diamond was perfect. Elsa Hoffman was gazing at
her, too, in tense interest. De Guerre was outwardly cool, Margot
openly cynical, Preston leaning forward in ill-suppressed excitement.

For a moment Kennedy paused again, as if allowing all to collect
themselves before he took them by assault.

"I have lately been studying," he remarked casually, "the experiments of
Dr. Von Pfungen of Vienna showing the protective resistance of the human
skin against an electric current. Normally, this resistance averages
from seventy to eighty thousand ohms. In the morning, owing to the
accumulation of waste products, the resistance may mount to almost
double. In persons suffering from nervous anxiety, it decreases to five
thousand and even down to a thousand ohms in cases of hysteria. Von
Pfungen has also measured a human being's emotional feelings by the
electric current. I have a copy of his instrument here. There is one
person who sits gripping the carbon electric handle connected with this
galvanometer who, to begin with, had a resistance of over sixty
thousand. But when I began to tell of how Rawaruska met her death, of
the hypothetical case I have built up by my observations and experiments
here in this very laboratory, the needle of the galvanometer started to
oscillate downward. It went down until it reached thirty-eight thousand
at the mention of murder. When I said the case was perfect, it had got
as low as under twenty thousand, swinging lower and lower as the person
saw hope depart!"

Kennedy was no longer paying any attention to the little instrument. As
I followed him, I became more and more impatient. What was it he had
discovered? Who was it?

"Preston," cried Kennedy, suddenly wheeling on the young doctor,
"through your regard--honorable, I am sure--for Rawaruska you have let
yourself be drawn into doing a little amateur detective work. Let me
warn you. Instead of clearing up the case, you merely laid yourself open
to suspicion. Fortunately the galvanometer absolves you. You should have
known that Cecilie was only a tool. De Guerre, your black wallet, that
all diamond dealers carry--thank you, Wade--that's it."

Kennedy had turned from Preston to Cecilie, then to De Guerre so
suddenly that no one was prepared for the signal he gave to the customs
officer.

Wade had covered the surprised dealer and was now emptying out the
contents of the wallet.

There, on the table, gleaming in the light of the laboratory, lay