can not see, the invisible light reveals.”

He was holding the document and the copy, just an instant, as if considering how to announce with best effect what he had discovered.

“In order to unravel this mystery,” he resumed, looking up and facing the Elmores, Kilgore, and Hollins squarely, “I decided to find out whether any one had had access to that closet where the will was hidden.  It was long ago, and there seemed to be little that I could do.  I knew it was useless to look for fingerprints.

“So I used what we detectives now call the law of suggestion.  I questioned closely one who was in touch with all those who might have had such access.  I hinted broadly at seeking fingerprints which might lead to the identity of one who had entered the house unknown to the Godwins, and placed a document where private detectives would subsequently find it under suspicious circumstances.

“Naturally, it would seem to one who was guilty of such an act, or knew of it, that there might, after all, be finger-prints.  I tried it.  I found out through this little tube, the detectascope, that one really entered the room after that, and tried to wipe off any supposed finger-prints that might still remain.  That settled it.  The second will was a forgery, and the person who entered that room so stealthily this afternoon knows that it is a forgery.”

As Kennedy slapped down on the table the film from his camera, which had been concealed, Mrs. Godwin turned her now large and unnaturally bright eyes and met those of the other woman in the room.

“Oh—­oh—­heaven help us—­me, I mean!” cried Miriam, unable to bear the strain of the turn of events longer.  “I knew there would be retribution—­I knew—­I knew—­”