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.
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