Yet here was the one great question, Whence had come the impulse that had sent the famous Z99 to her fate?

“Could it have been through something internal?’ I asked.  “Could a current from one of the batteries have influenced the receiving apparatus?”

“No,” replied the captain mechanically.  “I have a secret method of protecting my receiving instruments from such impulses within the hull.”

Kennedy was sitting silently in the corner, oblivious to us up to this point.

“But not to impulses from outside the hull,” he broke in.

Unobserved, he had been bending over one of the little instruments which had kept us up all night and bad cost a tedious trip to New York and back.

“What’s that?” I asked.

“This?  This is a little instrument known as the audion, a wireless electric-wave detector.”

“Outside the hull?” repeated Shirley, still dazed.

“Yes,” cried Kennedy excitedly.  “I got my first clue from that flickering Welsbach mantle last night.  Of course it flickered from the wireless we were using, but it kept on.  You know in the gas-mantle there is matter in a most mobile and tenuous state, very sensitive to heat and sound vibrations.

“Now, the audion, as you see, consists of two platinum wings, parallel to the plane of a bowed filament of an incandescent light in a vacuum.  It was invented by Dr. Lee DeForest to detect wireless.  When the light is turned on and the little tantalum filament glows, it is ready for business.

“It can be used for all systems of wireless—­singing spark, quenched spark, arc sets, telephone sets; in fact, it will detect a wireless wave from whatever source it is sent.  It is so susceptible that a man with one attached to an ordinary steel-rod umbrella on a rainy night can pick up wireless messages that are being transmitted within some hundreds of miles radius.”

The audion buzzed.

“There—­see?  Our wireless is not working.  But with the audion you can see that some wireless is, and a fairly near and powerful source it is, too.”

Kennedy was absorbed in watching the audion.

Suddenly he turned and faced us.  He had evidently reached a conclusion.  “Captain,” he cried, “can you send a wireless message?  Yes?  Well, this is to Burke.  He is over there back of the hotel on the hill with some of his men.  He has one there who understands wireless, and to whom I have given another audion.  Quick, before this other wireless cuts in on us again.  I want others to get the message as well as Burke.  Send this:  ’Have your men watch the railroad station and every road to it.  Surround the Stamford cottage.  There is some wireless interference from that direction.’”