the light of the staircase lamp.

"Apologise to our friends," it ran, "for the slight change of programme.
Norbury is anxious that I should get my experiments over before the
Director returns, so as to save discussion. He has asked me to begin
to-night and says he will see Mr. and Miss Bellingham here, at the
Museum. Please bring them along at once. The hall porters are instructed
to admit you and bring you to us. I think some matters of importance may
transpire at the interview.--J.E.T."

* * * * *

"I hope you don't mind," I said apologetically, when I had read the note
to Ruth.

"Of course I don't," she replied. "I am rather pleased. We have so many
associations with the dear old Museum, haven't we?" She looked at me for
a moment with a strange and touching wistfulness and then turned to
descend the stone stairs.

At the Temple gate, I hailed a hansom and we were soon speeding westward
and north to the soft tinkle of the horse's bell.

"What are these experiments that Doctor Thorndyke refers to?" she asked
presently.

"I can only answer you rather vaguely," I replied. "Their object, I
believe, is to ascertain whether the penetrability of organic substances
by the X-rays becomes altered by age; whether, for instance, an ancient
block of wood is more or less transparent to the rays than a new block
of the same size."

"And of what use would the knowledge be, if it were obtained?"

"I can't say. Experiments are made to obtain knowledge without regard
to its utility. The use appears when the knowledge has been acquired.
But in this case, if it should be possible to determine the age of any
organic substance by its reaction to X-rays, the discovery might be of
some value in legal practice--as in demonstrating a new seal on an old
document, for instance. But I don't know whether Thorndyke has anything
definite in view; I only know that the preparations have been on a most
portentous scale."

"How do you mean?"

"In regard to size. When I went into the workshop yesterday morning, I
found Polton erecting a kind of portable gallows about nine feet high,
and he had just finished varnishing a pair of enormous wooden trays,
each over six feet long. It looked as if he and Thorndyke were
contemplating a few private executions with subsequent post-mortems on
the victims."

"What a horrible suggestion!"

"So Polton said, with his quaint, crinkly smile. But he was mighty close
about th