practically wipe out your troubles in sending and receiving?"

"Because there is even less of it in the world than there is of
radium," was the startling reply. "At present Z. 2. X. costs far more
than radium. It is the most intensely radio-active stuff in the world.
It is capable of being wrought into metal if anybody had ever found
enough of it, but except for a small deposit in South Africa, which
has been devoted to experimental purposes, nobody has any.

"But enough of that now. That is only a dream. I am anxious, though,
to test out my present apparatus thoroughly, and to do it I shall need
the help of you boys."

"In what way?" asked Jack.

"In giving it a thorough trial to ascertain over how great a space I
can transmit wireless speech."

"Are you going to put up another station outside the grounds?" asked
Tom.

"No; I don't want to attract attention to my experiments. You boys
have a wireless telegraph outfit on your Wondership?"

Jack nodded. He was curious, as was Tom, to know the Professor's plan.
They did not have long to wait.

"I wish you would get the machine ready to install a radio-telephone
outfit in its place. In that way I can gauge the limits of my
invention without attracting undue attention, as everybody in this